Solar PV is now the most cost efective energy source.

[electrodacus]

While hard to believe Solar is the most cost effective energy source at least for individual use not sure about large scale production.
I live in a cold but relatively sunny climate and after evaluating all energy sources for my offgrid house I decided that I will be using solar PV energy to heat my house.
Currently I use propane that is an order of magnitude more expensive about 25 cent/kWh vs just 2.4cent/kWh for PV panels.
Most people in the world use a mix of grid electricity and natural gas for house energy needs where natural gas is significantly less expensive than electricity (at least 4 to 5x) per unit of energy so house heating and hot water that is usually more than half of a typical house energy needs is delivered by natural gas.
Heating with solar PV panels can be extremely simple. Just connect a long wire with appropriate resistance to the PV panel output and you just made a completely solid state heater. You can drop that cable in water and you made a water heater. Problem with this simple approach is that is not very efficient best case 80% efficient in a clear sunny day with perfectly calculated resistive element and can be lower than 20% efficient in a completely overcast day.
That is why I came up with a simple but effective solution called Digital MPPT thermal controller (no expensive and unreliable DC-DC converters involved).

If you are curios on how Digital MPPT thermal controller works you can read my presentation about that here http://electrodacus.com/DMPPT450/dmppt-presentation-v01.pdf it is Open Source so there are no secrets all is explained and I think is educational even if you are not interested in the Digital MPPT thermal controller.




Yes the DMPPT450 will be on Kickstarter together with new version of SBMS but what I'm most interested in is your opinion about the Solar PV heating (cooling also possible using peltier elements but I need no cooling at my location in Canada and even where cooling is needed it represents a much smaller percentage of the total house energy use so is less important).   

  Below there is a long discussion regarding heat pumps and their COP (Coefficient of performance) when cascaded (two stage) please ignore all since I was wrong about the COP o such a system and if you want the correct answer you can see first post in page 3.

[TechnicalBen]

Are you considering lifespan costs?
I've only done back of the napkin stuff myself for "pie in the sky" imaginary projects. But I was getting the same cost as a small gas/petrol/diesel heater but a more elegant solution to burning stuff. Batteries were the biggest possible cost, so other forms of storage (heat sinks underground etc) could work out better. But I did read up that Solar uses more carbon in production than it saves in use... and can at times miss energy or economic returns too.

But it is entirely dependent on the sale and install price, along with the expected lifespan. And the stuff I've read relates to industrial/national production not small scale home use...

[djacobow]

At the utility scale, in places with good solar resource, PV can indeed be cheaper than prevailing sources (gas combined cycle, coal) on a /kWh basis. PV advocates call this "grid parity" -- and it is a real thing. PV is usually not cheaper than wind in windy places, but many places are not suitable for that.

However, you cannot run a power system from PV alone (the sun is intermittent, not dispatchable, and doesn't shine at night), so the /kWh basis is not quite the right way to think about.

Furthermore, there is an interesting phenomenon in places with lots of PV penetration, where the existence of the PV actually makes the output from the gas plant _appear_ more expensive on a /kWh basis. It happens when the owners of a gas- or coal-powered resource needs to recoup the cost of the plant over smaller and smaller kWh sales, because that utility is getting more energy from PV and wind. What's interesting in this case is that the gas or coal plant is still needed (because of flexibility) but much less energy is needed from it.


As for residential solar for heating, why not just heat your storage medium / working fluid directly? Why go through the electrical step? It will make substantially more efficient use of the sunlight. The technology for this has existed for a very long time.

[electrodacus]

Are you considering lifespan costs?
I've only done back of the napkin stuff myself for "pie in the sky" imaginary projects. But I was getting the same cost as a small gas/petrol/diesel heater but a more elegant solution to burning stuff. Batteries were the biggest possible cost, so other forms of storage (heat sinks underground etc) could work out better. But I did read up that Solar uses more carbon in production than it saves in use... and can at times miss energy or economic returns too.

But it is entirely dependent on the sale and install price, along with the expected lifespan. And the stuff I've read relates to industrial/national production not small scale home use...

I use cost amortization for comparison as you probably seen in the pdf document.
As a simple example PV panels cost amortization is 2.4 cent/kWh  (USD) (based on 80 cent/Watt acquisition cost, 25 year amortization period and amount of solar at my location).
petrol for example is now here about 70cent/liter and one liter contains about 9.5kWh of energy/liter so cost is 7.4 cent/KWh significantly higher than PV cost amortization.
This is not all a Gasoline (petrol) burner will not be 100% efficient and be more complex less reliable compared to a simple resistive heat element needed for PV heating and that will make a heater based on petrol significantly more expensive when all that is considered burner, pipes, heat exchanger maybe pumps....
Natural gas is for sure the cheapest form of fossil fuel and that is why I used that in my comparison showing that even that can not compete with direct PV heating and thermal mass storage.

Is extremely wrong to say solar PV panels require more energy to produce than they generate over their life. If that will be true the cost of PV panels will be much higher than it is since you need to pay for that energy when you buy the panel.
The amount of energy used to produce a PV panel can be produced by the panels in just 2 to 4 months. So yes you can build a profitable PV panel factory powered with PV solar energy.

At the utility scale, in places with good solar resource, PV can indeed be cheaper than prevailing sources (gas combined cycle, coal) on a /kWh basis. PV advocates call this "grid parity" -- and it is a real thing. PV is usually not cheaper than wind in windy places, but many places are not suitable for that.

However, you cannot run a power system from PV alone (the sun is intermittent, not dispatchable, and doesn't shine at night), so the /kWh basis is not quite the right way to think about.

Furthermore, there is an interesting phenomenon in places with lots of PV penetration, where the existence of the PV actually makes the output from the gas plant _appear_ more expensive on a /kWh basis. It happens when the owners of a gas- or coal-powered resource needs to recoup the cost of the plant over smaller and smaller kWh sales, because that utility is getting more energy from PV and wind. What's interesting in this case is that the gas or coal plant is still needed (because of flexibility) but much less energy is needed from it.


As for residential solar for heating, why not just heat your storage medium / working fluid directly? Why go through the electrical step? It will make substantially more efficient use of the sunlight. The technology for this has existed for a very long time.

Wind in the end is still solar energy but for small scale even in windy locations like mine are not cost effective when compared to solar PV and they are more intermittent requiring a larger storage capacity.

If you check the document the thing that makes the DMPPT450 cost effective and possible is the combination of cheap PV panels with cheap thermal mass energy storage below 0.5cent/kWh to store energy in thermal mass.
The large thermal mass and large size PV array to provide the house with heating also helps reduce the Lithium battery storage to at least half thus helping also reduce the cost of electrical energy needed for appliances in the house.
I will need no backup energy source for my house and the DMPPT450 + SBMS + PV panels + large thermal storage + small LiFePO4 battery can make a house completely energy independent or a Net Zero energy house at a cost lower than traditional grid electricity + natural gas. For a new house difference is even higher because of the connection cost to those utilities.

The thermal solar was also used in my comparison and that is less cost effective than PV solar heating and less reliable. See page 5 for comparison table.
 

[TechnicalBen]

Yep, sorry, it was the carbon costs that may never balance out, not the electric production (with exception of really small badly made useless stuff ).

[Codebird]

As for residential solar for heating, why not just heat your storage medium / working fluid directly? Why go through the electrical step? It will make substantially more efficient use of the sunlight. The technology for this has existed for a very long time.

I can see one advantage: It's easily added to an existing array. If you already have a sizable PV, it's going to be over-capacity in summer. Once the batteries are full, the panels just sit there being a waste of capital investment. Diverting it into an immersion heater would cost very little (far less than fitting additional solar water heaters and associated plumbing and pump), and would at least take a bit off the gas bill.

[tggzzz]

Don't forget to include the cost of keeping the backup system operational for when the solar/wind/tidal power is unavailable.

[Kleinstein]

It depends on the location on how effective PV is. The return can be about 3 times has high in a really sunny place like souther Spain / the desert SW of the US or inland Australia compared to to a place like England or northern Germany. It also depends o how volatile the sun is - not much fun with PV in the winter in Island (hardly any sun that time of year).

When using PV for an off grid application you will likely have a lot of unused energy in the summer, when you don't need heating and at a cold place still not much cooling either. So for such an application the used PV energy could be something like 1/2 or even less of the theoretical production. It gets even worse if you need extra capacity for bad wether phases if you don't have a lot of storage or a backup system.
The really low price of something like 3-5 cents is for 100% utilization. For a fair comparison one has to include storage and / or limited energy use/demand. So you very could well end up with much higher costs for the storage than for the PV modules.

[Seekonk]

Many years ago I started looking for a community where I could discuss RE ideas.  I've been pushing PV heating for years.  The RE community seems totally oblivious to the energy they waste.  After all it is free. I've heard comments of energy usage actually increasing. While this isn't the norm in the rest of the world, we have water heating tanks.  A small array of 300-600W is sufficient to provide some recovery and all the normal heat loss.  This small cost effective application is the only one that can guarantee 100% of solar energy from the panel is used.  Grid tie seems ideal, but the utilities don't want  you dumping into the grid and that energy is worthless in payback, it will only get worse.

[CJay]

I might be missing something crucial here but:

If it's purely for heating would it not be better to harvest the sunlight using evacuated water heating tubes that can have up to 90% efficient conversion rather than converting it to electricity at some order of magnitude lower efficiency and using that to heat your property?

Sure, you've still got a need for electricity to run pumps, valves etc. but far less of it.

[Seekonk]

That is what they teach you in school, but lacks a sense of reality.  These systems freeze, leak, break down and are complicated to install.  Running a wire is easy. A recent home repair program quoted these systems at $10,000 to 15,000 to just heat daily water.  Every case is different.  I have a summer home and all hot water is PV, my other home is heat pump hot water.

[Kleinstein]

Though simpler technology the solar thermal systems are more complicated to install (tubes instead of wires) and need more maintenance. Efficiency is somewhat higher, but not reaching 90%, more like 50% - as they have difficulties at low intensity and already something like 10% are lost due to reflection. Still you would need something like 2 to 5 times the area with PV.

Well done, they do work well and $10000 would already be a relatively large system. Also the PV system would also need all the water tank and related parts - which is likely included in the $10000 sum. A poor made solar-thermal system can be a maintenance nightmare - I friend just shut down his system, because he needed a new pump and liquid essentially every second year or so. So it did not work, despite of a very sunny place.

[CJay]

Ah so the complexity trade offs and increased maintenance requirements make them more expensive an investment so even though the headline efficiency is much higher than PV, PV wins through reliability if the water system is badly implemented plus you have a simpler option for local energy storage.

Been a long time since I was at school so it's always a learning experience here.

 

[tggzzz]

That is what they teach you in school, but lacks a sense of reality.  These systems freeze, leak, break down and are complicated to install.  Running a wire is easy. A recent home repair program quoted these systems at $10,000 to 15,000 to just heat daily water.  Every case is different.  I have a summer home and all hot water is PV, my other home is heat pump hot water.

Well, of course without imagination you can design expensive systems. OTOH you can often get 80% of the benefit with a small fraction of the cost.

Such "80%" installations: http://www.365ecology.com/shop/solar-water-heater/megasun-200-lt-greece/ feeding one or two taps are commonplace around the mediterranean.

[mtdoc]

That is what they teach you in school, but lacks a sense of reality.  These systems freeze, leak, break down and are complicated to install.  Running a wire is easy. A recent home repair program quoted these systems at $10,000 to 15,000 to just heat daily water.  Every case is different.  I have a summer home and all hot water is PV, my other home is heat pump hot water.

Well, of course without imagination you can design expensive systems. OTOH you can often get 80% of the benefit with a small fraction of the cost.

Such "80%" installations: http://www.365ecology.com/shop/solar-water-heater/megasun-200-lt-greece/ feeding one or two taps are commonplace around the mediterranean.

Whether you can do a simple, low cost direct solar hot water system is site dependent.  A climate where temperatures never drop below freezing presents many options for very simple systems but even these are subject to corrosion issues.  A simple drainback system will work for a location with the occasional freeze but adds a level of complexity. In areas with more regular and deeper freezing the systems get much more complicated.  The points of failure and the need for maintenance quickly goes up.

As others have stated, the reason PV heated water makes sense now is because of the drop in PV panel prices.  PV panels are virtually maintenance free with a lifespan of 25+ years. If one already has a PV electric system and has the real estate (roof or ground mount) to add more panels it is a no brainer to do that and heat water with PV rather than install a separate direct solar water heating system.   

Those with battery based PV systems (off grid or grid tie with backup) can configure their system to divert any excess power (once batteries are topped off) to water heating.  Some of the bettter charge controllers (eg the Midnite Classic) have programmable auxillary outputs that can be easily set up to drive a SSR based on battery SOC to accomplish this.

[electrodacus]

Just launched the Kickstarter a few minutes ago.

Yep, sorry, it was the carbon costs that may never balance out, not the electric production (with exception of really small badly made useless stuff ).

Carbon cost is dependent on the energy source you are using. You can use solar PV to manufacture solar panels.
If you are going to use energy then building solar panels is the best way if carbon cost is important to you.

Don't forget to include the cost of keeping the backup system operational for when the solar/wind/tidal power is unavailable.

I do not need any backup because of the large and inexpensive thermal mass storage.

It depends on the location on how effective PV is. The return can be about 3 times has high in a really sunny place like souther Spain / the desert SW of the US or inland Australia compared to to a place like England or northern Germany. It also depends o how volatile the sun is - not much fun with PV in the winter in Island (hardly any sun that time of year).

When using PV for an off grid application you will likely have a lot of unused energy in the summer, when you don't need heating and at a cold place still not much cooling either. So for such an application the used PV energy could be something like 1/2 or even less of the theoretical production. It gets even worse if you need extra capacity for bad wether phases if you don't have a lot of storage or a backup system.
The really low price of something like 3-5 cents is for 100% utilization. For a fair comparison one has to include storage and / or limited energy use/demand. So you very could well end up with much higher costs for the storage than for the PV modules.

Yes location is important. I live in a very cold location Saskatchewan, Canada but also decently (more than decently) sunny in winter. The advantage of solar is that even in the worst overcast day you still get some energy (you can see a daily energy graph for a full year on my location to get a better idea).
Yes is true about unused energy in offgrid application but including that cost is still better than grid when heating and electricity is combined. And yes in cold places like mine I need no house cooling (if house is properly done there are plenty of houses here with air conditioning) but also winter is longer with 5 to 6 months of heating season.
PV panel amortization cost is 2.4 cent/kWh so even if you use just half of the energy in average over a year that will double the cost of used energy to 4.8cent/kWh still quite decent.
The thermal storage amortization cost is extremely low at just 0.5 cent/kWh so you can have as much capacity as you need depending on your location and amount of sun.
When heating and electricity is combined you oversize first the thermal storage that is the least expensive then PV array and keep the LiFePO4 battery as small as you can get away with since that has a real world cost amortization of 25 cent/kWh and there is nothing better than LiFePO4 for storage.

I might be missing something crucial here but:

If it's purely for heating would it not be better to harvest the sunlight using evacuated water heating tubes that can have up to 90% efficient conversion rather than converting it to electricity at some order of magnitude lower efficiency and using that to heat your property?

Sure, you've still got a need for electricity to run pumps, valves etc. but far less of it.

It is not and in the document I make the case for that comparing PV with thermal solar (evacuated tubes) and Natural gas. Better efficiency does not equate with better cost amortization.

That is what they teach you in school, but lacks a sense of reality.  These systems freeze, leak, break down and are complicated to install.  Running a wire is easy. A recent home repair program quoted these systems at $10,000 to 15,000 to just heat daily water.  Every case is different.  I have a summer home and all hot water is PV, my other home is heat pump hot water.

Yes thermal solar has problems if not properly installed or bad quality parts are used but even if you not include the maintenance and repair cost is still more expensive than PV solar at this point.

I see most of you did not read or look at the pdf that answers all or almost all question posted here but I get that since if you are not that interested in this you do not want to read a 15 page document (mostly graphs not that much text).

The claim is that this is the most cost effective house energy solution at my location and probably many other locations.


   

[tggzzz]

That is what they teach you in school, but lacks a sense of reality.  These systems freeze, leak, break down and are complicated to install.  Running a wire is easy. A recent home repair program quoted these systems at $10,000 to 15,000 to just heat daily water.  Every case is different.  I have a summer home and all hot water is PV, my other home is heat pump hot water.

Well, of course without imagination you can design expensive systems. OTOH you can often get 80% of the benefit with a small fraction of the cost.

Such "80%" installations: http://www.365ecology.com/shop/solar-water-heater/megasun-200-lt-greece/ feeding one or two taps are commonplace around the mediterranean.

Whether you can do a simple, low cost direct solar hot water system is site dependent.  A climate where temperatures never drop below freezing presents many options for very simple systems but even these are subject to corrosion issues. 

Greek beaches this week
http://www.bbc.co.uk/news/world-europe-38550369

And site-specific factors are why unqualified statements shouldn't be made!

[electrodacus]

Greek beaches this week
http://www.bbc.co.uk/news/world-europe-38550369

And site-specific factors are why unqualified statements shouldn't be made!

That will happen but Greece is and will remain a great place for solar energy.
I remember when I visited Greece many houses had hot water heaters on the roof.

[Seekonk]

Least anyone forget it, PV is high quality energy.  You can do something with it in the summer and winter.  What does an evacuated tube get you in the summer?

[coppice]

Least anyone forget it, PV is high quality energy.  You can do something with it in the summer and winter.  What does an evacuated tube get you in the summer?

Baths and showers. Most of the places I know with a high concentration of evacuated tube solar heaters have little need for space heating. They use it exclusively for hot water, which they tend to need more of in hot weather - people sweat more and shower more in hot weather - although the temperature rise they need to achieve at that time is smaller than in cold weather.

[electrodacus]

Least anyone forget it, PV is high quality energy.  You can do something with it in the summer and winter.  What does an evacuated tube get you in the summer?

I think I mentioned this in the pdf.  For my case the extra energy can keep the LiFePO4 battery smaller since the DMPPT can fully charge the battery in an overcast day by redirecting up to the entire heating array to battery charging when needed.
While it is high quality energy is still hard to find a use for so much excess energy in summer.
One thing that I will be using it is to distill water (we drink distilled water about 4 liter/day and at the moment we buy that for $2/day). While just 10% of the energy from all that excess will be needed to distil 4liters/day of water the savings of $2/day over 25 years will add up to $2 x 365 x 25 = $18250 and this saving alone can pay for the entire installation (more actually).
This is a particular case that we can ave by making our own distilled water for drinking but still is just 10% of the excess.
I realy have no other ideas on where I can use the excess in summer that is around 1MWh/month. Even not using the excess at all this is still more cost effective than any other source as seen in the comparison table where excess energy was considered lost/unused.

Sometimes people try so much to use this excess than they end up spending more than if just not using the excess. 

 

[cmhansen]

PV for heating is ideal ok.  Evacuated tubes fall linearly on efficiency if you look at the data (and heat flux formula):
http://www.heliodyne.com/wp-content/uploads/2016/03/Evacuated-Tube-Comp.pdf

More simply CSP at even 200C is still considered 'waste heat' as basically stated earlier and for good reason.  If you want to heat a pool by a degree or two CSP 'waste heat' is probably more efficient, but not if you want a tank of 60C water.  You can of course get relatively 'high-grade' heat through molten salt (and a steam turbine for electricity), but do you want that over PV for home at a higher cost?  No, and if one is simply using heated water as a working fluid, it really is classified as waste heat that isn't even useful for hot water (only as a limited pre-heater).
https://en.wikipedia.org/wiki/Waste_heat#Disposal

I've written a detailed idea before as well about using an extra heatpump to buffer heating or cooling in a tank of water vs batteries - much more direct than geothermal.  This would work as good for non-solar.  It is geothermal except air-source and buffered daily not seasonally.  Peltier is not (yet) good for cooling at <10% efficiency.  In addition for heating, if you had super-icephobicity coating on a heatpump you could use it in colder periods.  Ideally batteries are the best and most direct buffer, we'll replace heatpumps for heating before we do for cooling.

And in fact look at current cost of batteries at nearly $100 / kWh (almost there but it will surely get there soon), at standard 2k cycles this is only $.05 / kWh of battery use.  Panels are looking more like $.01 / kWh now... if you use batteries 2/3 the time you easily see (.01 x3 + .05 x2)/3 = $.04333 average per kWh, grid cost alone exceeds this and 'free fusion' would end up costing more!

And a tricky counter-intuitive bit about amortized cost of the panel not factoring in land cost - tracking actually increases this (for high-insolation areas doubly so!)  The reason is simple that the higher proportion spent at higher temps, the lower the lifespan (degradation per degree rise).  Meaning colder climates with fixed angle have the least normalized temp degradation per kWh produced, and therefor least cost, and since tracking takes more land than fixed per kWh (I think) this is even more in favor of fixed.  (Also consider seasonal tracking is (substantially?) more productive than daily tracking, if highest power per area is needed).

Yes many are told solar takes more energy than it can produce.... though one study I read had solar at 7x, wind something like 21 and nuclear the highest by an order or more).  Plus this will only go way down if we get away from thick silicon wafers.  Here is a fairly current and concrete (not forcasted) estimate of EPBT that shows solar in an even better 'light':
http://www.apricum-group.com/electricity-payback-time-pv-system-facts/
That is 12.5x - 25x total energy payback (including inverters and BOS) over 25 years!  I'm not sure if variable wafer cutting loss is accounted for in that figure, it might assume 'kerfless':
https://www.greentechmedia.com/articles/read/1366-Technologies-to-Build-250MW-Direct-Silicon-Wafer-Factory-in-Upstate
Regardless no dead birds, burning windmills, bad bearings or massive transmissions to overhaul.

[electrodacus]

Thanks for the detailed comment cmhansen

I've written a detailed idea before as well about using an extra heatpump to buffer heating or cooling in a tank of water vs batteries - much more direct than geothermal.  This would work as good for non-solar.  It is geothermal except air-source and buffered daily not seasonally.  Peltier is not (yet) good for cooling at <10% efficiency.  In addition for heating, if you had super-icephobicity coating on a heatpump you could use it in colder periods.  Ideally batteries are the best and most direct buffer, we'll replace heatpumps for heating before we do for cooling.

I considered heat pump before but the PV energy is so cheap that trying to use a heat pump will not make economic sense. It will when compared to battery but not with my method where battery is not used for heating so cost is extremely low.
Peltier is extremely efficient if used properly as a heat pump and I will do probably a youtube video about that soon. Most care about profit so they use the peltier element at full or almost full rated power but if used at just a fraction of the full power the peltier can be extremely efficient so COP of 3 can be obtained with careful design.
Here is the spec http://www.thermonamic.com/TEC1-12706-English.PDF of a very common peltier element that cost maybe 2 or $3 in China. Check last page and you can see when used at 3V will take about 1A so 3W of power and be able to pump about 12W when 10C delta is used. For high delta using two or 3 stages may be needed the COP will still remain the same.
When the peltier element is used close to full power say 12V and higher temp delta then module is an order of magnitude less efficient with COP well below 1
Of course the cost complexity of the cooling with peltier needs to be weighted against very low cost of PV energy and some compromise between cost/complexity and efficiency can be selected.

And in fact look at current cost of batteries at nearly $100 / kWh (almost there but it will surely get there soon), at standard 2k cycles this is only $.05 / kWh of battery use.  Panels are looking more like $.01 / kWh now... if you use batteries 2/3 the time you easily see (.01 x3 + .05 x2)/3 = $.04333 average per kWh, grid cost alone exceeds this and 'free fusion' would end up costing more!

The cost of battery per storage capacity is not a good indication of anything. Also those $100/kWh (I'm sure are more like $200/kWh today) and only have 500 cycles at 100% DOD so please provide a spec and real price if you have something in mind that can be had today.
LiFePO4 are by far the most cost effective for electrical energy storage and the higher energy density cells while make sense in consumer EV for a few reasons are far from cost competitive in therms of energy storage.
Best real life cost amortization for LiFePO4 currently available is around 25 cent/kWh. The theoretical based on simple calculation as the one you did before is much lower but that is not including the battery aging that affects all batteries much more even than cycle life.
My cost amortization for PV panels of 2.4cent/kWh (USD) is based on (80 cent/Watt acquisition cost, 25 years amortization period and amount of solar at my location ).
While is true that you may be able to get better than 80cent/Watt as PV panel acquisition cost (just seen 67cent/Watt in a US online store) and some panel manufacturer warrant power output up to 30 or 35 years and maybe some areas get slightly more solar than my location the 2.4 cent/kWh is still low enough to make my point that solar PV is the lowest cost of energy currently available for powering an individual house.
With the DMPPT450 and SBMS combination the LiFePO4 can get a better cost amortization than 25cent/kWh (when only SBMS is used) close to half maybe as good as 12cent/kWh becose aging will play a lower role since battery will be smaller and more heavily used so it will last less in time but store more energy in that period (will be cycled more).

And a tricky counter-intuitive bit about amortized cost of the panel not factoring in land cost - tracking actually increases this (for high-insolation areas doubly so!)  The reason is simple that the higher proportion spent at higher temps, the lower the lifespan (exponential degradation per degree rise).  Meaning colder climates with fixed angle have the least normalized temp degradation per kWh produced, and therefor least cost, and since tracking takes more land than fixed per kWh (I think) this is even more in favor of fixed.  (Also consider seasonal tracking is (substantially?) more productive than daily tracking, if highest power per area is needed).

Mechanical solar tracking is for sure a long dead technology and best argument for that is to look at all large scale solar PV installations where 95% of them are fixed PV panels with no tracking at all.

Yes many are told solar takes more energy than it can produce.... though one study I read had solar at 7x, wind something like 21 and nuclear the highest by an order or more).  Plus this will only go way down if we get away from thick silicon wafers.  Here is a fairly current and concrete (not forcasted) estimate of EPBT that shows solar in an even better 'light':
http://www.apricum-group.com/electricity-payback-time-pv-system-facts/
That is 12.5x - 25x total energy payback (including inverters and BOS) over 25 years!  I'm not sure if variable wafer cutting loss is accounted for in that figure, it might assume 'kerfless':
https://www.greentechmedia.com/articles/read/1366-Technologies-to-Build-250MW-Direct-Silicon-Wafer-Factory-in-Upstate
Regardless no dead birds, burning windmills, bad bearings or massive transmissions to overhaul.

That is a false information solar PV can not take more energy to manufacture than it produces over is life.
Think about this way any solar PV manufacturer wants to have a profit and will buy energy in order to produce the panels.
Then you pay the cost of production (energy + materials + equipment + labor) + manufacturer profit + reseller profit + taxes.
A simple 250W PV panel can be had easy for $200
This panel will produce 380kWh/year at my location (an average location for solar nothing special).
So say just 25 years (panels can last and produce energy a lot longer) x 380kWh/year  = 9.5MWh of energy produced by that panel over is 25 years life.

$200/9500kWh = $0.021/kWh so I also calculated the cost amortization. For solar data go to PVWatt select Regina Saskatchewan, Canada as my location use panel tilt at 50 degree and 1kW PV array since it will not accept smaller then get than energy for a year and divide by 4 for a 250W panel and you will get that 380kWh number.

Now I'm extremely sure that PV panel total energy used will not be anywhere near 9.5MWh for a producing ans shipping a single panel and is probably more like the energy can be recovered in just the fist few months by the panel.
Do not forget that the cost of the PV panel includes so much more than just the energy used to manufacture and transport the panel. 

[splin]

Check last page and you can see when used at 3V will take about 1A so 3W of power and be able to pump about 12W when 10C delta is used. For high delta using two or 3 stages may be needed the COP will still remain the same.

No. For the second stage you need to provide another 3W of power to move the same 12W through another 10C delta. Plus an additional 3/12 * 3W to move the power added in the first stage, so the overall COP is now less than half that of the first stage. You end up with much the same COP as if you used a single stage. For large deltas, > 40C or so, you are forced to use multiple stages but the COP is terrible.

[electrodacus]

Check last page and you can see when used at 3V will take about 1A so 3W of power and be able to pump about 12W when 10C delta is used. For high delta using two or 3 stages may be needed the COP will still remain the same.

No. For the second stage you need to provide another 3W of power to move the same 12W through another 10C delta. Plus an additional 3/12 * 3W to move the power added in the first stage, so the overall COP is now less than half that of the first stage. You end up with much the same COP as if you used a single stage. For large deltas, > 40C or so, you are forced to use multiple stages but the COP is terrible.

You do not move the same 12W you move additional 12W.
Second stage will of course need to be a bit more powerful since it will need to move the 12W + 3W from the hot side of the first stage.
You forget that you get a 10C delta with single stage and 20C delta with two stage so is obviously more energy pumped.

[tszaboo]

If you can get "infinite amount" of not frozen water then a heat pump will be more effective than direct heating. Of course you need to step away from Peltier, that will be very expensive. Traditional systems use the same methods as refrigerators.
Also, I dont know how do you "feel" the cold or warmth in Canada. I have the issue, that I feel cold in a room if there isnt a warm radiator in the room, even if the room air is 20+ degrees warm. Its the infrared radiation of course.

Also, there are a lot of development for gas generators. They use the gas to generate electicity and heat, increasing the efficiency of the system. I believe it will be standard in the future, replacing every gas heating system.
https://en.wikipedia.org/wiki/Micro_combined_heat_and_power
Sure, it is still powered by dinosaurs fart, and not green.

Otherwise, I like the designs you are doing. There arent too many solar open source projects.

[splin]

Check last page and you can see when used at 3V will take about 1A so 3W of power and be able to pump about 12W when 10C delta is used. For high delta using two or 3 stages may be needed the COP will still remain the same.

No. For the second stage you need to provide another 3W of power to move the same 12W through another 10C delta. Plus an additional 3/12 * 3W to move the power added in the first stage, so the overall COP is now less than half that of the first stage. You end up with much the same COP as if you used a single stage. For large deltas, > 40C or so, you are forced to use multiple stages but the COP is terrible.

You do not move the same 12W you move additional 12W.
Second stage will of course need to be a bit more powerful since it will need to move the 12W + 3W from the hot side of the first stage.

No you're not moving an additional 12W - after all where is it supposed to have come from? The two stages are in series so the output from the second stage is the 12W transferred by the first stage from the object being cooled plus the I^2R losses of both stages.

Take a look at page 11 of http://www.pathways.cu.edu.eg/ec/text-pdf/part%20c-17.pdf to see the overall COP of single and multi-stage peltier coolers against temperature differences. Its not a very good quality diagram but its very clear that COP declines dramatically with increasing delta T no matter how many stages you use.

If you want the equations you can find them here: https://thermal.ferrotec.com/technology/thermoelectric-reference-guide/thermalref12/

Note in particular the equations for the amount of heat pumped for both a two stage and three stage cooler are identical - 12.2.1 b) and 12.2.2 c) being that pumped by the smallest module in both cases.

You forget that you get a 10C delta with single stage and 20C delta with two stage so is obviously more energy pumped.

No I didn't forget and its not obvious. A higher delta T does not mean that more energy is pumped. A single peltier can pump the same amount of heat, Qc (Watts), to different delta Ts but the COP reduces with increasing delta T.

[electrodacus]

If you can get "infinite amount" of not frozen water then a heat pump will be more effective than direct heating. Of course you need to step away from Peltier, that will be very expensive. Traditional systems use the same methods as refrigerators.
Also, I dont know how do you "feel" the cold or warmth in Canada. I have the issue, that I feel cold in a room if there isnt a warm radiator in the room, even if the room air is 20+ degrees warm. Its the infrared radiation of course.

Also, there are a lot of development for gas generators. They use the gas to generate electicity and heat, increasing the efficiency of the system. I believe it will be standard in the future, replacing every gas heating system.
https://en.wikipedia.org/wiki/Micro_combined_heat_and_power
Sure, it is still powered by dinosaurs fart, and not green.

Otherwise, I like the designs you are doing. There arent too many solar open source projects.

As you maybe seen in my presentation page 5 where I compare my solution with thermal solar and natural gas and both of those solutions are more expensive (and I was generous).
Geothermal and heat pump are also a way more expensive solution and I can get in to the detail if you want but basically the cost for unit of energy for direct PV heating (the solution I propose) is so low that you can not cost amortize the equipment needed even for an air heat pump much less a geothermal installation. Of course air heatpump will not work here since is way to cold.
That electricity generation and using the heat loss for heating was used for quite some time especially in East Europe from where I'm originally. The small electrical generators usually run on natural gas where also distributing the hot water and heating to the surrounding building.
There is no extra advantage there and that solution will be still much more expensive than PV solar direct heating plus electricity in most places around the world. The factor is just the amount of sun at that location and the cost of natural gas.
I do not insist much on the green part since my solution is cost effective compared to any other solution.
Traditionally natural gas was the cheapest form of energy that is why more than half of the buildings around the world are heated with natural gas but that is not the case anymore and PV solar direct heating is more cost effective.
   

[electrodacus]

Check last page and you can see when used at 3V will take about 1A so 3W of power and be able to pump about 12W when 10C delta is used. For high delta using two or 3 stages may be needed the COP will still remain the same.

No. For the second stage you need to provide another 3W of power to move the same 12W through another 10C delta. Plus an additional 3/12 * 3W to move the power added in the first stage, so the overall COP is now less than half that of the first stage. You end up with much the same COP as if you used a single stage. For large deltas, > 40C or so, you are forced to use multiple stages but the COP is terrible.

You do not move the same 12W you move additional 12W.
Second stage will of course need to be a bit more powerful since it will need to move the 12W + 3W from the hot side of the first stage.

No you're not moving an additional 12W - after all where is it supposed to have come from? The two stages are in series so the output from the second stage is the 12W transferred by the first stage from the object being cooled plus the I^2R losses of both stages.

Take a look at page 11 of http://www.pathways.cu.edu.eg/ec/text-pdf/part%20c-17.pdf to see the overall COP of single and multi-stage peltier coolers against temperature differences. Its not a very good quality diagram but its very clear that COP declines dramatically with increasing delta T no matter how many stages you use.

If you want the equations you can find them here: https://thermal.ferrotec.com/technology/thermoelectric-reference-guide/thermalref12/

Note in particular the equations for the amount of heat pumped for both a two stage and three stage cooler are identical - 12.2.1 b) and 12.2.2 c) being that pumped by the smallest module in both cases.

You forget that you get a 10C delta with single stage and 20C delta with two stage so is obviously more energy pumped.

No I didn't forget and its not obvious. A higher delta T does not mean that more energy is pumped. A single peltier can pump the same amount of heat, Qc (Watts), to different delta Ts but the COP reduces with increasing delta T.

Not sure what sort of analogy to make to explain this.
I will try with water pumps

Imagine you have two 100% efficient 12W water pumps and each can move X amount of water/minute at the height H
Then what you can do is to have them in parallel so they will move 2X amount of water at height H so total work done is two times higher.
Then imagine you have the first pump at first floor pumping X amount of water at first level ho height H and then second pump will be at the second level and move that to next level so total height is 2H but just X amount of water.

Now question is what is the equivalent efficiency of those pumps working together in first case with pumps in parallel and then in second case with pumps in series.
For me the answer is obvious in both cases there where 24W used and 24W of work done so in both cases the efficiency is 100%

Hope my analogy worked but yes the temperature (equivalent with height in the analogy) is important.

[splin]

Not sure what sort of analogy to make to explain this.
I will try with water pumps

Imagine you have two 100% efficient 12W water pumps and each can move X amount of water/minute at the height H
Then what you can do is to have them in parallel so they will move 2X amount of water at height H so total work done is two times higher.
Then imagine you have the first pump at first floor pumping X amount of water at first level ho height H and then second pump will be at the second level and move that to next level so total height is 2H but just X amount of water.

Now question is what is the equivalent efficiency of those pumps working together in first case with pumps in parallel and then in second case with pumps in series.
For me the answer is obvious in both cases there where 24W used and 24W of work done so in both cases the efficiency is 100%

Hope my analogy worked but yes the temperature (equivalent with height in the analogy) is important.

OK I think I understand where you are coming from but your analogy isn't useful - the work done by the 100% efficient pumps is equal to the electrical energy you provide to run them whereas the point of using a heat pump is to get more energy out than the electrical energy supplied - by transferring free low grade heat energy into more useful higher temperature energy.

What you are missing is that a peltier isn't doing any work - it merely moves energy from the low temperature side to the other, higher temperature side. The energy coming out the high side is equal to that moved from the low side plus the resistive heating losses incurred. Higher temperature out means the energy is more useful to you but it doesn't mean it provides more energy simply because it is hotter. A resistive heating element can create heat energy at any temperature you like (until it melts) but the heat energy won't exceed the electrical energy you input.

When you have a stack of peltiers the total heat output is the heat moved from the cold side of the first element plus the total losses in all the peltiers. So after a few stages, virtually all the heat being transferred is the heat created by the resistive losses in the preceding peltier stages, such that there is very little gain over using a resistive heater set to produce the desired temperature.

The conventional definition of overall COP for a multi-stage peltier is the amount of heat transferred from the cold side of the first stage divided by the total amount of power used. But in your case the total heat out is useful so a more relevant COP definition is the total amount of heat output divided by total electrical power used (assuming the heat transferred from the source by the first stage is 'free'). The attached shows a spreadsheet showing how the COP reduces as more stages are added, assuming each stage is scaled appropriately.

[Edit] Attached spreadsheet as well

[Kleinstein]

Besides the poor efficiency, TEC have another problem: the efficiency goes down even more if not used at the suitable current level for the temperature difference and there is quite some heat flow if turned off. This is especially a problem with volatile energy supply. So you would need a kind of thermal switch, like a fluid circuit with a pump - just the thing you wanted to avoid with the TEC.

[electrodacus]

OK I think I understand where you are coming from but your analogy isn't useful - the work done by the 100% efficient pumps is equal to the electrical energy you provide to run them whereas the point of using a heat pump is to get more energy out than the electrical energy supplied - by transferring free low grade heat energy into more useful higher temperature energy.

What you are missing is that a peltier isn't doing any work - it merely moves energy from the low temperature side to the other, higher temperature side. The energy coming out the high side is equal to that moved from the low side plus the resistive heating losses incurred. Higher temperature out means the energy is more useful to you but it doesn't mean it provides more energy simply because it is hotter. A resistive heating element can create heat energy at any temperature you like (until it melts) but the heat energy won't exceed the electrical energy you input.

When you have a stack of peltiers the total heat output is the heat moved from the cold side of the first element plus the total losses in all the peltiers. So after a few stages, virtually all the heat being transferred is the heat created by the resistive losses in the preceding peltier stages, such that there is very little gain over using a resistive heater set to produce the desired temperature.

The conventional definition of overall COP for a multi-stage peltier is the amount of heat transferred from the cold side of the first stage divided by the total amount of power used. But in your case the total heat out is useful so a more relevant COP definition is the total amount of heat output divided by total electrical power used (assuming the heat transferred from the source by the first stage is 'free'). The attached shows a spreadsheet showing how the COP reduces as more stages are added, assuming each stage is scaled appropriately.

I see so you think my analogy with water pumps is not applicable here.

I will try an example and please point out where you think I'm wrong.

I have one of those peltier elements mentioned before and it is on the cold side glued to a water cooling block while on the hot side is glued to say a huge copper cube (just for simplicity so that hot side temperature remains fixed and block will be at +27°C).
Now I have two buckets one is full of water at +27°C and the other is empty and I want to cool that water to +17°C an put that cold water in the empty bucket.
So there will be a variable speed pump pumping water from the full bucket to the empty bucket trough the water cooling block.
Since I will be supplying this peltier element with 3V and based on the graph it looks like it will be able to pump about 12W from the cold side and from the other graph COP is about 3.25 thus 12W/3.25 = 3.69W are used by peltier element so around 1.23A x 3V
Now we know that to change the temperature of one liter of water by one degree Celsius we need about 1.2Wh of energy and since our heat pump (peltier element) can move 12W and what we want is to reduce the water temperature by a 10 degree Celsius delta so we can calculate the appropriate flow rate required so that water is cooled to exactly +17°C
(1.2Wh per liter per degree Celsius x 10°C )/ 12W = 1 liter/hour and this will be the flow rate required.

Maybe you see where this is going
Adding a second peltier between the hot side of the first and the huge copper block you reduce the water temperature by 20°C thus twice the amount of energy is transferred to water.
So COP will be the average of the two stages and if both have a COP of 3.25 then total COP of two stages will still be the same 3.25

I know you will need to add the additional 3.69W to the cold side and the second stage will need to pump 12W + 3.69W = 15.69W so if same type peltier element will be used then it will have a slightly lower COP but you can also select a slightly larger peltier element so that you can maintain the same COP of 3.25

[splin]

I will try an example and please point out where you think I'm wrong.

I have one of those peltier elements mentioned before and it is on the cold side glued to a water cooling block while on the hot side is glued to say a huge copper cube (just for simplicity so that hot side temperature remains fixed and block will be at +27°C).
Now I have two buckets one is full of water at +27°C and the other is empty and I want to cool that water to +17°C an put that cold water in the empty bucket.
So there will be a variable speed pump pumping water from the full bucket to the empty bucket trough the water cooling block.
Since I will be supplying this peltier element with 3V and based on the graph it looks like it will be able to pump about 12W from the cold side and from the other graph COP is about 3.25 thus 12W/3.25 = 3.69W are used by peltier element so around 1.23A x 3V
Now we know that to change the temperature of one liter of water by one degree Celsius we need about 1.2Wh of energy and since our heat pump (peltier element) can move 12W and what we want is to reduce the water temperature by a 10 degree Celsius delta so we can calculate the appropriate flow rate required so that water is cooled to exactly +17°C
(1.2Wh per liter per degree Celsius x 10°C )/ 12W = 1 liter/hour and this will be the flow rate required.

Maybe you see where this is going

Adding a second peltier between the hot side of the first and the huge copper block you reduce the water temperature by 20°C thus twice the amount of energy is transferred to water.

No - if you don't increase the voltage to the first peltier it willl still only pump 12W with a 10C delta. That's where you have been going wrong. The water can now be cooled by 20C but the flow rate will have to be halved to .5l/hr. As you say, the second peltier will move 12W + 3.69W, requiring 4.83W (at a COP of 3.25) so outputing 20.52W to the copper block. Total electricity supplied is 3.69W + 4.83 = 8.52W

So COP will be the average of the two stages and if both have a COP of 3.25 then total COP of two stages will still be the same 3.25

No the overall COP will be 12W/8.52 = 1.41. Alternatively you get 20.52W of heat out for your 8.52W electrical input or 2.41x which isn't bad.

In reality other losses, such as heat leaking from the hot side of the peltier to the cold side through the insulation around them and the screws required to apply the necessary clamping forces between the heatsinks and peltiers will reduce these efficiencies.

Additional losses arise from the thermal resistances between the peltiers and the heatsinks, between adjacent peltiers and especially between the heatsinks and the source and destination mediums (eg. water or air) will also reduce the COP as the delta C seen by the peltiers will be higher than between the source and destination.

[electrodacus]

No - if you don't increase the voltage to the first peltier it willl still only pump 12W with a 10C delta. That's where you have been going wrong. The water can now be cooled by 20C but the flow rate will have to be halved to .5l/hr. As you say, the second peltier will move 12W + 3.69W, requiring 4.83W (at a COP of 3.25) so outputing 20.52W to the copper block. Total electricity supplied is 3.69W + 4.83 = 8.52W

I know I'm not great at explaining things but I was sure my example was quite clear.
When I added the second peltier element the hot side of the first peltier element has dropped from +27°C to +17°C provided by the cold side of the second peltier.
Each peltier element will pump around 12W (ignoring those IR losses) and those add up if the hot face of the first peltier is in contact with the cold face of the second one.
Same as if you inverse the current flow on one of the peltier you cancel the work of the first one.
So you either have the Qc1 + Qc2 or Qc1 - Qc2 and in case Qc1=Qc2 the you have either 2xQc or you have zero in the second case.
If you have two of those cheap peltier module you can do the experiment but is not necessary since it should be obvious.

I'm an EE so my knowledge of thermodynamics is limited but I'm smart enough so that if I'm wrong you will be able to explain where I'm wrong to me and so far I see no problems with my understanding of how a two stage heat pump will work.
I also have no problem admiring when I'm wrong since that is not something uncommon.

I also think my first analogy with water pumps was not that bad so you should look at that one again if you still do not get what I'm saying.
The height delta there is the equivalent of temperature delta here.
With the first stage you do half of the work by moving 12W of heat and with the second stage you take that work already done and move another 12W.
So in the example with one stage you will be able to cool 1liter of water with 10°C lower than hot side you can call that ambient (the huge copper cube so that the small energy transferred will not influence the cube temperature).
When you add the second stage that has sufficient power pumped to cool the hot side of the first stage 10°C lover than the huge copper cube it is almost like if there was a single stage but the copper cube had just +17°C instead of +27°C

[splin]

No - if you don't increase the voltage to the first peltier it willl still only pump 12W with a 10C delta. That's where you have been going wrong. The water can now be cooled by 20C but the flow rate will have to be halved to .5l/hr. As you say, the second peltier will move 12W + 3.69W, requiring 4.83W (at a COP of 3.25) so outputing 20.52W to the copper block. Total electricity supplied is 3.69W + 4.83 = 8.52W

I know I'm not great at explaining things but I was sure my example was quite clear.

Your example was clear enough, it was just that you made a mistake when you analysed the effect of the second peltier.

When I added the second peltier element the hot side of the first peltier element has dropped from +27°C to +17°C provided by the cold side of the second peltier.
Each peltier element will pump around 12W (ignoring those IR losses) and those add up if the hot face of the first peltier is in contact with the cold face of the second one.

Yes but the bit you keep missing is that they are the same 12Ws so they don't add up.

Same as if you inverse the current flow on one of the peltier you cancel the work of the first one.
So you either have the Qc1 + Qc2 or Qc1 - Qc2 and in case Qc1=Qc2 the you have either 2xQc or you have zero in the second case.
If you have two of those cheap peltier module you can do the experiment but is not necessary since it should be obvious.

The peltiers don't generate any power - ignoring their I^2R and thermal resistance losses, they simply transfer the power that's passed to their cold side to the hot side but increases the temperature. Higher temperature does not equate to more energy or power out than was put in. So if you have 5 in series you still only get 12W out of the hot side - each peltier passing on the 12W whilst increasing the temperature by 10C. The 12W that comes out of the last was the 12W that was passed into the first from the water. An analogy is a human chain passing along a bucket of water, where each person heats up the water by 10C but pours some away before passing on exactly the same thermal energy they received.  Alternatively the first person gets a load of paralleled batteries. They rearrange the batteries so some are in series and passes it on. The total energy in the batteries doesn't change but the output voltage increases at each step. So you don't get QC1 + QC2, you get QC1 only.

They don't remove or destroy energy or power either so QC1 - QC2 != 0. If you reverse the second, both will pump heat from their cold faces to the joined hot sides. That heat would have nowhere to go so the hot sides will get hotter and hotter until they destroy themselves. As the hot side gets hotter, and their cold sides remain at constant temperature, their COP reduce and the amount of heat they pump will reduce but not probably not enough to avoid damage. Consider this configuration as two peltiers in parallel with their hot sides connected to a common (very poor) heatsink but their cold sides connected to heatsinks at different temperatures and thus operating at different delta-T.

I'm an EE so my knowledge of thermodynamics is limited but I'm smart enough so that if I'm wrong you will be able to explain where I'm wrong to me and so far I see no problems with my understanding of how a two stage heat pump will work.
I also have no problem admiring when I'm wrong since that is not something uncommon.

I expect that's more likely to be one of D. Trump's many interesting characteristics 

I also think my first analogy with water pumps was not that bad so you should look at that one again if you still do not get what I'm saying.
The height delta there is the equivalent of temperature delta here.

In your analogy the water gains height and thus potential energy. Peltiers increase the temperature but don't increase the energy. Consider them more like transformers which change the voltage but not the power of a signal. 

With the first stage you do half of the work by moving 12W of heat and with the second stage you take that work already done and move another 12W.

Not another 12W, the same 12W. The second peltier can't pump another 12W as the only heat available for it to pump is that delivered by the first. It can't create energy, it can only move it from the cold side to the hot side whilst transforming the temperature.

So the total output is 12W plus the heat losses in the peltiers. It's really quite simple to calculate the COP - its the total heat moved from the input, cold side divided by the amount of electrical power used. The COP usually shown in peltier datasheets relevant for cooling performance where the heat out is a waste product and is better described as COPcooling. In cases like yours where the heat out is what you are after, COPheating is relevant and is the total heat delivered to the hot side dived by the electrical power used.

With one peltier  the output is 12W + 3.69W              = 15.69W; COPc = 12/3.69      = 3.25; COPh = 15.69/3.69 = 4.25
With two peltiers the output is 12W + 3.69W + 4.83W = 20.52W; COPc = 12W/(8.52) = 1.41; COPh = 20.52/8.52 = 2.41

The COP almost halve when delta T doubles from 10 to 20C

For an EE analogy consider a 12W, 12V 1A power supply driving a 12W constant power load. The power supply is the 12W that comes from your cold water, the voltage is analogous to the water temperature. Now add two 100% efficient 10V voltage boost convertors in series. The output voltage is now 32V but it still can only deliver 12W. The voltage/temperature has been increased by the boosters/peltiers but they don't add or subtract any energy/power.

To model the peltier I^2R losses, add constant power, power supplies in series with the output of each booster, the first set to 3.69W and the second to 4.83W. Reduce the boost voltages so that each stage still only increases the voltage by 10V (so the output is still 32V) and increase the load's power to 20.52W.[/quote]

So in the example with one stage you will be able to cool 1liter of water with 10°C lower than hot side you can call that ambient (the huge copper cube so that the small energy transferred will not influence the cube temperature).
When you add the second stage that has sufficient power pumped to cool the hot side of the first stage 10°C lover than the huge copper cube it is almost like if there was a single stage but the copper cube had just +17°C instead of +27°C

Yes the water will be 10C below ambient with one stage, 20C below with two stages. But the energy extracted from the water will be exactly the same in both cases - 12W - so you will have half the quantity of water in the second case after any given amount of time.

Hope that helps.

[electrodacus]

Yes the water will be 10C below ambient with one stage, 20C below with two stages. But the energy extracted from the water will be exactly the same in both cases - 12W - so you will have half the quantity of water in the second case after any given amount of time.

I can think on one more simplification for you to understand this.

Same example single stage on the hot side is the +27°C  huge copper cube and water is also +27°C  then I can cool water flowing at the rate of 1 liter/hour to +17°C  power transferred from water 12W
Now what you do is replace that huge copper cube with a similar one but this time the cube is at just +17°C so now you can cool water flowing at the same rate of 1liter/hour to +7°C so power transferred from water 24W

If you can agree with the above then second stage will do the exact same thing keeping the hot side of the first stage 10°C lower than the original copper cube so +17C.

[ez24]

How about add your youtube link to your profile like your web address (which seems also not to have a YT link)

Also I suggest you make a post with links to other YT reviewers on your project

Can I add you to this list:

https://www.eevblog.com/forum/other-blog-specific/dd/msg1093983/#msg1093983

[electrodacus]

How about add your youtube link to your profile like your web address (which seems also not to have a YT link)

Also I suggest you make a post with links to other YT reviewers on your project

Can I add you to this list:

https://www.eevblog.com/forum/other-blog-specific/dd/msg1093983/#msg1093983

Thanks for the suggestion, I just made the change to my profile.
Yes you can add me to that list, I had no idea that list existed.
My projects are fairly low volume so only Martin ( mjlorton ) and Julian Ilett made video reviews about my Solar BMS.
Maybe when I have the new SBMS and DMPPT ready will send a sample to Dave also.

[Someone]

Yes the water will be 10C below ambient with one stage, 20C below with two stages. But the energy extracted from the water will be exactly the same in both cases - 12W - so you will have half the quantity of water in the second case after any given amount of time.

I can think on one more simplification for you to understand this.

Same example single stage on the hot side is the +27°C  huge copper cube and water is also +27°C  then I can cool water flowing at the rate of 1 liter/hour to +17°C  power transferred from water 12W
Now what you do is replace that huge copper cube with a similar one but this time the cube is at just +17°C so now you can cool water flowing at the same rate of 1liter/hour to +7°C so power transferred from water 24W

If you can agree with the above then second stage will do the exact same thing keeping the hot side of the first stage 10°C lower than the original copper cube so +17C.

Or we can bring it back to electrical theory, first eliminating the concept of two bodies at constant temperature. Take some given temperature as your environment being a large thermal mass which you cannot materially effect. When you move thermal energy to or from this environmental temperature to something else the something else has an impedance (insulation from) to the environment so it cannot be an arbitrary temperature difference without a source of energy to keep it there.

Now the fun bit, when you model the peltier element thermal system with the electrical analogy it has the characteristics of a voltage source (the temperature difference) and then a current source pouring the thermal energy dissipated in the operation of the peltier back into the hot side:
http://www4.ee.bgu.ac.il/~pel/pdf-files/conf105.pdf
Its the addition of these dissipations at each stacked stage that cause the loss of performance, as each subsequent hotter peltier is supporting/carrying the thermal load of all of those above. Like supporting a pyramid you often see stacked peltier stages having successively smaller peltiers as the hottest end is pushing a lot more thermal power through it.

[splin]

Yes the water will be 10C below ambient with one stage, 20C below with two stages. But the energy extracted from the water will be exactly the same in both cases - 12W - so you will have half the quantity of water in the second case after any given amount of time.

I can think on one more simplification for you to understand this.

Same example single stage on the hot side is the +27°C  huge copper cube and water is also +27°C  then I can cool water flowing at the rate of 1 liter/hour to +17°C  power transferred from water 12W
Now what you do is replace that huge copper cube with a similar one but this time the cube is at just +17°C so now you can cool water flowing at the same rate of 1liter/hour to +7°C so power transferred from water 24W

If you can agree with the above then second stage will do the exact same thing keeping the hot side of the first stage 10°C lower than the original copper cube so +17C.

Sigh; one last try but I'm beginning to wonder if you actually read any of my previous posts.

Consider it slightly differently, again assuming 100% efficient peltiers. Take water from a lake containing water at 7C which is pumped through a 100% efficient heatsink which keeps the cold side of a peltier at a constant 7C. The hot side is attached to a large copper mass at a constant 17C. The peltier is driven at 3V and is sized to pump 12W from the lake water to the copper mass given the delta T of 10C. I'm sure we agree so far.

The 12W is determined *only* by the characteristics of the particular peltier, the driving voltage and delta T - it can be read from the graphs in the datasheet.

Now replace the 17C copper mass by a second peltier which has another copper mass at 27C. The second peltier will also have a delta T of 10C and because it is the same size and is also driven at 3V will also pump 12W from the cold to hot side. Which is convenient because that is exactly how much  power is being received from the first. The key fact is that the first peltier cannot tell the difference between the two scenarios and doesn't care. In both cases it is driven at 3V and sees a delta T of 10C so pumps 12W from the lake water to whatever is on the hot side. It won't start extracting 24W from the water as you keep suggesting as it doesn't know that anything changed between the first and scenario.

The only difference is the temperature of the final hot side but the rate that heat energy is transferred from the lake water, 12W, is the same in both cases.

[tszaboo]

The only difference is the temperature of the final hot side but the rate that heat energy is transferred from the lake water, 12W, is the same in both cases.

Energy is measured in Joules, or calories, not watts. Heating up 1 gram of water 10 degrees is 10 cal, heating it up 20 degrees is 20 cal. The first system only heats up 10 degrees, the second 20. Hence the second system delivers more energy.
The peltier is actually not going to be "100% efficient". It is not efficiency. The same way as a fuel tanker, moving a 10 tons of fuel, and just using 100Kg is not going to be 10000% "efficient". So stop thinking about it that way.

[electrodacus]

The only difference is the temperature of the final hot side but the rate that heat energy is transferred from the lake water, 12W, is the same in both cases.

Energy is measured in Joules, or calories, not watts. Heating up 1 gram of water 10 degrees is 10 cal, heating it up 20 degrees is 20 cal. The first system only heats up 10 degrees, the second 20. Hence the second system delivers more energy.
The peltier is actually not going to be "100% efficient". It is not efficiency. The same way as a fuel tanker, moving a 10 tons of fuel, and just using 100Kg is not going to be 10000% "efficient". So stop thinking about it that way.

Thanks for getting involved.
If you are able to convince him with this short explanation then you are an excellent communicator
While all you are saying is completely correct I will prefer if you where not using Joules or calories for energy and instead use Watt second or Watt hour 1Joule = 1Ws = 1/3600Wh
For all involved in electronics Wh is a more meaningful unit for energy. (at least that is my personal opinion)

[electrodacus]

Sigh; one last try but I'm beginning to wonder if you actually read any of my previous posts.

Consider it slightly differently, again assuming 100% efficient peltiers. Take water from a lake containing water at 7C which is pumped through a 100% efficient heatsink which keeps the cold side of a peltier at a constant 7C. The hot side is attached to a large copper mass at a constant 17C. The peltier is driven at 3V and is sized to pump 12W from the lake water to the copper mass given the delta T of 10C. I'm sure we agree so far.

The 12W is determined *only* by the characteristics of the particular peltier, the driving voltage and delta T - it can be read from the graphs in the datasheet.

Now replace the 17C copper mass by a second peltier which has another copper mass at 27C. The second peltier will also have a delta T of 10C and because it is the same size and is also driven at 3V will also pump 12W from the cold to hot side. Which is convenient because that is exactly how much  power is being received from the first. The key fact is that the first peltier cannot tell the difference between the two scenarios and doesn't care. In both cases it is driven at 3V and sees a delta T of 10C so pumps 12W from the lake water to whatever is on the hot side. It won't start extracting 24W from the water as you keep suggesting as it doesn't know that anything changed between the first and scenario.

The only difference is the temperature of the final hot side but the rate that heat energy is transferred from the lake water, 12W, is the same in both cases.

I do of course read all that you are writing since I try to understand how I can better explain to you where you are wrong.
But maybe you already realized where you made the mistake.

Original question was the COP for two staked (as in serial thermal connection) heat pumps.
If for simplification both stages operate at a COP of 3 the total COP of the two stage system will also be 3

And to answer your question. Yes in your example with two stage the system will move 24W from the lake water to the large copper mass (not sure why you got complicated with the lake when you could have used another large copper cube on the cold side also).

Still my example with the 1liter/hour flow was better since cooling that 1 liter of water by 10C will equate with 12Wh of energy while cooling the same 1 liter of water by 20C will equate with 24Wh of energy.
That 1 liter of water siting at 10C lower than ambient will have a 12Wh stored and if is 20C lower than ambient it has 24Wh energy stored. So while that water will get back to ambient  temperature will transfer that amount of energy to ambient.

This makes Peltier elements fairly efficient if properly used. I just think many people have misconception about peltier elements in therms of COP because most if not all designs optimize for cost and not COP and then COP is realy bad below 0.5 in most of this applications. 

[Kleinstein]

.....
This makes Peltier elements fairly efficient if properly used. I just think many people have misconception about peltier elements in therms of COP because most if not all designs optimize for cost and not COP and then COP is realy bad below 0.5 in most of this applications.

No: Peltier elements are rather low efficiency. The best (not the cheap Chinese ones) ones are something like 15% of the thermodynamic limit, while conventional ones get something like 50% of that limit, sometimes more.

A TEC can get a high COP - but this is only at very low temperature difference (e.g. < 10 K). To be useful for heating, one would need to move heat from near 0 C to something like 30 C. At a 30 C difference the COP of an TEC is more like 1.5 at best. Stacking several TECs is not helping much at this low temperature difference - in theory it might help a little (like a few percent), but in practice things likely get worse due to thermal resistance.

So a COP of 3 at 10 K might be really good for a TEC, but it is still not competitive, as at such a low temperature difference conventional heat pumps could give you a COP of maybe 10 or 15.

The TEC specs are sometimes a little misleading, as they are for the limiting case of zero or maximum temperature difference. For best efficiency one would have to use lower current and thus also reduce the power per unit and thus increase the specific costs.

@electrodacus: if you are looking for mistakes - read your own texts too.

[electrodacus]

No: Peltier elements are rather low efficiency. The best (not the cheap Chinese ones) ones are something like 15% of the thermodynamic limit, while conventional ones get something like 50% of that limit, sometimes more.

A TEC can get a high COP - but this is only at very low temperature difference (e.g. < 10 K). To be useful for heating, one would need to move heat from near 0 C to something like 30 C. At a 30 C difference the COP of an TEC is more like 1.5 at best. Stacking several TECs is not helping much at this low temperature difference - in theory it might help a little (like a few percent), but in practice things likely get worse due to thermal resistance.

So a COP of 3 at 10 K might be really good for a TEC, but it is still not competitive, as at such a low temperature difference conventional heat pumps could give you a COP of maybe 10 or 15.

The TEC specs are sometimes a little misleading, as they are for the limiting case of zero or maximum temperature difference. For best efficiency one would have to use lower current and thus also reduce the power per unit and thus increase the specific costs.

TEC are solid state so very reliable.
You can stack TEC modules to increase the temperature delta while maintaining high COP.
Yes cost will increase but you can get a TEC module now for $2 or $3 (that is what I paid a few years ago did not checked now).
And yes a compressor based heatpump can have a higher efficiency but as I mentioned I prefer the solid state reliability of TEC.
Based on the cost of raw materials TEC should be less expensive than compressor based so is maybe just about the production volume.

@electrodacus: if you are looking for mistakes - read your own texts too.

If you are referring to grammar then you are right there are sure plenty of mistakes and if you are referring to technical mistakes then please point out where.

[polowcz]

how about a system combined from PV doing electrolysis of a water down to oxygen and hydrogen during the day (sun presence) and for nights using a fuel cell? would this system be technically/economically possible for wide presence? Benefits are well known since Apollo programme - electricity, (hot) water and no pollution...

BR
Paul

[Seekonk]

Speaking of efficiency, I'd like to know how you PWM a battery off the same panels you power point the resistive heaters.  It seems you can be very selective when it comes to numbers.

[electrodacus]

how about a system combined from PV doing electrolysis of a water down to oxygen and hydrogen during the day (sun presence) and for nights using a fuel cell? would this system be technically/economically possible for wide presence? Benefits are well known since Apollo programme - electricity, (hot) water and no pollution...

BR
Paul

I think I seen somewhere a similar solution but was for long therm energy storage as in they used PV energy is summer to generate and store hydrogen and then used that hydrogen to heat the house in winter.
It will maybe be a solution in places with very bad solar energy in winter months but not sure if even there this will be cost effective.
PV energy is so inexpensive now that even installing oversized PV arrays may be more economical than generating and storing large quantities of hydrogen.
For short/medium therm energy storage as in days up to a week nothing can beat thermal storage as far as I know.

Speaking of efficiency, I'd like to know how you PWM a battery off the same panels you power point the resistive heaters.  It seems you can be very selective when it comes to numbers.

The pdf paper in the first post explains how everything is done (project will be open source).
I do not use any PWM and what I do is redirect some of the panels to battery charging.
In my example I have the large 10kW PV array split in 6 smaller array's of different sizes and I'm able to redirect any of the sub arrays to battery charging.
There are a total of 39 panels and I can redirect to battery charging one up to all 39 panels depending on the amount of energy available and the combination of those 6 inputs will give me 39 individual levels basically I can connect any number of panels between 1 and 39
All panels that are not redirected to battery charging can be used for heating and storing that heat in thermal mass.
On the heating side there is also no PWM and there are again 6 outputs that can give me a theoretical max 63 levels of power (I will only use 31 levels in my example) so that I can get a Digital maximum power point tracking.
While the idea seems simple I'm not aware of any such system.
Hope you got the idea but if you read the document all is explained in more details and also all the benefit of this are explained also.

So there is no PWM done in the Digital MPPT or even in the Solar BMS.  PWM is not useful in any of this cases.

PS: In the PDF presentation there is actually even a link to a simple online simulator and a file that you load there with an extremely simplified version of the DMPPT with just 3 inputs and 3 outputs and playing with that can give a better understanding of how the DMPPT works.

[Kleinstein]

....
TEC are solid state so very reliable.
You can stack TEC modules to increase the temperature delta while maintaining high COP.
Yes cost will increase but you can get a TEC module now for $2 or $3 (that is what I paid a few years ago did not checked now).
And yes a compressor based heatpump can have a higher efficiency but as I mentioned I prefer the solid state reliability of TEC.
Based on the cost of raw materials TEC should be less expensive than compressor based so is maybe just about the production volume.
...

Stacking TEC modules does not increase the temperature difference and still maintain the COP.  This just does not work - it is against the laws of thermodynamics. In a simplified picture two elements in series will also need twice the electrical energy to drive and thus this would cut the COP to half for two elements in series and twice the temperature difference.  In the complete picture things get a little more complicated as the heat flow will not be exactly the same for both elements as the electrical energy is converted to heat too - so this give some minor corrections.

If things would be so easy to improve efficiency you would see much more stacked modules. In the low temperature difference limit, stacking of modules is not much more than making the legs longer and thus use a lower power density. So no change in COP if used with the same total temperature difference - just twice the costs for half the power. This is why you don't see stacked elements for low temperature differences.

The usual TEC elements use rather expensive materials, like alloys with bismuth and tellurium. Alternative materials (e.g. germanium based) are often even more expensive. So it is not all about small quantity, but also about the material used. This gets even worse if TEC would be used in larger quantities, as the tellurium reserves are very limited - thus significant more demand would cause prices to increase. Chances are those $3 modules were a special limited offer (excess inventory or even factory rejects). For higher power (e.g. kW range) - I am not sure a TEC based version would be cheaper than a compressor based solution. You can't compare just a bare TEC element to a complete heat pump system. The TEC system would also need quite some extra parts (e.g. heat exchanger / fan or pumps).

[electrodacus]

Stacking TEC modules does not increase the temperature difference and still maintain the COP.  This just does not work - it is against the laws of thermodynamics. In a simplified picture two elements in series will also need twice the electrical energy to drive and thus this would cut the COP to half for two elements in series and twice the temperature difference.  In the complete picture things get a little more complicated as the heat flow will not be exactly the same for both elements as the electrical energy is converted to heat too - so this give some minor corrections.

Have you read my examples above ? I know this discussion is getting out of hand but at least a few people reading this may clear some misconceptions.
How will the laws of thermodynamics be against this ?
Yes two elements in series will need twice the amount of power (actually slightly more if you want each stage to have the same COP for 10C delta) but then the equivalent COP of this two modules in series will be the same since they also extract more power from the cold side (twice as much if delta temperature is 2x higer).
So two stacked TEC modules will require slightly more than 2x more power but also move two times more so equivalent COP will be almost the same slightly smaller.

I think I mentioned before here and maybe this help's you understand better. If you have two peltier elements and you connect the cold side together on both (use some ideal thermal insulation around that cold side so they can not pump energy from the ambient) and supply both with same power say each with a COP of 3.25 for cooling of course 3.25 + 1 = 4.25 for heating  then the resulting COP of this system will be zero.
Yes zero in therms of cooling and 1 in terms of heating since all the heat you will get will be from the I2R losses so basically the supplied power.
 

If things would be so easy to improve efficiency you would see much more stacked modules. In the low temperature difference limit, stacking of modules is not much more than making the legs longer and thus use a lower power density. So no change in COP if used with the same total temperature difference - just twice the costs for half the power. This is why you don't see stacked elements for low temperature differences.

No you do not improve the COP by staking modules (COP not the same thing with efficiency) The COP is improved by using the peltier module with lower power and temperature delta since the problem with peltier is the thermal bridging since materials used between cold and hot side are relatively good thermal conductors so the lower the power the better the efficient as you probably seen in the last page of the spec http://www.thermonamic.com/TEC1-12706-English.PDF
 

The usual TEC elements use rather expensive materials, like alloys with bismuth and tellurium. Alternative materials (e.g. germanium based) are often even more expensive. So it is not all about small quantity, but also about the material used. This gets even worse if TEC would be used in larger quantities, as the tellurium reserves are very limited - thus significant more demand would cause prices to increase. Chances are those $3 modules were a special limited offer (excess inventory or even factory rejects). For higher power (e.g. kW range) - I am not sure a TEC based version would be cheaper than a compressor based solution. You can't compare just a bare TEC element to a complete heat pump system. The TEC system would also need quite some extra parts (e.g. heat exchanger / fan or pumps).

The small TEC1-12706 that is one of the most popular can be had even in low volume at $1.66 in China right now (just checked the price). Try a search on Aliexpress for this model TEC1-12706
And while if used at full rated power or close to say 12V is typical in most application it will require 5A for a delta of 40C and move just 23W while using 60W so COP of 0.38
While same module used at just 3V will require 1.23A at a delta of 10C so will move 12W wile requiring just 3.69W so a COP of  3.25
If I where to stack another module I will probably be using the TEC1-12707 with the cold side in contact with the hot side of the TEC1-12707 thus at the same 3V I will be able to move the necessary 12W + 3.69W = 15.69W at 10C delta while consuming about 4.8W 3Vx1.6A and maintaining the same COP 3.25
This two TEC seen as a single unit will be capable of moving a total of 27.69W from the cold side while using a total of 3.69W + 4.8W = 8.49W.

Some numbers are rounded and some data are aprox read from the graphs in the spec but the idea remains the same.

If you disagree please provide the calculation for this same example above.

[electrodacus]

Well this is embarrassing for me.

It seems I was wrong and I will try to explain how I setup the virtual experiment to explain the problem (to myself).

I consider ambient temperature +27C and have 3 barrels each containing 100liters of water each at different temperature one +27C same as ambient second at +17C and last one at +7C

First peltier say a TEC1-12706 will be in contact with the +7C barrel on the cold side and in contact with the +17C barrel on the hot side.
Since this powered at 3.69W and with a COP of 3.25 according to datasheet will extract 12W it means that the barrel will cool by 0.1C in one hour of operation (this was the reason I selected 100 liters so temperature will not change much so COP will be relatively constant).
The barrel on the hot side will heat up slightly more by 0.13C in the same hour since all of the energy from first barrel is transferred there 12Wh + the energy used by the peltier 3.69Wh
Now the third barrel that is at +27C is thermally connected with the hot side of the second peltier element and the cold side will be of course connected to the second barrel that is at +17C.
Considering the first +7C barrel thermally isolated so that it will lose 12W to ambient then second barrel ideal insulated no loss and third barrel not insulated at all so that it will mostly stay at +27C that happens to also be the ambient temperature.
Now is quite clear that while this will be running the first barrel will stay at +7C because it will be cooled at a rate of 12W while the loss to ambient will heat it back at a rate of 12W so temperature will remain constant.
The second barrel will also remain constant since the second peltier will extract the necessary 15.69W from the cold side while the 3 barrel will receive the 15.69W + the 4.8W so total 20.49W that will be transferred to ambient since the 3 barrel is not thermally insulated at all.
Now the COP for cooling will be just 12W / (3.69 + 4.8 ) = 1.41 while for heating COP will be 2.41

I think the best way is to add a remark in the original post so people ignore all the long discussion before.
Thanks to all involved for clarifying this for me. It seems I was the one that had a hard time understanding this.

Since this is now closed (I think unless I'm wrong again) you can ask question about my system DMPPT that has nothing to do with heat pumps.

[splin]

While same module used at just 3V will require 1.23A at a delta of 10C so will move 12W wile requiring just 3.69W so a COP of  3.25

Right. That first module will move 12W from the cold side with delta T of 10C and running at 1.23A:

If I where to stack another module I will probably be using the TEC1-12707 with the cold side in contact with the hot side of the TEC1-12707 thus at the same 3V I will be able to move the necessary 12W + 3.69W = 15.69W at 10C delta while consuming about 4.8W 3Vx1.6A and maintaining the same COP 3.25

Yes, fine so far...

This two TEC seen as a single unit will be capable of moving a total of 27.69W from the cold side

But that is where you keep going wrong. The total moved from the cold side (of the first module) is still 12W - after all it's still being driven at 1.23A and still has a delta T of 10C. It doesn't know that you just replaced its hot side heatsink with another peltier - how could it tell? There's nothing in the data sheet that says it will pump 12W @ 1.23A, 10C delta T *unless the hot side happens to be connected to another peltier instead of a heatsink*

If you want it start pumping 27.69 W from its cold side then you will have to more than double the current from the original 1.23A. And the 2nd module will also require a lot more power to move 27.69W instead of 15.69W. Anybody hear the sound of rapidly deflating COPs?

You have constantly ignored my statements that the second peltier is only moving the 12W provided by the first stage and not adding *another* 12W of heat pumping - it could only do that if they were in parallel, but then the total delta T would only be 10C. If the penny still hasn't dropped then please don't present yet another scenario without addressing the fundamental question as to why the heat pumped by the first stage would change due to the presence of another peltier on its hot side.

I gave you a link to a peltier manufacturer's technical data showing the equations for two and three stage coolers. They are quite straightforward  being mostly constants apart from the driving currents and the temperature differences. Please look at them where you can clearly see that the heat pumped from the first stage  is the same in the room and three stage cases. (Note that they number the stages starting from the hottest stage).

Finally, there is loads of information available on the net. All of which says that cascading peltier is useful if you want delta Ts higher than around 70C and that peltier are very inefficient for delta Ts above approx 20C. Do you really think that it never ocurred  to any of the experts, including the manufacturers, to simply run them somewhat below their full power and reap such rewards? After all, as you say they are dirt cheap compared to small compressors even if you have to use only 25% of their max capacity.

[splin]

Well this is embarrassing for me.

It seems I was wrong and I will try to explain how I setup the virtual experiment to explain the problem (to myself).

Ah okay.  Oddly the forum didn't warn me that your last response had been posted whilst mine was being prepared - it usually does.

Glad you've finally got it. 

[electrodacus]

Ah okay.  Oddly the forum didn't warn me that your last response had been posted whilst mine was being prepared - it usually does.

Glad you've finally got it. 

Thanks for insisting I was quite sure I was right
Luckily is cold enough here that I do not need cooling in summer so I was not thinking much about the problem.

I have a small fridge that was designed to be used in a car just 40 liter volume and uses one of those peltier probably the TEC1-12706.
There is nothing else other than the peltier element two heat sinks (one on each side) and two fans.
It was a bad idea since it will freeze everything inside with normal 20 to 28C ambient temperature while using about 50W
I reduced the voltage to 5V in winter and there it takes about 2A  10W including the fans that are inaudible and it manages to create a 17C delta between ambient and inside that is just right.
In summer when is a bit warmer inside I increase that voltage to about 6V and it uses about 13W (this also includes the DC-DC converter from 26V battery) and then delta is around 20C

In the past when I got a few peltier modules at 2 or $3 it was to experiment with them as generators and there they where about 3 to 4% efficient based on rough measurements.
Back then I was thinking on using thermal solar to heat a large thermal mass and then generate electricity as maybe a better combination than PV plus electrochemical battery.
Since then the PV panes drop substantially in price and the entire idea made no more economic sense.
Of course thermal mass storage is and will probably ever be one of the most economical ways to store energy.   

[Kleinstein]

Storing thermal energy is usually not that cheap, at least small scale. It can get efficient when used large scale, as the surface only scales like square while the mass scales with the third power. You not only need the thermal mass and insulation, but also heat exchangers to get the energy in and out - these can be problem when using a solid medium like rock. large containers also get difficult to transport - especially to remote areas. It also needs quite some space - so you might need extra protective structure.

One problem with storing heat for the winter is that this gives you not much more than one charge / discharge cycle per year. So it may be only 20-50 cycles over the life. Things get a little better for shorter time storage like day - night or maybe weekly for hot water. But still not that many cycles.

There are a few tries to store solar thermal energy for the winter - these usually need to be integrated when constructing the house and they are not really cheap, with storage being a large part of the costs, not the solar thermal collectors.

[CatalinaWOW]

Earth sinked heat pumps are the only successful application of long term heat storage that I know about. 

[electrodacus]

Storing thermal energy is usually not that cheap, at least small scale. It can get efficient when used large scale, as the surface only scales like square while the mass scales with the third power. You not only need the thermal mass and insulation, but also heat exchangers to get the energy in and out - these can be problem when using a solid medium like rock. large containers also get difficult to transport - especially to remote areas. It also needs quite some space - so you might need extra protective structure.

One problem with storing heat for the winter is that this gives you not much more than one charge / discharge cycle per year. So it may be only 20-50 cycles over the life. Things get a little better for shorter time storage like day - night or maybe weekly for hot water. But still not that many cycles.

There are a few tries to store solar thermal energy for the winter - these usually need to be integrated when constructing the house and they are not really cheap, with storage being a large part of the costs, not the solar thermal collectors.

I was not talking about long therm thermal storage just a few days to cover for solar energy availability. You can see a few example of thermal storage in my presentation.
In my particular case the house was designed with build in thermal storage at almost no additional cost since the thermal storage is also the structural part that was needed anyway and is comprise of a 14 cubic meter concrete floor/foundation.
Since is both thermal storage and radiator there is no need for any extra insulation since is inside the insulated house that needs heating and also no heat exchangers needed all is solid state.
Since the max temperature delta is limited at about 12C the storage capacity is 97.4kWh. The house heating needs are 1000kWh for the coldest month January here so a capacity of 97.4kWh should be good for max 3 days with zero energy from the sun. Of course zero energy from the sun is not realistic since even in the worst overcast days there is still significant amount received.
 
So yes I agree with you in regards to seasonal thermal storage and that is expensive but short therm solar energy storage to average the solar output so overnight and a few cloudy days is extremely cost effective.

Another example I used was an inexpensive plastic barrel with 206 liter capacity filed with water and an allowed temperature delta of 35C that will give a total storage capacity of 8.3kWh.  If this is inside the space that needs to be heated and the thermal loss to ambient is calculated so that almost no thermal insulation is needed then again no heat exchangers will be needed. Heating will be done the same way as the concrete floor with heating wires (basically just normal copper wires).
The cost of the barrel is 60USD new and water is basically free the heating wires needed are also inexpensive and cycle life is not an issue so you can imagine the comparison with a similar capacity 8.3kWh Lithium battery that has also a limited life and will probably need at least one replacement over a 25 to 30 year amortization period.

Earth sinked heat pumps are the only successful application of long term heat storage that I know about. 

See what I mentioned above and geothermal heat pumps are not cost effective for sure not cost effective at my location where just the geothermal loop will cost more than my entire solar PV heating instillation. 

[Kleinstein]

Thermal storage in the concrete structure will usually not allow for a 12 K temperature window - this would be rather uncomfortable in most cases. It might be OK with special insulation at the walls, but not with normal construction.  Just water barrels in the basement also need the room - so you have so take into account those costs. Usually one will also need some regulation, like fans of similar - other wise it is either way to warm or not giving much heat to the house. Without control of the heat flow, the useful temperature window would be more like 3-5 K, like a normal concrete structure.

It depends on the local climate - but even in really good areas there can be something like a week with snow cover or a few days without much sun. Similar really cold days / weeks might need twice the normal heat - so one needs a buffer for these days too. The combination of snow fall followed by a week of cold temperatures is not so rare. Worst case one can no rely on the snow to slide down by itself. So storage for 1 (or more) week at twice the normal power would be a good idea, if there is no backup solution. You won't need it every year, but one might.

At least here, on a overcast or foggy day, solar power is down to the 1% range - so hardy enough to start the PV.

[electrodacus]

Thermal storage in the concrete structure will usually not allow for a 12 K temperature window - this would be rather uncomfortable in most cases. It might be OK with special insulation at the walls, but not with normal construction.  Just water barrels in the basement also need the room - so you have so take into account those costs. Usually one will also need some regulation, like fans of similar - other wise it is either way to warm or not giving much heat to the house. Without control of the heat flow, the useful temperature window would be more like 3-5 K, like a normal concrete structure.

It depends on the local climate - but even in really good areas there can be something like a week with snow cover or a few days without much sun. Similar really cold days / weeks might need twice the normal heat - so one needs a buffer for these days too. The combination of snow fall followed by a week of cold temperatures is not so rare. Worst case one can no rely on the snow to slide down by itself. So storage for 1 (or more) week at twice the normal power would be a good idea, if there is no backup solution. You won't need it every year, but one might.

At least here, on a overcast or foggy day, solar power is down to the 1% range - so hardy enough to start the PV.

The example in the pdf presentation if for my particular case.
The house was designed and build by me and is in a fairly cold but sunny climate. Average temperature for the month of January (coldest month here) are -16.5C
This is the forth winter I spend in this house and currently for heating I use small propane tanks that are realy expensive and inconvenient.
Each propane tank contains 8kg of propane that has about 100kWh of stored energy and I use a small and inefficient propane heater that I run in average a few hours a day and that is outside and heats a glycol mixture in a closed circuit loop that then will transfer that trough a heat exchanger energy to an open loop made of a 206 liter barrel of water as a buffer and then circulated trough PEX tube trough my concrete floor.
The most propane tanks I used in a month was 11.5 two years ago when there was a colder winter and I'm at about 6.5 propane tanks so far this month.
If I'm sort of generous and say that the propane burner is 80% efficient that means I need 11.5 x 100kWh x 0.8 = 920kWh for the worst winter month in the past 4 years.
There are days when I can not heat at all due to high wind speeds and the fact that propane heater is outside and while it has now forced air for combustion is just a bad DIY job so it will still not work when wind speed is above 50 to 60km/h and that is fairly common here especially in winter.

The only thermal storage that I have know is that 14 cubic meter concrete floor that can go down to even 16C after 2 or 3 days without heating from a starting point of +21C and that is about as high as I can get now due to the fact that propane heater is limited at +70C since is designed for hot water for shower in camping (a realy cheap China made unit with 10kW max burner power).
Whit solar PV and heating cable I can get the concrete floor up to +28C if necessary and again if necessary it can drop down to a less comfortable +16C so that is where the +12C max range is coming from.
Of course this is a simplification since my house has quite a bit more thermal mass from the solid wood wall (unusual construction and if you realy want you can see the short video I made showing how the house is build )

So I know not just theoretical what the energy input for heating is for my house and also know the amount of solar. The snow here will not cover the panels since panels are at a steep 70 degree angle and is so cold that snow is not sticky. I may need to clean the panels maybe two or three times a year usually at the beginning or end of winter since then is when is warmer and snow may stick to the panels.
Of course each climate is different and so thermal mass and size of PV array will be quite dependent on that.
I guess you live in Germany where there is way less sun in winter but on the other hand the temperatures are not nearly as extreme as here so you need less energy to heat the same house. Also the cost of natural gas is probably significantly higher there than it is here so when you consider all this factors PV heating will still probably be the least expensive heating option even there.

I know most did not opened the pdf presentation and while the graph is present there I will also add it here.
Image is small just 175kb so I hope it will not affect those with slow internet connection.
The graph represent the daily energy generated by a 10kW PV array installed at my location and as you can see the worst case is about 8kWh in January and that worst case is just for a day most other semi cloudy days will be way better.
So in 95% of the cases thermal storage temperature delta will not change by more than 3 to 5C as you mentioned and in those worse days I can still use the available energy to heat the air so air stays at a more constant and comfortable temperature. I will have the heat recovery for house forced air ventilation ready by next winter and that should also save some energy compared with now opening windows each day. And the fresh air output from the heat recovery can be heated to desired temperature by a much smaller thermal mass storage for increased comfort.
 


Sorry for the long replay.

[ez24]

electrodacus

Why do you use the propane heater outside?  I used one of these for 3 winters inside and I am still alive ha ha   I just used common sense like no overnight, closed windows most of the time.  It sure helped and I lived in a concrete bunker.  Sure got tired of hauling 5 gal propane tanks.


https://www.amazon.com/Dura-Heat-Propane-TankTop-Heater/dp/B002LUSHPW/ref=sr_1_15?ie=UTF8&qid=1484868846&sr=8-15&keywords=propane+heater

[cmhansen]

Based on the cost of raw materials TEC should be less expensive than compressor based so is maybe just about the production volume.

The raw material cost for solar (panels?) is no more than the cost of drywall (per Tesla CEO), but being the same p and n doped silicon crystal you'll see why it's obviously not really anything to do with the cost of raw material and most definitely energy.  I also suspect energy embodiment is the same driver with Li batteries as[1] it takes only about 80g battery grade Li / kWh or about $2 worth and merely 2% the cost assuming $100 / kWh. In fact the highest cost I found current was 800k RMB/mt or only about $10 worth so at most 1/10 the cost of the fabled $100 point.

Thermoelectric tunneling might hold promise:
http://memim.com/thermotunnel-cooling.html
https://arxiv.org/ftp/arxiv/papers/0807/0807.2527.pdf

[1] http://benchmarkminerals.com/elon-musk-our-lithium-ion-batteries-should-be-called-nickel-graphite/
And cobalt is another to consider.  Lifepo4 is probably the most economical chemistry and great for stationary.  Specific energy is about half of other chemistries, but for autos the lower energy density makes it unfeasible mainly.

[electrodacus]

Why do you use the propane heater outside?  I used one of these for 3 winters inside and I am still alive ha ha   I just used common sense like no overnight, closed windows most of the time.  It sure helped and I lived in a concrete bunker.  Sure got tired of hauling 5 gal propane tanks.

Is not just about the carbon dioxide there will also be a lot of water vapor while burning propane and that is bad news when is also that cold outside. I do not remember the exact number but you get about 2x the amount of water by wight compared with the propane that you burn.  And since I burn about one of those propane tanks each 3 days all that water vapor will end up inside my house.
On top of that it will get way to hot inside the house and most of the heat will be stratified on the upper level of the rooms not to mention also a lot more will escape trough the windows since they will need to be opened all the time during heating.
The concrete floor will remain cold an uncomfortable while air will be to warm during the day and cold during the night when you do not use the burner.

[
The raw material cost for solar (panels?) is no more than the cost of drywall (per Tesla CEO), but being the same p and n doped silicon crystal you'll see why it's obviously not really anything to do with the cost of raw material and most definitely energy.  I also suspect energy embodiment is the same driver with Li batteries as it takes only about 80g battery grade Li / kWh or about $2 worth and merely 2% the cost assuming $100 / kWh. In fact the highest cost I found current was 800k RMB/mt or only about $10 worth so at most 1/10 the cost of the fabled $100 point.

Thermoelectric tunneling might hold promise:
http://memim.com/thermotunnel-cooling.html
https://arxiv.org/ftp/arxiv/papers/0807/0807.2527.pdf

Yes in may cases the cost of raw materials is realy low compared to the price of the final product .
Here is a recent paper that tries to give an idea about of the cost of PV panels http://www.nrel.gov/docs/fy16osti/65872.pdf
The paper is a bit detailed but fairly good and also when they talk about cost amortization they consider that for a grid tie connection so includes inverters and other equipment.
I think the future of energy will be solar and decentralized maybe some smart micro grid type stuff in densely populated areas.

Battery cost is similar but for low volume consumer prices as of now they are about $220/kWh capacity for LiCoO2 and similar high energy density cells all in the range of 500 to 1000 cycle life and LiFePO4 with an acquisition cost of $350 to $400 and 2000 to 6000 cycles so more suitable for stationary energy storage.
The fact that LiFePO4 is so expensive has to do with the low volume and demand for this since for now portable electronics and EV have a larger share than stationary energy storage.
Since 60 to 85% of a house energy use is in space heating and water heating the thermal storage can play a huge role and I do not think thermal storage will ever go away since nothing can realy compete with that in therms of cost.

[Kleinstein]

Heat storage in the foundation can lead to quite some extra heat loss - though mainly in phases when the heat buffer is relatively full and thus not that critical. Still a 12 K temperature window will include relatively low comfort temperatures. If would also be difficult to control the heat - so this should be only a part of the storage. Hot water storage also needs space inside or an extra protective structure and insulation - so it is not that cheap. It might be also a good idea to have some really hot water reserve for washing and similar.

Having a backup system (e.g. the propane gas from bottles) for really cold weeks can ease the buffer requirements a lot, even if you use it only very little. It can save you the storage you only need once a year or even less. It is a good idea to have some backup, just in case something brakes and you need the extra heat to survive.

For the rather low outside temperatures, forced ventilation with energy recovery could be a good way to reduce the energy need even further. They are usually needed to get really low heat requirements - at some point it gets more efficient than extra insulation.

With such a small house, it could be tricky to mound 70 m² at a steep angle. This could increase the installation costs. The 70m² might be enough for heating, but it might need mode for other needs.

[electrodacus]

Heat storage in the foundation can lead to quite some extra heat loss - though mainly in phases when the heat buffer is relatively full and thus not that critical. Still a 12 K temperature window will include relatively low comfort temperatures. If would also be difficult to control the heat - so this should be only a part of the storage. Hot water storage also needs space inside or an extra protective structure and insulation - so it is not that cheap. It might be also a good idea to have some really hot water reserve for washing and similar.

Not sure you seen my video on how the house was build. The foundation is a thermal insulated slab on grade. There is no thermal bridging to outside. You can also check the pdf version of the house project where you can see how the house is thermally insulated http://greensask.com/
You can see actually in this image below

Since house is so well insulated and there is large amount of thermal storage it can actually provide all the storage needs or worst case 80% of the storage needs.
I will have a much smaller thermal storage to preheat the air from the heat recovery unit.
I do not need large amount of thermal storage for hot water since there will use most of the water during the day and there will be enough energy even in overcast days to heat the water on demand.
The amount of water I use will also be realy low compared to typical usage.

Having a backup system (e.g. the propane gas from bottles) for really cold weeks can ease the buffer requirements a lot, even if you use it only very little. It can save you the storage you only need once a year or even less. It is a good idea to have some backup, just in case something brakes and you need the extra heat to survive.

I was considering a backup system since that way I could reduce the PV array size by about 30% but the thing is that the backups system that will be needed to provide just 10% of the heat while saving the 30% on PV array size will make the entire system more expensive and almost double the cost of heating.
The small propane tanks that I use now cost between 25 and $30 to refill and they contain 100kWh (8kg of propane) of energy and that is 25 to 30cent/kWh compared to energy from PV panels that is 2.4cent/kWh so an order of magnitude less.
Then when you replace 10% of the energy with one that costs 10x more the average price will double. And is way better to have a single system even if you need to double the size of the array and have huge excess of energy even in winter.
Natural gas is way less expensive than propane but that requires a connection that will cost way more than all the PV solar installation so it makes absolutely no sense. Price of natural gas also fluctuates a lot (2 to 3x) and you have no control over that cost.

For the rather low outside temperatures, forced ventilation with energy recovery could be a good way to reduce the energy need even further. They are usually needed to get really low heat requirements - at some point it gets more efficient than extra insulation.

Yes I expect to have some reduction is the energy needed when I install the heat recovery unit (rough theoretical calculation sees a 15 to 20% reduction compared to now). And yes you can not realy build an energy efficient house without including heat recovery unit.

With such a small house, it could be tricky to mound 70 m² at a steep angle. This could increase the installation costs. The 70m² might be enough for heating, but it might need mode for other needs.

I need about 64m² of panels and the mounting is no problem since it will be a ground mount. My house is on a 8 hectare lot so space is no issue.
If I had considered the PV heating when I designed the house I will have included the PV panels in to the house structure but then the house will needed to be something similar to an A frame type building so that panels are at least an a 60 degree angle so I get the most out of it in winter months and also help with the snow.
Here is a photo of my house when we got first snow this year. There are only 3kW of PV installed and I will need 9 to 10kW to provide 100% of the heating to my house
I will only have the panels on 2 row not three like it is not the case with the 9 x 260W panels so it is easier to install.

[Kleinstein]

Heating the hot water just when you need it, needs a high power. Years ago we had such a system for the summer - it was rated at something like 22 kW. So at best this would only work if the PV is really supplying 5 KW or so. So no more shower in the morning unless there is at least a small (e.g. 50 L) buffer - going a little larger might no be so much more expensive, and this would be high quality (controllable) storage - more replacing battery than just low temperature thermal storage in the building mass.

I know a backup system will add quite some costs, but it also saves quite a lot on the required storage and possibly a little on the PV. It could be the propane system you already have - the relatively high fuel costs are not that important if you only use it for may be 1-3 % on average. Still that could cut down the storage need by something like 3-5 days or maybe 30%-50%. The main part is to cut away those worst case bad weather phases that may happen every 5 years. Extra storage to the existing concrete can get rather expensive. You can't compare it to just PV, but more to PV+low cycle storage and it is the extra buffer that causes the costs. Even thermal storage gets expensive per kWh if used only once a year or less. I don't think the concrete floor is enough storage for those worst cases, even if you accept the room temperature to go down considerably (e.g. < 15 C) and thus get a little more out than normal.

[electrodacus]

Heating the hot water just when you need it, needs a high power. Years ago we had such a system for the summer - it was rated at something like 22 kW. So at best this would only work if the PV is really supplying 5 KW or so. So no more shower in the morning unless there is at least a small (e.g. 50 L) buffer - going a little larger might no be so much more expensive, and this would be high quality (controllable) storage - more replacing battery than just low temperature thermal storage in the building mass.

I know a backup system will add quite some costs, but it also saves quite a lot on the required storage and possibly a little on the PV. It could be the propane system you already have - the relatively high fuel costs are not that important if you only use it for may be 1-3 % on average. Still that could cut down the storage need by something like 3-5 days or maybe 30%-50%. The main part is to cut away those worst case bad weather phases that may happen every 5 years. Extra storage to the existing concrete can get rather expensive. You can't compare it to just PV, but more to PV+low cycle storage and it is the extra buffer that causes the costs. Even thermal storage gets expensive per kWh if used only once a year or less. I don't think the concrete floor is enough storage for those worst cases, even if you accept the room temperature to go down considerably (e.g. < 15 C) and thus get a little more out than normal.

Heating hot water on demand needs more power but I use small amounts of water so for me works. I'm also not a morning person so I will be up only after the sun will be up
Low flow shower heads can provide 4 to 6 liters per minute and in order to heat that water from say 20C room temperature to 40C that most people prefer requires a 20C delta.
Rising the temperature of 1 liter of water by 1 degree Celsius requires 1.16Wh of energy
Say you use 4 liter per minute for 10 minutes that is 40 liters so total energy needed is is 40 x 20 x 1.16 = 928Wh
Since that energy needs to be delivered in 10 minutes the heating power will need to be 928Wh x (60/10) = 5.5kW
The flow rate on my taps and shower is even lower than that at 1 to 2 liter/minute so in my particular case even less power is needed. (But is a particular case).

The added cost of the backup system will be much higher than over-sizing the solar system and thermal storage.
I prefer to spend two or three days each 5 years at a less comfortable internal temperature can even be 17C or 16C than have to deal with a backup system.
Thermal storage is extremely inexpensive. You can build a 160kWh thermal storage for around $2000

Just made a long video explaining how the DMPPT works and the example for my house if you get the time to watch this long video and deal with my bad English

[cmhansen]

electrodacus - 10% at 10x cost only increases cost by 90%, not 2x : )

$414 for 14kW mppt is surely good, and $240 for ~14kW mppt capacity is good too (trusting it's mppt):
http://www.ebay.com/itm/5-10-15-20-30A-PWM-Solar-Panel-Battery-Regulator-Charge-Controller-12-24V-DC-/171308053532?var=&hash=item27e2c1741c:m:mD5wQY2jD5vaJDldCLuXVzA

I do like your solution with thermal storage controller.  This can be implemented as a 'battery' to standard mppt system as a second battery bank (which is 'charged' once desired temp is reached).

[electrodacus]

electrodacus - 10% at 10x cost only increases cost by 90%, not 2x : )

Yes you are right that is way better

$414 for 14kW mppt is surely good, and $240 for ~14kW mppt capacity is good too (trusting it's mppt):
http://www.ebay.com/itm/5-10-15-20-30A-PWM-Solar-Panel-Battery-Regulator-Charge-Controller-12-24V-DC-/171308053532?var=&hash=item27e2c1741c:m:mD5wQY2jD5vaJDldCLuXVzA

 That is a PWM controller where do you see the mention of MPPT ? Ok just looked again and in description at one point they say MPPT solar charge controller of course it is not but they did not mentioned that in title where is clearly stated as a PWM only charger. So they will say it was just a copy and paste mistake in the description. But none will expect a 30A x 24V = 720W DC-DC converter for $12.
Of course there are plenty of fake MPPT lead acid charge controllers available on eBay.
In any case my Digital MPPT (the digital in front is extremely important ) since it is not a DC-DC converter is a completely different thing and nothing similar exists on the market.

I do like your solution with thermal storage controller.  This can be implemented as a 'battery' to standard mppt system as a second battery bank (which is 'charged' once desired temp is reached).

Not sure I get this last part. The thermal storage will be massive and will need many days of full sun (probably about a week) to get the thermal storage fully charged (it will almost never happen)
So the Lithium battery charging has priority then all the remaining energy is stored in thermal mass.
But since PV array is so massive to cover house heating the Lithium battery will be charged very fast and over 90% of the energy will still got to the much larger capacity thermal mass. 

[Kleinstein]

[quote author=electrodacus link=topic=81192.msg1118752#msg1118752
....
Not sure I get this last part. The thermal storage will be massive and will need many days of full sun (probably about a week) to get the thermal storage fully charged (it will almost never happen)
So the Lithium battery charging has priority then all the remaining energy is stored in thermal mass.
But since PV array is so massive to cover house heating the Lithium battery will be charged very fast and over 90% of the energy will still got to the much larger capacity thermal mass.
[/quote]

To have a system that will also work in winter and without often using a backup system, the PV capacity must be rather large. So even average winter power should be able to fully charge all the buffers rather fast (e.g. a week) - just a few sunny days would should fill the buffers. So the normal case would be battery and thermal buffer nearly full, and only depleting on a few dark days in a row. It is only a full buffer that really helps. Looking at just a few years data may not be enough to makes sure the buffers / PV capacity is sufficient, even for reasonable unfavorable weather.

With the concrete mass as a buffer there could be a problem with a lot of heat moving to the house one a not so cold day. So one might have to use extra ventilation to cool and thus has higher than normal losses on these days. It is not that bad, but is could effect the efficiency of the buffer. So the 12 C temperature spread looks rather high to me, unless there is some control over the heat release.

[electrodacus]

To have a system that will also work in winter and without often using a backup system, the PV capacity must be rather large. So even average winter power should be able to fully charge all the buffers rather fast (e.g. a week) - just a few sunny days would should fill the buffers. So the normal case would be battery and thermal buffer nearly full, and only depleting on a few dark days in a row. It is only a full buffer that really helps. Looking at just a few years data may not be enough to makes sure the buffers / PV capacity is sufficient, even for reasonable unfavorable weather.

With the concrete mass as a buffer there could be a problem with a lot of heat moving to the house one a not so cold day. So one might have to use extra ventilation to cool and thus has higher than normal losses on these days. It is not that bad, but is could effect the efficiency of the buffer. So the 12 C temperature spread looks rather high to me, unless there is some control over the heat release.

How fast the buffer will need to be charged to full depends a lot on location. In a location like mine where no more than 3 days without sun are expected the buffer can be much smaller than a location where one week without sun can be expected.
I do have also chances with 5 to 6 cloudy days but that is in November where average temperatures are much higher than in January so a full buffer in that climate will be able to cover a week the same way that the same buffer can cover 2 or 3 days in the much colder January.
As I mentioned before a fully discharged buffer for me is +16C and a fully charged buffer is +28C but the buffer will mostly work in the +19C to +25C or even smaller range most of the time.
The forced air ventilation can take care of keeping the air temperature inside at even more constant temperature.
In those few extreme cases when the buffer gets to say +16C the energy produced will be used to first preheat the air so that air temperature is maintained around +20C.
And on the other situation where buffer (concrete floor) gets above +25C (that will only happen manually if I expect realy bad whether for many consecutive days else it will be limited to +25C) and then the house air will not be preheated so that air temperature will be kept a bit lover.
The combination of floor temperature and house ventilation can keep the house air temperature in a narrow range of +20C to +23C at all times.
When is cloudy in January there is still energy being produced and not insignificant amounts and that energy is then used to charge a much smaller buffer that will control the air temperature.
 
If I take the concrete example based on that annual energy graph I have a good period where buffers will get full or close to and the starting with day 9 there is deficit of energy.
The house needs about 900kWh in January in an average year so that is about 30kWh/day to maintain the house temperature.
In day 9 say the concrete floor is at +25C and the concrete floor has a storage capacity of around 8kWh per degree Celsius.
So day 10 I get just around 22.5kWh from the sun that is a deficit of (7.5kWh) so say the concrete floor temperature by the end on day 10 drops by 1C so is now just +24C
Day 11 I get about 20.5kWh so concrete floor temperature will drop by about another degree Celsius and so it will be +23C
Day 12 I get around 42kWh of energy so that will cover the average 30kWh needed plus add another 12kW in thermal storage so temperature is now back again to around +24.5C
I can continue but you get the idea.
In November I only need about 400kWh to maintain the house warm since average temperature for that month is higher even if solar energy is worse with more much darker days than in January but then I only need about 14kWh/day to maintain the temperature so the thermal storage can deal with more consecutive bad days.
Another thing is that usually cloudy days are not as extreme cold as sunny days since the layer of clouds act as a blanket and keep the temperatures a bit higher.
In any case things are a bit more complex and all the interactions but I hope you get what I try to say.
 

[cmhansen]

Of course there are plenty of fake MPPT lead acid charge controllers available on eBay.
In any case my Digital MPPT (the digital in front is extremely important ) since it is not a DC-DC converter is a completely different thing and nothing similar exists on the market.

I had reservation it seemed dubious, however some are advertising PWM + MPPT, which is maybe a little more dubious.

Why are other MPPTs based on MCUs not 'digital'?  Can you safely assert all other MPPTs only use linear IC's?

With the concrete mass as a buffer there could be a problem with a lot of heat moving to the house one a not so cold day. So one might have to use extra ventilation to cool and thus has higher than normal losses on these days. It is not that bad, but is could effect the efficiency of the buffer. So the 12 C temperature spread looks rather high to me, unless there is some control over the heat release.

Good point.  I'm sure all have researched trombe wall, here is one report on efficiency:
http://www.nrel.gov/docs/fy04osti/36277.pdf

That claims nominal 13% efficiency for simple non-insulated design.

What about a fully insulated trombe wall 'structure'.  Three sides and bottom have insulation, and the south has double-pane glass with an insulated rolling curtain to cover at night.  The structure could even be detached from the house.  Use a blower to circulate heat only when needed, this is a small load to handle for the guarantee of never inducing unwanted cooling load and being able to control heat better.  Plus, the fact that the V in HVAC can be seen as a separate system and is still needed, required, even with radiant heating / cooling.  The trombe structure could last 'indefinitely' and has a lower upfront and amortized cost than PV too.  It could also be used as a preheater and slightly reduce PV need for hot water but pumping water may in fact come at a net loss with additional complexity for hot water needs... then again with such an 'oversized' trombe structure one may get enough hot water, being only a small fraction of the heat.  It should be good for adsorption chilling too, maybe 15kW or so heating capacity could give 2 ton ?? of cooling.  The majority of the south facing roof could be the trombe structure instead, or 'trombe roof', reserving a smaller space for PV.  And, no 'shading' issues with trombe structure for those around trees.

Dry soil has the same specific heat as sand (19% that of water), and ~90% that of concrete.  Wetting the soil (mud) will get you about 3x increase over dry.... one should be able to seal the moisture and even embed a soaker hose to easily 'recharge' if/when needed too.  I wonder if dirt could be used as the sorbent media for adsorption chilling, instead of silica gel.
http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html

[cmhansen]

Electrodacus - I can see how 'stepped shunting' the non battery reserve as heat is very attractive : )  That's exactly what you have implemented right?  I would argue MPPT only makes sense with dc-dc conversion, the effect is very similar, though it's confusing calling it MPPT.  More appropriately you could call it "MPPS" or maximum power point shunting.  There is what's called shunt MPPT to I am finding.

I had an idea once to concentrate PV and block / modulate maximum light so as to keep the cell operating at rated 1x power over a wide range of angles / shading / etc.... it is sort of like tracking but you can see how this could be better understood as shunting.

[electrodacus]

I had reservation it seemed dubious, however some are advertising PWM + MPPT, which is maybe a little more dubious.
Why are other MPPTs based on MCUs not 'digital'?  Can you safely assert all other MPPTs only use linear IC's?

Sorry you do not understand how the Digital MPPT works.
There are two parts to the DMPPT450
First one will take energy from a large PV array and using the so called Digital MPPT method delivered as heat to a set of 6 different value resistive elements.
The Load is made variable by combination of the 6 outputs so that Load can be varied in up to 63 distinct levels (number of combination with 6 ON/OFF outputs is 2^6 = 64 including all off).
By the fact that Load can be varied with this 63 distinct steps allows to maximize the power point for the PV array.
This sort of method only works for resistive type heating and is not applicable to battery charging.

Second part of the DMPPT450 has an output for the SBMS that will do battery charging so battery is also charged from this large PV heating array.
The heating array is split in 6 separate sub-arrays of different sizes and the DMPPT450 can select any number of this 6 separate PV array and redirect them to the output used for battery charging.
Since the total output of this large PV array is much higher than what the small Lithium battery can safely take the DMPPT450 will limit the output to battery at say 50A for a 200Ah battery and will select just a few panels to redirect to battery charging when is sunny and more panels when is less sunny up to all panels if is completely overcast and all panels put out no more than 50A.
So the PV panels redirection to battery charging uses a similar method to the Digital MPPT for the resistive load output.

All energy that is not needed for Lithium battery charging will go to thermal mass storage that has a much larger storage capacity than Lithium.
To better understand all the benefits of this check the long youtube video I posted explaining all this in more details.

What you know as a MPPT used in Lead Acid battery charging is composed of two parts one is usually software in a micro controller and second is the DC-DC converter that is controlled by that software.
The DMPPT450 has the software part (a bit different) but dose not need the expensive and unreliable DC-DC converter.
That DC-DC converter is expensive since it needs large inductors and electrolytic capacitors. Usually is a step don DC-DC converter that is controlled by the micro-controller in order to maximized the charge current to battery by finding the max power point. The current can be varied in a linear way (almost linear in any case with much better resolution) with the DC-DC converter.

A DC-DC converter that will be able to support a 14kW PV array as the DMPPT450 will be extremely heavy (expensive shipping) cost at least a few thousand dollar even for a less than good quality one and have huge internal losses thus probably need active cooling in order not to be even more heavy.
Say you get an excellent efficiency of 94% for the DC-DC converter that supports a 14kW PV array then the amount of heat generated inside the DC DC converter and that needs to be removed will be 14kW x 0.06 = 840W so it will be at full load a heater by itself
The DMPPT450 will have a total TDP of just around 50 to 60W at full load thus passive cooling is simple and the weight is maybe 20 to 50x lower so shipping cost is also significantly lower. Shipping alone from Canada for a heavy DC-DC converter can be more than the price of DMPPT450
The idea is that what you think when you say MPPT is extremely different from a Digital MPPT and while they both maximize the PV array output it is done in a completely different way with different HW and SW

Good point.  I'm sure all have researched trombe wall, here is one report on efficiency:
http://www.nrel.gov/docs/fy04osti/36277.pdf

That claims nominal 13% efficiency for simple non-insulated design.

What about a fully insulated trombe wall 'structure'.  Three sides and bottom have insulation, and the south has double-pane glass with an insulated rolling curtain to cover at night.  The structure could even be detached from the house.  Use a blower to circulate heat only when needed, this is a small load to handle for the guarantee of never inducing unwanted cooling load and being able to control heat better.  Plus, the fact that the V in HVAC can be seen as a separate system and is still needed, required, even with radiant heating / cooling.  The trombe structure could last 'indefinitely' and has a lower upfront and amortized cost than PV too.  It could also be used as a preheater and slightly reduce PV need for hot water but pumping water may in fact come at a net loss with additional complexity for hot water needs... then again with such an 'oversized' trombe structure one may get enough hot water, being only a small fraction of the heat.  It should be good for adsorption chilling too, maybe 15kW or so heating capacity could give 2 ton ?? of cooling.  The majority of the south facing roof could be the trombe structure instead, or 'trombe roof', reserving a smaller space for PV.  And, no 'shading' issues with trombe structure for those around trees.

That sot of thermal storage and solar heating hybrid has little to do with thermal storage that I'm talking about.
That thermal mass has little isolation from outside since is also used as a collector and is not that different than having large windows for direct solar gain.
Both of those methods are obsolete when compared with PV solar.

The problem is that in clod climate a lot of the energy gained during the day will escape during the night and in cloudy days and so that net gain of that system is extremely low sometimes even negative meaning that is better not to have that installed at all.
They conducted the test in a moderate location not as cold as mine else they will have negative results and that way they get just 13% efficiency but that is not to be confused with thermal storage efficiency and that is the amount of energy delivered by the sun say 5kWh per day per square meter in average that ended up contributing to house heating and in that case it will be 5kWh x  0.13 = 0.65kWh per square meter and day in average over the entire heating season.

A better performance can be achieved with the same surface made of PV panels (17% efficient) and a much smaller thermal mass (about 8x smaller) present inside the house not behind a simple glass with little air gap that has an incredibly low thermal insulation value.

Whit PV panels there is no loss during the night as it is with large windows used for solar gain or that method presented in that paper.

Dry soil has the same specific heat as sand (19% that of water), and ~90% that of concrete.  Wetting the soil (mud) will get you about 3x increase over dry.... one should be able to seal the moisture and even embed a soaker hose to easily 'recharge' if/when needed too.  I wonder if dirt could be used as the sorbent media for adsorption chilling, instead of silica gel.
http://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html

You can see different thermal storage options in my paper. Sand and concrete have about the same storage capacity and compared to water they have almost exactly half the storage capacity by volume.
Capacity by volume is usually important and water can have energy density similar to that of Lead Acid battery (as I mention at some point in my video).
If you want an even better energy density by volume than water then you can use the latent heat capacity of phase change materials with one of the popular ones being paraffin for low temperature storage application.
Absorption chillers can be used with almost any heat source including PV and DMPPT combination and while they are not particularly efficient COP of 0.7 to 1 they can be a solution since the energy source is extremely inexpensive with PV. I still prefer peltier even with COP of 1.4 at 20C delta. Luckily for need I do not need space cooling at my location just heating.       

Electrodacus - I can see how 'stepped shunting' the non battery reserve as heat is very attractive : )  That's exactly what you have implemented, it is very easy to understand with just those two words no?  I would argue MPPT only makes sense with dc-dc conversion, the effect is very similar, though it's confusing calling it MPPT.  More appropriately you could call it "MPPS" or maximum power point shunting.

See the answer above also.  Not sure stepped shunting is a better definition than Digital MPPT but I'm glad you got the idea and it was simple to understand.
What I do is Maximum Power Point Tracking is just that is in discrete steps 31 or 63 max steps so I call that Digital Max Power Point Tracking.
A DC-DC converter can be used even with a single resistive element to get the same effect but efficiency will be lower and cost much higher.
MPPT with DC-DC converter used in offgrid battery charging is a completely useless technology and obsolete. I made a youtube video about that just search for MPPT obsolete and it will be the first video.

[cmhansen]

Here's supposedly an upgraded CMTP02 I linked earlier:
https://www.aliexpress.com/item/High-tech-30A-12V-24V-Auto-Switch-MPPT-Solar-Panel-Battery-Regulator-Charge-Controller/32756101101.html

That listing is very explicit it is supposed to be a 'digital' MPPT and that indeed there is an older version very similar that is only PWM.  However for whatever reason MPPT is reported non-working:


I agree with a lot of what you are saying.  Still I'm reevaluating oversized solar-thermal + PV, PV alone will  [eventually?] be less expensive and reliable, I'll have to see again the price / watt you calculated for this.  Adsorbtion chilling can be done via resistive heating too and is a much better option than current TEC, I'd have to consider if AC is still better or not to that, you might as well shunt all the excess into usable cooling if adsorption units are more reliable and more economical.

[electrodacus]

Here's supposedly an upgraded CMTP02 I linked earlier:
https://www.aliexpress.com/item/High-tech-30A-12V-24V-Auto-Switch-MPPT-Solar-Panel-Battery-Regulator-Charge-Controller/32756101101.html

I agree with a lot of what you are saying.  Still I'm reevaluating oversized solar-thermal + PV, PV alone will  [eventually?] be less expensive and reliable, I'll have to see again the price / watt you calculated for this.  Adsorbtion chilling can be done via resistive heating too and is a much better option than current TEC, I'd have to consider if AC is still better or not to that, you might as well shunt all the excess into usable cooling if adsorption units are more reliable and more economical.

They of course do false advertising. They even show the PCB of that solar charger and is extremely clear that is a PWM only charger since there is no DC-DC converter in there.
Here is a photo of a proper 60A MPPT solar charge controller with 95% of what you see there being part of the DC-DC converter

The above image is from a clone of the popular Outback 60A MPPT charge controller and that costs about $500

Since PV array is normally that large to provide electricity and heating the cooling will not be a problem with almost any cooling option so absorption chilling low COP is not an issue when you have that amount of excess energy anyway.
I did not look almost at all at cooling since as mentioned before I do not need that. But my personal biased preference is for peltier Not even sure what is the cost and availability of absorption type chillers.
I know absorption chillers are used in RV industry since they can work with propane as the heat source.

[cmhansen]

I might research if dirt can be used for adsorption as adsorbent (seems unlikely):

Adsorption is a surface-based process while absorption involves the whole volume of the material

but maybe for absorption... more to learn.  I read silica gel lasts 30 yrs for adsorption, it can run as low as 60C, seems like water loop cooling is standard but surely ambient air exchanger would work too. 

Minisplits are really efficient but I read some reports of mold with humidity, maybe due to no antimicrobe filter like you find in central air.

Hmmm makes sense high-efficiency voltage conversion needs a 'storage' device being cap, coil or both.  Or, what about using / switching battery cells directly for this...  the more cells the finer grain switching can be and can 'adjust' the combined cell voltage to the array, e.g. charging a 370V battery if 100 cells were switched.... it's interesting to think about what you have in that light as you could say your DC-DC 'matcher' router/hub/switch 'converter' just moves the 'cap / inductor storage' off board.  I wonder if you are switching both panels and loads to make the right voltage matches.  The whole system makes a DC-DC converter.  A stand-alone converter between panels and loads is just a bottleneck. 

Why not grid tie too?  Good if it's CE and UL, in fact UL is required even for off-grid in the US as far as I know, some municipalities are banning off grid even.  I have a $.50/watt rebate available where I'm at.... net metering is nice that net is averaged per-month so battery and thermal storage is pretty much unnecessary, normal rate is about $.13 and excess sells back for $.02.  I think it's about $25 in base fees so ~1.25MWh excess is needed to truly get it to 0, but that isn't that feasible to do on 1/4 acre lot really.  I was allotted about 12.45kW capacity calculated from previous year all-electric use, at winter angle this gives me 1.35MWh / month winter average and those months I use ~3.1 or so, so 3 or 4 $220 bills plus $300 base I estimate $1200 / yr or so utilities minus water which isn't bad, ~1500sqft 'leaky' older home.

[Kleinstein]

Filling the thermal buffer all the way to full, only if wether report is calling for a longer no sun phase is not very reliable. This way the effective buffer capacity is reduced. Even if the next few days have not much excess energy predicted one would have to keep the buffer full as there might be a cold phase after that. So not filling up the buffer increases the risk of running out of heat, or one would need a larger buffer or PV. It is only if the predicted weather allows to fill up the buffer all the way later, that one could safely not put the energy in the buffer, without increased risk of running out of heat. With something like a 5 days reasonable reliable weather forecast this won't happen very often in winter.

Without much control over heat release it already is a problem, that a very hot buffer will send out quite a lot of heat and will thus initially loose its temperature faster than normally needed. So the upper temperature part is not that effective for storage. This might not be a problem if there is another thermal buffer that has much better control for the heat release, so initially one can use heat from the concrete only and use the more controllable buffer only later.

To get the heat out of the concrete buffer one would need it to be considerably warmer than the room. So using the energy from cooling to 16 C would only work if the room temperature really falls down, maybe to 12 C - maybe Ok for a few rooms, but not very comfortable. Even when using the floor for preheating fresh air, one would still need a second heat source to compensate the other heat loss. So I think the buffer capacity of the concrete floor is overestimated, especially at the lower temperature end. Without a heat pump (could be used for cooling too), temperature lower than room temperature (plus a little extra) has a low value. Possible use like air preheating or maybe water preheating would need extra investment.

I would more expect the concrete buffer part to be between 20 C and maybe 35 C (if the structure allows). The higher temperature part would have a small draw back: To compensate for to much heat released to the building one would need to cool be something like extra ventilation. So there would be extra heat loss if the buffer is near full, but still some extra heat could be stored for a short time, with little extra costs (ventilation for cooling).
It could be a good idea to have something like a thick carpet to slow down the heat release in a way that could be removed in a worst case period. By design the structure is only a short time storage, especially if not isolated against the room. Ideally coupling is variable - but this costs extra.

Anyway the concrete buffer should only be a part of the thermal buffer - maybe half, so you have at least some heat available you can control and keep for longer than maybe a 3-4 days.

[cmhansen]

To get the heat out of the concrete buffer one would need it to be considerably warmer than the room. So using the energy from cooling to 16 C would only work if the room temperature really falls down, maybe to 12 C - maybe Ok for a few rooms, but not very comfortable. Even when using the floor for preheating fresh air, one would still need a second heat source to compensate the other heat loss. So I think the buffer capacity of the concrete floor is overestimated, especially at the lower temperature end. Without a heat pump (could be used for cooling too), temperature lower than room temperature (plus a little extra) has a low value. Possible use like air preheating or maybe water preheating would need extra investment.

PV for heating is ideal ok.  Evacuated tubes fall linearly on efficiency if you look at the data (and heat flux formula):
http://www.heliodyne.com/wp-content/uploads/2016/03/Evacuated-Tube-Comp.pdf

https://en.wikipedia.org/wiki/Square-cube_law#Engineering_examples

This is the reason why underground molten salt storage can reach claimed 99% annual thermal efficiency once a large enough size is reached.  Volume is indeed important and it's actually advantageous to increase the heat buffer size in addition to using the highest specific heat possible (basically water), maximizing both minimizes both the temperature delta needed and also the percentage lost at the surface, of course insulation is still warranted. 

For a ~130m^2 home in cold climate I don't think even 20kW PV is enough heat buffer, one really should consider thermal collectors even assuming $.50/watt panels, also should be possible to use about half the area if it's 34% vs 17% efficient.  Those solar pool collectors / heaters show benefit:

http://www.houzz.com/photos/37108213/SunHeater-Universal-2-x-20-Solar-Heating-Panel-80-Sq-Ft-Set-of-2-traditional-heating-and-cooling

You get about 14.5m^2 for $194 shipped, at 20% efficiency that's almost 3kW!! or over 7x less installed cost assuming a 388W solar capacity for 194 ($.50/watt) shipped.  If they last 10* years, that's still over 2x less amortized cost.  True you'll need glycol and a pump so that adds to BOS.  If you have 30kW thermal, you've saved ~$13k up front and ~$7.5k over 30yrs.

Chances are that one won't last 10yrs. One could for even less make monolithic water panels from xypex waterproof concrete with lots of fiberglass to stop cracks.  Small enough concrete panels shouldn't crack and can be repaired. 

Water allows easy heat transfer in and out when needed.  If PV really is afforded for such a large cold climate heat buffer, place heating elements inside the water tank.  That should be more economical than a heated slab, you'll still have the inside watersource handler heatpump but you need, at least want, an airhandler anyways.  Circulate water to an insulated hole lined with a pool liner to make a tank (or use a tank).  Basically no loss at night.  Run the inside heatpump as needed. 

You couldn't tell by a single data point (i.e. device of only one size tested) or even the heat flux formula, but due to the 2/3 power law that applies to well everything physical, scaling anything becomes slightly non-linear.  This can add up, in a good way hopefully.

[electrodacus]

Filling the thermal buffer all the way to full, only if wether report is calling for a longer no sun phase is not very reliable. This way the effective buffer capacity is reduced. Even if the next few days have not much excess energy predicted one would have to keep the buffer full as there might be a cold phase after that. So not filling up the buffer increases the risk of running out of heat, or one would need a larger buffer or PV. It is only if the predicted weather allows to fill up the buffer all the way later, that one could safely not put the energy in the buffer, without increased risk of running out of heat. With something like a 5 days reasonable reliable weather forecast this won't happen very often in winter.

As mentioned before having the buffer at around 75 to 80% most of the time is OK and if weather forecast (that unfortunately is not always reliable) predicts multiple consecutive bad days then buffer can be charged to 90 even 100% even if less comfortable for that one or two days.

Without much control over heat release it already is a problem, that a very hot buffer will send out quite a lot of heat and will thus initially loose its temperature faster than normally needed. So the upper temperature part is not that effective for storage. This might not be a problem if there is another thermal buffer that has much better control for the heat release, so initially one can use heat from the concrete only and use the more controllable buffer only later.

To get the heat out of the concrete buffer one would need it to be considerably warmer than the room. So using the energy from cooling to 16 C would only work if the room temperature really falls down, maybe to 12 C - maybe Ok for a few rooms, but not very comfortable. Even when using the floor for preheating fresh air, one would still need a second heat source to compensate the other heat loss. So I think the buffer capacity of the concrete floor is overestimated, especially at the lower temperature end. Without a heat pump (could be used for cooling too), temperature lower than room temperature (plus a little extra) has a low value. Possible use like air preheating or maybe water preheating would need extra investment.

I understand now what you try to say. My house ambient air temperature is always the same as concrete floor temperature with no more than 0.5C difference between ambient air and concrete floor.
The amount of loss is extremely predictable and only based on delta between inside temperature and outside.
So if the concrete floor gets to 16C then ambient temperature is also at least 15.5C
So when I was mentioning absolute max range of 12C delta in the example I considered the +16C to +28C floor temperature range that will equate to a 15.5 to 27.5C ambient temperature unless you affect that by opening a window or something like that and after you close the window the ambient will stabilize again at around the floor temperature in no more than 1 to 2h
The wall that are 10cm solid wood and only thermally insulated on the outside additional mass that I did not added in the example to keep things simple but is not insignificant.
The wall is made out of about 8.5 cubic meter of wood that has a thermal heat capacity of about  0.35kWh per cubic meter per degree Celsius so almost additional 3kWh per degree Celsius additional to the concrete floor that has 8kWh per degree Celsius.
So while 12C delta for concrete floor may be a bit highs for comfort the storage capacity of the house is still probably at around 100kWh when also wood in the walls and Drywall are included at probably just 8C delta.
The example was just that showing how to calculate the thermal mass storage and the fact that a large floor can have significant amount of thermal storage at no additional cost since is part of the structure anyway and has the role of floor and foundation.   

I would more expect the concrete buffer part to be between 20 C and maybe 35 C (if the structure allows). The higher temperature part would have a small draw back: To compensate for to much heat released to the building one would need to cool be something like extra ventilation. So there would be extra heat loss if the buffer is near full, but still some extra heat could be stored for a short time, with little extra costs (ventilation for cooling).
It could be a good idea to have something like a thick carpet to slow down the heat release in a way that could be removed in a worst case period. By design the structure is only a short time storage, especially if not isolated against the room. Ideally coupling is variable - but this costs extra.

Anyway the concrete buffer should only be a part of the thermal buffer - maybe half, so you have at least some heat available you can control and keep for longer than maybe a 3-4 days.

As mentioned above there is no significant difference between concrete floor and actual indoor air temperature.
I just dislike carpets that is why plan was always for ceramic tiles and in floor heating.
I will say Concrete floor can easily be all the thermal storage needed even if you need to add more concrete than minimum required for structural integrity.
Yes a smaller 15 to 20% of the main thermal storage can make the ambient more constant for better comfort.

This is the reason why underground molten salt storage can reach claimed 99% annual thermal efficiency once a large enough size is reached.  Volume is indeed important and it's actually advantageous to increase the heat buffer size in addition to using the highest specific heat possible (basically water), maximizing both minimizes both the temperature delta needed and also the percentage lost at the surface, of course insulation is still warranted. 

For a ~130m^2 home in cold climate I don't think even 20kW PV is enough heat buffer, one really does need thermal collectors even assuming $.50/watt panels, also should be possible to use about half the area if it's 34% vs 17% efficient.

Water allows easy heat transfer in and out when needed.  If PV really is afforded for such a large cold climate heat buffer, place heating elements inside the water tank.  That should be more economical than a heated slab, you'll still have the inside watersource handler heatpump but you need, at least want, an airhandler anyways.  Circulate water to an insulated hole lined with a pool liner to make a tank (or use a tank).  Basically no loss at night.  Run the inside heatpump as needed. 

You couldn't tell by a single data point (i.e. device of only one size tested) or even the heat flux formula, but due to the 2/3 power law that applies to well everything physical, scaling anything becomes slightly non-linear.  This can add up, in a good way hopefully.

I do not doubt that you can create a large seasonal thermal storage with realy good efficiency outside the house but seasonal thermal storage makes no economical sense with inexpensive PV solar.

Maybe I already mentioned this in this forum and are sure present in my paper but here are the economical reasons.

This are just rough numbers based on 25 year amortization period.

PV panels  2.4 cent/kWh  (based on 80 cent/Watt acquisition cost, 25 years amortization and amount of solar energy at my location) it assumes you will be able to use all available energy and in my case I will be using only around 40 to 45% in average over a year.

LiFePO4 battery is a bit harder to calculate since it depends on model and how well it is used but a realistic number will be around 25cetn/kWh (a bit lower with DMPPT)

And last is thermal storage short therm few days estimated at 0.5cent/kWh

Best from an economic perspective is to maximize the thermal storage and PV array and reduce as much as possible the LiFePO4 storage.

Considering my example total cost for heating around $12k big part of that is the PV array at about 8k then much less thermal storage 2k and wires for heating and power transmission + DMPPT and some other accessories make up the rest.

Now thermal storage is say good for around 3 to 5 days and if you want seasonal storage then that will need to be able to store energy for 60 to 90 days and that means a thermal storage that is in a simplified way 15 to 30x more expensive and that means a cost of 30k to 50k for a seasonal thermal storage with savings of just 4k by reducing the PV array needed to half.
Of course that will not make sense for me in my climate and probably will also make no sense for anyone in any climate.
Even if you have horrible solar compared to my location adding extra PV capacity will still probably be a better option.

My house is 65m^2 and in a realy cold climate so a house that is build at same standards as mine ad same location that is 130m^2 will need probably just 16kW of PV since the larger the house the more efficient it is assuming the same level of thermal insulation.
As you seen in my comparison thermal collectors are actually more expensive than PV panels (just the panels) and when you consider the entire system that gap gets even larger so the only advantage is reduced collector area needed to half but at significant extra cost and complexity also reduced reliability to name just a few.

[Kleinstein]

With the thermal buffer so close coupled to the room temperature, it could rather fast get uncomfortable warm or cold. In this case even an 8 K or even 6 K temperature window is rather high and thus the storage capacity is getting rather small.
Adding more PV has only limited capability to compensate for too little storage. The worst case week can be rather bad, even if on average the conditions are good.

The solar condition for the OP are extremely good, so this only applies to the few good places with plenty of sun in winter. Here in Germany we are at something like half over the year and maybe 1/5 in winter.

[electrodacus]

With the thermal buffer so close coupled to the room temperature, it could rather fast get uncomfortable warm or cold. In this case even an 8 K or even 6 K temperature window is rather high and thus the storage capacity is getting rather small.
Adding more PV has only limited capability to compensate for too little storage. The worst case week can be rather bad, even if on average the conditions are good.

The solar condition for the OP are extremely good, so this only applies to the few good places with plenty of sun in winter. Here in Germany we are at something like half over the year and maybe 1/5 in winter.

I absolutely age with you that thermal storage and PV array size will need to be dimensioned for each particular case. I used my house and my location as an example and showed how thermal mass needs to be calculated.
Germany has fairly bad solar resource that is probably why people there where considering even seasonal thermal storage.
Still if space is not an issue then over-sizing the PV array is up to a point better than over-sizing the thermal storage and there is an optimum between the size of PV and thermal storage but that is realy specific to both location and house.

Yes a floor used as thermal storage is closely coupled to room temperature as long as there is no secondary system to control the ambient air. Since my concrete floor storage is marginal the plan is to add an additional thermal storage connected to heat recovery ventilation to have a better control of the air temperature thus maintaining a more constant room temperature.

If I stop all heating in the house the temperature drop in 24h will be between 1C and 2C depending on external temperature. The last 4 days where extremely cloudy here in January and I did no heating for the past 4 days.
The starting temperature was just +21C and I ended up now with just +16.5C after full 4 days without heating. This is an unusual year compared to average you seen from PVWatts and the outside temperature is also way above average for this period with an average of just around -5C over this last 4 days (actually it was warm even before that and will stay above until the end of the month at least). The average temperature for this month should be -16.5C and will probably not be the case this year. The beginning of the month was realy clod with maybe average around -20C but will still not compensate for this warm weather.
With current heating solution is difficult to heat the floor above 20 to 21C because the propane heater has a temperature limit and I use some small DC pumps and a heat exchanger plus a smaller 200 liter water buffer before sending water trough a PEX tube embedded in the concrete floor.
As it was a temporary solution I did not try to improve on the current system. I'm quite impressed by the fact that this cheap propane heater was able to last as long with this being the 4 winter and it seems it will probably make it.
The burner looked quite bad when I checked last year so a fail can happen at any time and then I will need a quick replacement.
You can see here the most recent photos of the temporary heating system https://plus.google.com/+DacianTodea/posts/VXbijJHXYmT  I know it looks bad but when I installed I was thinking it will be for one or two winters and now is almost 4 
This is an even older post https://plus.google.com/+DacianTodea/posts/SDVyfKjAGev and here you can actually see the burner https://plus.google.com/+DacianTodea/posts/8EKdxc3sD7j that was when it was newly installed so it looked good.
This is an inexpensive propane water heater for camping showers or stuff like that was not intended to heat a house

On one hand Germany has way less solar in winter than I have here but on the other hand the climate is much more moderate so a house of same size and level of thermal insulation will need much less energy to heat.
So for example Berlin in January will get just 228kWh with the same 10kW PV array where I get 1165kWh in same month
On the other hand Berlin average temperature in January is 0C where at my location is -16.5C thus almost twice as much energy is needed to keep the same house heated at 20C at my location than Berlin.
So my house if moved to Berlin will need a 25kW PV array and also probably about 2x the thermal storage capacity because of more consecutive cloudy days possible there.

Still if there is enough space for the larger PV array then it will still probably be the most cost effective heating option since I'm guessing here that natural gas will be more expensive than at my location.
If you use natural gas let me know what is the cost at your location for one unit of energy. If natural gas is 2 to 2.5x more expensive than here then solar PV will still be even there the most cost effective solution.

[Kleinstein]

The propane heater does not even look that bad. It might still work as a backup. Still it looks like there could be quite some heat loss to the outside. So the efficiency may not be that good and thus the need for heat is overestimated.

With an extra thermal buffer, the floor can be used as a limited thermal buffer. But there really should be a second one, where you have more control over the heat release. I would be surprised if there are not occasionally bad weather phases of something like a week or so. It is a relatively normal correlation that cloudy days will not be very cold and very cold days are often sunny. This helps a little, as one needs the buffer only for the not so could days. Still it looks like the floor is good for maybe 4 days and this with rather low temperature at the end.

Here in Germany it is not unusual to not see the sun for a month or even longer in winter. So it takes more than twice the buffer. There it also quite some variation from winter to winter. Average January temperature may be between about + 8 and -12 C. There is quite a lot of variation, because it depends on the weather pattern: sometimes the cold only comes til Poland and sometimes there is even snow in London. It depends on how large to cold high pressure region over Russia gets - so some years it's really cold and other years not. This makes even seasonal storage difficult, as one might need twice the normal heat in bad winters. So one has to be careful with just looking at averages.

[electrodacus]

The propane heater does not even look that bad. It might still work as a backup. Still it looks like there could be quite some heat loss to the outside. So the efficiency may not be that good and thus the need for heat is overestimated.

With an extra thermal buffer, the floor can be used as a limited thermal buffer. But there really should be a second one, where you have more control over the heat release. I would be surprised if there are not occasionally bad weather phases of something like a week or so. It is a relatively normal correlation that cloudy days will not be very cold and very cold days are often sunny. This helps a little, as one needs the buffer only for the not so could days. Still it looks like the floor is good for maybe 4 days and this with rather low temperature at the end.

Here in Germany it is not unusual to not see the sun for a month or even longer in winter. So it takes more than twice the buffer. There it also quite some variation from winter to winter. Average January temperature may be between about + 8 and -12 C. There is quite a lot of variation, because it depends on the weather pattern: sometimes the cold only comes til Poland and sometimes there is even snow in London. It depends on how large to cold high pressure region over Russia gets - so some years it's really cold and other years not. This makes even seasonal storage difficult, as one might need twice the normal heat in bad winters. So one has to be careful with just looking at averages.

The temperature of the flame is so high compared to glycol mix that absorbs that and with ambient that losses are not that high and not that dependent on ambient temperature. I also made rough measurements and base on that efficiency is not lower than 75 to 80%.
The burn rate is fixed and what I can do is just heat the water in the 206 liter barrel and then measure the water temperature increase over a specified period of time and calculate how much energy I get inside. Then I also can calculate how much time each propane take will last and the amount of energy it contains is known.
The thing is that the propane tank containing about 100kWh costs 25 to 30 CAD so that is about 10x more than the PV panels cost amortization if you are able to use all solar energy available.
Having an oversized PV array is still better than even covering just 10% of the energy with propane.
Yes an average year is just that and there are variations and I can see that this year compared to an average year.
Fore example than few consecutive cloudy days with very low solar output a few days ago look more like something you see here in November but the average temperature for those few days where also same as November and not January.
Right now as I write this there are +2C here and last night was a minimum of +1C and that is way above average in January here (-16.5C) and this is not a short period it started in the middle of January and will still last a few days so the second half of January this year looked more like a typical November in both temperature and solar output.

Yes I'm quite fortunate with the amount of sun here especially compared with Germany and other countries in Europe but solar will still be a good solution there since temperature is much milder and fossil fuel options cost 2x more there than here.
Average on each year for a month has little fluctuation no more than 10 to 15% more or less energy for a certain month in a different year.
For example at my location for January I had
2017  -14.3C (so far just 27 days)
2016  -11.2C
2015  -11.1C
2014  -15.2C
2013  -14.7C
2012  -10.0C
2011  -15.1C
2010  -13.3C
2009  -17.6C
2008  -15.0C
2007  -13.2C
2006   -6.4C
2005   -18.8C
2004   -18.0C
2003   -15.4C
2002  -13.0C
2001  -10.4C
2000  -15.6C

So I will say that using that average of -16.5C is good enough for design as the coldest year average was -18.8C in 2005 and there was that 2006 extra warm January with just -6.4C but not important.
So in your case I will design for a -8C average and all should be fine even in the coldest years that are probably also with more sun.
While a -8C average January seems like much different from a -12C when you look at energy needs the difference is much smaller since is based on delta between inside say +20C and outside so you have a delta of 28C to a delta of 32C so just about 14% more energy needed in the colder year than average.
The thing with solar PV is that it will produce energy even in those realy bad overcast day. And I noticed that having snow on the ground helps quite a bit when the panels are at a high tilt angle since the reflected light from snow can double the PV solar output . The fact that I had less than average solar those overcast days recently had also to do with the fact that all snow melted and everything was gray and dark no reflective surfaces around.

[CCitizenTO]

As for residential solar for heating, why not just heat your storage medium / working fluid directly? Why go through the electrical step? It will make substantially more efficient use of the sunlight. The technology for this has existed for a very long time.

I'm guessing he needs some electricity generation to run some appliances other than the furnace/heater/whatever (Fridge/Freezer/TV/etc...). That said I have seen solar powered hot water systems... It'd just be a matter of switching that into a radiator type system to heat the house. Would probably greatly improve the efficiency of the system too if the bulk of the energy is being used for heating as opposed to you know other stuff as well. With such a setup they may be able to get away with a smaller solar installation.

[Kleinstein]

Solar thermal collectors are possible too. They are mainly known for hot water, but can also be used to support room heating.

With the price for PV going down so far, PV plus heaters could be come an alternative.

The solarthermal collectors can be a little cheaper, but they require relatively expensive pipe-work and more maintenance for the liquid and pumps. Depending on the needed temperature the efficiency can be higher (maybe twice), but lower intensity light can not be used well for higher temperatures (e.g. 60 C). A large distance from the collector to the buffer also can be a problem.

As far as my estimate goes, it depends on the local conditions wether PV + heater or direct solar thermal is more cost effective. The lower costs for installation and maintenance compensates for more expensive collectors. It also depends on what is done DIY - some can do electrics, some can do pipes.

[electrodacus]

I'm guessing he needs some electricity generation to run some appliances other than the furnace/heater/whatever (Fridge/Freezer/TV/etc...). That said I have seen solar powered hot water systems... It'd just be a matter of switching that into a radiator type system to heat the house. Would probably greatly improve the efficiency of the system too if the bulk of the energy is being used for heating as opposed to you know other stuff as well. With such a setup they may be able to get away with a smaller solar installation.

Yes I need electricity also and the combination of the two makes the electricity part lower cost (that is an additional advantage).
But even if you only need heating solar thermal is more expensive and to get the exact numbers check the page 5  http://electrodacus.com/DMPPT450/dmppt-presentation-v01.pdf
The title is "Solar PV is now the most cost effective energy source" this means is also cheaper than thermal solar.
If thermal solar will have been a better option I will have selected that since cost was may main selection criteria for the house.

[Seekonk]

It is shocking when you see systems like http://www.sunbandit.us/ selling almost a conventional water heater in excess of $9,000 for the system. Just how does that pay off?  It is a conventional water heater with one extra heater for grid connect (3 total) a couple of panels and enphase converters.  I heat water with PV and the home made PWM converter to keep the panels at power point only costs about $25. Failing to keep the panels at power point will result in 50% power loss.  Your basic cost is almost just the panels.  If you design the system as supplemental heating and use only the lower heating element for PV, nearly 100% of the panels potential power generation is used 365 days a year. That surpasses almost anything else you can do with PV at a much lower hardware cost.  $500 for just two panels is a cheap way to get into solar.  Shamefully simple.  Just a nano,  a couple FET and some capacitors as the storage bank.

[electrodacus]

It is shocking when you see systems like http://www.sunbandit.us/ selling almost a conventional water heater in excess of $9,000 for the system. Just how does that pay off?  It is a conventional water heater with one extra heater for grid connect (3 total) a couple of panels and enphase converters.  I heat water with PV and the home made PWM converter to keep the panels at power point only costs about $25. Failing to keep the panels at power point will result in 50% power loss.  Your basic cost is almost just the panels.  If you design the system as supplemental heating and use only the lower heating element for PV, nearly 100% of the panels potential power generation is used 365 days a year. That surpasses almost anything else you can do with PV at a much lower hardware cost.  $500 for just two panels is a cheap way to get into solar.  Shamefully simple.  Just a nano,  a couple FET and some capacitors as the storage bank.

The name is quite clear "SunBandit"
Where do you see the price on that website ? I was not able to find a price. And what version of the Kit is that $9000 for ?
In any case they sell you a few components in the Kit.
I will suspect the most expensive part is the water heater tank.
Since they use microgrid inverters I do not even see the benefit since you need grid and you can just connect that directly to your house so any device can use that energy including the water heater.
I seen something in the past from Germany I think where they had an inverter but offgrid (no need for grid) but was also expensive.

The PWM thing works not sure what version is $25 but it can be relatively inexpensive for low power 500 to 1000W of PV panels that is more than sufficient for a normal hot water tank.
I seen one version of this PWM water heater on eBay for 250 USD and supports I think up to 3 to 4 panels in series about 750W to 1000W. Is that what are you referring and $25 was a typo ?

[Seekonk]

I would like to think this is a technical board and someone has the electronic nouse to build something simple.  Though, reading many posts I question that premise. "Just a nano,  a couple FET and some capacitors as the storage bank." refers to what you would have to buy for $25.  That $275 one has capacitors that can't handle the current and won't last long.  It also uses a IGBT, not a big issue if you want to fool around with getting rid of 10W of heat.   Everyone would like to have a tank like this http://www.akvaterm.fi/eng/Accumulators/Akva.38.html   Tank losses tend to be around 100-150W each hour.  Backup heating could be supplied by a low voltage transformer of only 250W.  A system is workable if you can get a 36V (50+V power point) string or higher and use a standard $10  2,000W 120V heater element.  Most electronic wall warts will operate at 50V giving an easy supply for micro.

On another board someone was quoted a complete install for $9,000 of the sunbandit.  This was a discounted price of normally $11,000 and they encouraged him to act quickly.

[electrodacus]

I would like to think this is a technical board and someone has the electronic nouse to build something simple.  Though, reading many posts I question that premise. "Just a nano,  a couple FET and some capacitors as the storage bank." refers to what you would have to buy for $25.  That $275 one has capacitors that can't handle the current and won't last long.  It also uses a IGBT, not a big issue if you want to fool around with getting rid of 10W of heat.   Everyone would like to have a tank like this http://www.akvaterm.fi/eng/Accumulators/Akva.38.html   Tank losses tend to be around 100-150W each hour.  Backup heating could be supplied by a low voltage transformer of only 250W.  A system is workable if you can get a 36V (50+V power point) string or higher and use a standard $10  2,000W 120V heater element.  Most electronic wall warts will operate at 50V giving an easy supply for micro.

On another board someone was quoted a complete install for $9,000 of the sunbandit.  This was a discounted price of normally $11,000 and they encouraged him to act quickly.

Sorry I somehow missed the fact that you mentioned a nano (as in AVR based mini arduino) and implied people will build their own version with parts worth about $25.
Is quite likely that those capacitors will not last much in that $275 PWM device.
I do not think that $25 is a realistic number if you want a quality electrolytic and mosfets and you will most likely need some other parts.
If you have a tank with 150W losses then you need 3.6kWh in 24h just to maintain the temperature and that is in average what 3 x 250W panels will be able to produce so they will be barely able to compensate for the losses.
 
A standard 2000W 120V heat element will have a resistance of around 7.2Ohm.
So with say two 60 cell PV panels (250W x 2) in series that have a max power point of around 60V you will get 60V/7.2Ohm = 8.33A so when sunny at noon you will have the FET fully on maybe and the rest of the time you will need to PWM to get closer to max power point but of course there will be losses on both FET and capacitor in this conditions (fairly significant).
With this fixed 2000W 120V fixed element nothing other than 2x250W will be able to work at max power point so you can not use 3 panels for example.
And with 500W you will get in an average sunny day around 2.4kWh/day so for a large water tank this will maybe just cover the losses of the tank.
This will quickly become expensive even if you can buy parts for $25 and you will assemble for free (for each 500W of PV) if you need 10kW of PV as I will need or 14kW the DMPPT450 supports to use for space heating.

[Seekonk]

Dacian, I think I deserve to use as crappy a numbers as you do.  I can buy 3 Canadian Solar 270W locally for $160 each. I said $500 in panels. That gives me 90V which is a good match.  I also said that this is supplemental  so that 100% of the panels output is always used, not heating 100% of all water with solar.  By doing this you get a cost performance better than with a heat pump.  Adding a heat pump to this would be ideal energy savings but it would never pay off the heat pump with reduced use.  I do heat water at my camp with just 900W of panels.  I can divert 2500WH a day since I have to run everything else at the camp, like refrigeration, with this same power. In that case I have two tanks and can switch between them and use both.  Take a course in reading comprehension. My numbers are real and a lot better than some of the ones you use.  In a world of jellybean designs where you can't tell a Hyundai from a Mercedes, I have an appreciation for something a little different.  I just wish you had someone to bounce some of your ideas off before you go into production.  They really aren't mature designs.  That said you ought to build one of these so you have something that is marketable.  Best of luck.

[electrodacus]

Dacian, I think I deserve to use as crappy a numbers as you do.  I can buy 3 Canadian Solar 270W locally for $160 each. I said $500 in panels. That gives me 90V which is a good match.  I also said that this is supplemental  so that 100% of the panels output is always used, not heating 100% of all water with solar.  By doing this you get a cost performance better than with a heat pump.  Adding a heat pump to this would be ideal energy savings but it would never pay off the heat pump with reduced use.  I do heat water at my camp with just 900W of panels.  I can divert 2500WH a day since I have to run everything else at the camp, like refrigeration, with this same power. In that case I have two tanks and can switch between them and use both.  Take a course in reading comprehension. My numbers are real and a lot better than some of the ones you use.  In a world of jellybean designs where you can't tell a Hyundai from a Mercedes, I have an appreciation for something a little different.  I just wish you had someone to bounce some of your ideas off before you go into production.  They really aren't mature designs.  That said you ought to build one of these so you have something that is marketable.  Best of luck.

Panels can be used with PWM for your system or with mine so panels will cost the same.  DMPPT450 is designed for a max 14kW PV array so not for small system to supplement domestic hot water.
If you where to need 14kW of PV panels using PWM method will be more costly and way more nasty (I'm referring to all that electromagnetic noise generated by switching 14KW)
If the DMPPT450 will have been just for heating the cost will have been 40% less than it is now so even less expensive but a large part of the DMPPT450 is related to battery charging also.

So say you just need 25$ for each 800W of panels then you need about 17 of this $25 devices to get to same 14kW capability of DMPPT450 and cost will them be $425 same as DMPPT but only have one function and done worse plus you need to build all those yourself is not already build.  Since DMPPT450 has no need for electrolytic capacitors it will most likely outlast those DIY $25 worth of parts devices be much smaller and much more efficient (way lower TDP).

On top of that DMPPT450 when used for both heating and Lithium battery charging together with SBMS will help reduce the battery capacity needed to at least half making savings of a few thousand $.

If you do not mind can you provide info about your setup. Like what panels are you using in that 900W array what capacitor and mosfet (TVS or other important parts). I can take a look at those and make a more clear analysis.

Also curios how you use the Battery (what type) and heating on the same 900W PV array?

[NiHaoMike]

LiFePO4 battery is a bit harder to calculate since it depends on model and how well it is used but a realistic number will be around 25cetn/kWh (a bit lower with DMPPT)

And last is thermal storage short therm few days estimated at 0.5cent/kWh

That really drives home why thermal storage makes the most sense for the three biggest loads in most homes - HVAC, refrigeration, and hot water. The remainder - mostly lighting and other electronics - is easily handled by a few kWh of batteries. Maybe only a few hundred Wh for a minimalist. Too bad lithium batteries and LED bulbs were really expensive back when I went to college, since the $40/month utility service charge in that area over the course of two semesters would easily buy nearly 2kWh of lithium batteries nowadays. (Multiply that by up to 4 years of college!) Take them on campus to charge, take them back home and have a pseudo off grid setup. (HVAC need is minimal to nonexistent over much of the school year, refrigeration could be done without as the grocery store was well within walking distance, and hot water is provided by the campus CHP setup.)

What I would really like to see more of are stationary bicycle generators. While limited to 100W or so, that's actually a lot for modern electronics. Make a portable version for charging portable electronics and we'll have a way to turn the obesity epidemic into a renewable energy source 50 times as energy dense as lithium batteries.

[electrodacus]

LiFePO4 battery is a bit harder to calculate since it depends on model and how well it is used but a realistic number will be around 25cetn/kWh (a bit lower with DMPPT)

And last is thermal storage short therm few days estimated at 0.5cent/kWh

That really drives home why thermal storage makes the most sense for the three biggest loads in most homes - HVAC, refrigeration, and hot water. The remainder - mostly lighting and other electronics - is easily handled by a few kWh of batteries. Maybe only a few hundred Wh for a minimalist. Too bad lithium batteries and LED bulbs were really expensive back when I went to college, since the $40/month utility service charge in that area over the course of two semesters would easily buy nearly 2kWh of lithium batteries nowadays. (Multiply that by up to 4 years of college!) Take them on campus to charge, take them back home and have a pseudo off grid setup. (HVAC need is minimal to nonexistent over much of the school year, refrigeration could be done without as the grocery store was well within walking distance, and hot water is provided by the campus CHP setup.)

What I would really like to see more of are stationary bicycle generators. While limited to 100W or so, that's actually a lot for modern electronics. Make a portable version for charging portable electronics and we'll have a way to turn the obesity epidemic into a renewable energy source 50 times as energy dense as lithium batteries.

Out of those mentioned hot water probably needs the most energy then HVAC and refrigeration not as much and can be reduced even more with better thermal insulation for the fridge.
Yes high energy density lithium cells can be had for about $220/kWh but those have lower cycle life 500 to 1000 cycles vs LiFePO4 that cost almost double at 350 to $400 but have a cycle life of 3000 to 6000 cycles.
So cost amortization is still better for LiFePO4 plus that is much safer in operation and also much safer for the environment.

Not sure if I mentioned here about the bicycle generator but I sure had discussions about this a few times.  I think that human generated power like a bicycle generators are a bad idea if energy is what you are after and not exercise.
Average human can not maintain more than 100W for long periods (hours) so what can be produced by even a fit human is extremely negligible probably similar to what a 30 to 40W PV panel that cost 30 to $40 and work for 25 years producing everyday as much as a fit human working hard to do that.  Of course the bicycle generator is also not free and most likely more expensive than a 40W PV panel.

[NiHaoMike]

With a heat pump water heater, the energy usage is quite small - on the order of a few hundred Wh per day. I actually built a heat pump water heater with a 1/2 ton compressor and that actually seems to be quite a bit bigger than necessary. There's little good reason to use a compressor smaller than that, since there's no real cost savings and the 300W or so it uses is a small load for any good sized off grid setup.

The main advantage of a stationary bicycle is that it would work when solar would not. Hence it would be a good complement to solar.

[electrodacus]

The main advantage of a stationary bicycle is that it would work when solar would not. Hence it would be a good complement to solar.

Solar actually works in all whether conditions.
A typical 250W panel will produce around 1.2 to 1.4kWh in a sunny day and at least around 0.1kWh in an overcast day so is never zero and most of the time much more than that minimum of 0.1kWh that only happens 5 to 8 days per year at my location. So a standard PV panel of that size 250 to 280W will produce in worst solar day as much as a human with one hour of pedaling and that panel will be 160 to $200 probably as much as a realy inexpensive bicycle generator. And 90% of the time that panel will produce an order of magnitude more than a single human on bicycle generator can do. People time is way to valuable for this even animals are way to valuable for this that is why you do not see a horse driven generator anywhere. Even if you do not care about the horse the food you will need to provide for him will cost more than the energy is worth.

[NiHaoMike]

I have in mind more of a backup in an off grid setup. Even if it's really just to ease the minds of those who are just starting to get into off grid, as an answer to "what if I run out of power and can't wait for the next day".

It is also worth noting that a 250W panel is definitely too big to be portable and even a 65W panel is bigger than what most people think of as portable. In contrast, there are already stationary bicycle generators that fold up into a very small package, intended for camping use. And then there are far more common crank chargers but most of those are designed cheap and don't actually work very well.

[HackedFridgeMagnet]

Wood can be cheaper if you live in a forest. And it warms you twice and keeps you fit.

https://grhgraph.wordpress.com/2010/02/11/chop-your-own-wood-and-it-will-warm-you-twice-henry-ford/

[electrodacus]

I have in mind more of a backup in an off grid setup. Even if it's really just to ease the minds of those who are just starting to get into off grid, as an answer to "what if I run out of power and can't wait for the next day".

It is also worth noting that a 250W panel is definitely too big to be portable and even a 65W panel is bigger than what most people think of as portable. In contrast, there are already stationary bicycle generators that fold up into a very small package, intended for camping use. And then there are far more common crank chargers but most of those are designed cheap and don't actually work very well.

There are portable PV panels that fold and are very light weight but of course they are at a premium in therms of cost because of the much lower production volume.
You can not just run out of power since you have SOC indicators so you know exactly how much energy you have stored and will know ho to use.
I live offgrid for about 4 years now with solar only and no other backup.

[electrodacus]

Wood can be cheaper if you live in a forest. And it warms you twice and keeps you fit.

https://grhgraph.wordpress.com/2010/02/11/chop-your-own-wood-and-it-will-warm-you-twice-henry-ford/

Even if you live in a forest and can get the wood for free the cost of heating will still be higher. You need to consider the burner that has a cost and limited life and if to that you add your time then cost is considerably higher than solar PV.
You will be fit in summer when you collect the wood for a few weeks but the air quality if you have the stove inside the house will more than negate the benefits

[HackedFridgeMagnet]

The air quality of our house is fine, its a fairly modern wood burning stove. Though bringing dirty logs into the house makes a bit of a mess.
We would have to burn the wood anyway as it's an on going bush fire threat.
But I agree solar energy would be far easier and much better for most.

[CatalinaWOW]

Where I am I would have to do nearly as much wood cutting to keep solar working as I would keeping a wood stove going.  Those pesky trees keep growing and generating more and more shade. 

Of course I could build a structure taller than local tree growth and then have really good insolation.  But I haven't found an economical way to make a large area structure that is 20 meters tall and can take the large wind loads associated with large solar arrays.  And like HackedFridgeMagnet I would still end up clearing trees for a variety of reasons including managing fire hazard.

There is no one answer to renewable energy.  It is very site specific.  Sometimes the answer is hydro.  Sometimes solar.  Sometimes wind, though I pity those who live places where wind is a viable stand alone energy source. 

[mtdoc]

I'm a big fan of solar PV. I have my own 4500 watts of PV installed and plan to install more.  BUT - it's just not realistic for most people who live in cold climates with large amounts of rain/snow in the winter to rely solely on PV for all of their heating needs - no matter how inexpensive PV panels have become, how well insulated their home is, how much heat storage/buffer they have,  etc.  There may be a few cold weather climates where there is enough winter sun to make it work provided it's a small, very well insulated home - but those locations are few in number.

All of the people I know who live off grid with PV have some supplementary energy source for heat - either wood stove, wood masonry heater or propane.  Modern wood stoves or masonry heaters are very efficient and do not have any significant impact on indoor air quality. Outdoor air quality can be affected if there is a large density of these in a small area subject to atmospheric inversion conditions but that is not the case in off grid locations.

I also know of no one who lives off grid with PV who does not have some backup source of electricity generation - usually a generator or if they're lucky wind or micro hydro.

[electrodacus]

The air quality of our house is fine, its a fairly modern wood burning stove. Though bringing dirty logs into the house makes a bit of a mess.
We would have to burn the wood anyway as it's an on going bush fire threat.
But I agree solar energy would be far easier and much better for most.

I did considered wood or pellet for my heating but for me is significantly more expensive than solar and on top of that requires much more work. Pelets are cleaner and even cost less here if you want to by the wood but the feeding mechanism is not always great and all that installation is expensive and not that reliable.

[electrodacus]

Where I am I would have to do nearly as much wood cutting to keep solar working as I would keeping a wood stove going.  Those pesky trees keep growing and generating more and more shade. 

Of course I could build a structure taller than local tree growth and then have really good insolation.  But I haven't found an economical way to make a large area structure that is 20 meters tall and can take the large wind loads associated with large solar arrays.  And like HackedFridgeMagnet I would still end up clearing trees for a variety of reasons including managing fire hazard.

There is no one answer to renewable energy.  It is very site specific.  Sometimes the answer is hydro.  Sometimes solar.  Sometimes wind, though I pity those who live places where wind is a viable stand alone energy source.

Yes if you are in a forest is a bit of a problem to find a good spot for solar PV array. If I knew about the cost drop in price of solar PV panels when I designed my house I will have build a sort of A frame house where the south face will have been covered in PV panels and that will have been enough to fully heat the house.
I will have saved some money on cables since now I need the array on the ground somewhere in front of the house.
Not many people have access to hydro but that is of course a good option in those particular case. Wind is not a good option. I have good wind resources here and I considered all sorts of wind turbines (even had a small one for a year) and the large inconsistency in wind availability requires larger storage so more cost and the tower for that small 300W wind turbine was more expensive than the turbine plus the cable needs to be thinker and longer than for a similar PV panel.
There are just to many downsides to wind for small scale not sure how things look at large scale.

[electrodacus]

I'm a big fan of solar PV. I have my own 4500 watts of PV installed and plan to install more.  BUT - it's just not realistic for most people who live in cold climates with large amounts of rain/snow in the winter to rely solely on PV for all of their heating needs - no matter how inexpensive PV panels have become, how well insulated their home is, how much heat storage/buffer they have,  etc.  There may be a few cold weather climates where there is enough winter sun to make it work provided it's a small, very well insulated home - but those locations are few in number.

All of the people I know who live off grid with PV have some supplementary energy source for heat - either wood stove, wood masonry heater or propane.  Modern wood stoves or masonry heaters are very efficient and do not have any significant impact on indoor air quality. Outdoor air quality can be affected if there is a large density of these in a small area subject to atmospheric inversion conditions but that is not the case in off grid locations.

I also know of no one who lives off grid with PV who does not have some backup source of electricity generation - usually a generator or if they're lucky wind or micro hydro.

I live in a cold climate since I'm in Saskatchewan Canada so colder than any state in US. Also almost all states in US will have better solar than I have here so if it works for me it will likely work anywhere in US.
I know 99% of people do not use solar PV for 100% of the energy that is why is hard to believe is not only possible but is in most cases the most cost effective method.
The example in the pdf document is for my house at my location and my small 65m2 (~700sqft) can be powered 100% with just a 10kW PV array
And yes a typical house in North America is 3x larger and 3x less well insulated so requires up to 9x more energy if it where in the same climate as mine but that is only important for the area needed for the PV array since cost per unit of energy will still be better for solar PV than wood or propane.
I live for about 4 years here offgrid with solar and I do not have any backup for the electricity part. Heating is still temporary with propane (extremely expensive) but by next winter I hope it will be 100% with solar PV.

[mtdoc]

I live in a cold climate since I'm in Saskatchewan Canada so colder than any state in US. Also almost all states in US will have better solar than I have here so if it works for me it will likely work anywhere in US.

Well, I don't know where you are in Saskatchewan I see now that you're from Regina which is far Southern Saskatechewan. There are several places in the  lower 48  US that have lower average annual temperatures than southern Saskatchewan and some with lower annual temps than central Saskatchewan.  Then of course there is Alaska ...

As far as sunshine goes, there are many, many places in the lower 48 US states with much less sunshine than Saskatchewan.

Just for example, Minnesota (one of the coldest US States) averages 180-200 days with sun  per year compared to Saskatchewan's 300 - 325 days (Regina is 322).

Western Washington state where I live and where the large population centers are , averages only 130 -160 day with sun per year.

And then there's Alaska...

Saskatchewan is  a very sunny place - lucky you.

All the weather data for Canada and the US to back up these facts can be found HERE

I agree with your general premise that cheap PV prices mean that solar PV is very cost effective and can and should be more than it is but your are overselling it, with exaggeration.

[electrodacus]

I live in a cold climate since I'm in Saskatchewan Canada so colder than any state in US. Also almost all states in US will have better solar than I have here so if it works for me it will likely work anywhere in US.

Well, I don't know where you are in Saskatchewan I see now that you're from Regina which is far Southern Saskatechewan. There are several places in the  lower 48  US that have lower average annual temperatures than southern Saskatchewan and some with lower annual temps than central Saskatchewan.  Then of course there is Alaska ...

As far as sunshine goes, there are many, many places in the lower 48 US states with much less sunshine than Saskatchewan.

Just for example, Minnesota (one of the coldest US States) averages 180-200 days with sun  per year compared to Saskatchewan's 300 - 325 days (Regina is 322).

Western Washington state where I live and where the large population centers are , averages only 130 -160 day with sun per year.

And then there's Alaska...

Saskatchewan is  a very sunny place - lucky you.

All the weather data for Canada and the US to back up these facts can be found HERE

I agree with your general premise that cheap PV prices mean that solar PV is very cost effective and can and should be more than it is but your are overselling it, with exaggeration.

Yes I wanted to mention that Alaska is excluded but I was thinking that was obvious so did not mention.

But Minnesota is in a better place from solar and climate point of view than Saskatchewan.
Go here http://pvwatts.nrel.gov/ select Minneapolis use a 10kW PV array at 60 degree tilt and leave all other values at default you will see an annual production of 13297kWh vs 14760kWh for Regina Saskatchewan vs 10309kWh in Seattle
Then look in to details for the worst winter months where you have
Minnesota
824kWh in December
1117kWh in January
1146kWh in February

Regina
897kWh in December
1166kWh in January
1252kWh in February

Seattle WA
338kWh in December
415kWh in January
538kWh in February


Now look at the average temperatures for this two locations for the same winter months

Minnesota https://en.climate-data.org/location/1522/
-7.5C in December
-10.9C in January
-7.4C in February

Regina  https://en.climate-data.org/location/373/
-13.3C in December
-16.7C in January
-13.1C in February

Seattle WA  https://en.climate-data.org/location/593/
+5.1C in December
+4.3C in January
+6.1C in February

So yes if I move my house around Minneapolis or Seattle it will do better than here around Regina Saskatchewan because on the winter temperatures vs amount of solar energy.

If I want to heat the house in Regina Sask at +20C in January I need to put enough energy to maintain a 20C + 16.7C = 36.7C delta where in Seattle you need 20C - 4.3C = 15.7C delta
36.7C / 15.7C = 2.34 less energy to heat the same house at this two different locations.

So yes excluding Alaska US has similar or better conditions than I have in Regina Sask. I can move my house and can heat and power my house with a 10kW PV array in any US state except Alaska.

[mtdoc]

You're cherry picking your locations and months and even then the numbers you post do not fully support your assertions. (Seattle's solar insolation is less than half of yours).

You're the one who stated that your location was colder than any place in the US which is not true - even if you exclude Alaska.  Just for example, from the website you link, Angle Inlet, Minnesota is colder. (Dec -14 C, Jan -18.1 C, Feb -14.5 C).

You're the one who said almost all states have better solar resource than you.  Depending on what you mean by "almost all" that is also not true.

My only point is that you live in a cold but relatively sunny location in a small, very well insulated home and therefore your attempt to provide for all your energy needs with solar PV is not going to be replicable for many people living off grid in the USA.  Yes, or course for many others it will. You're just overselling your assertion is all. 

As I've said, I am a big fan of solar PV and it has become a very cost effective energy source - even the most cost effective in some locations. It's not the complete energy solution for everyone (or maybe even most) who lives off grid though.

[CatalinaWOW]

Where I am I would have to do nearly as much wood cutting to keep solar working as I would keeping a wood stove going.  Those pesky trees keep growing and generating more and more shade. 

Of course I could build a structure taller than local tree growth and then have really good insolation.  But I haven't found an economical way to make a large area structure that is 20 meters tall and can take the large wind loads associated with large solar arrays.  And like HackedFridgeMagnet I would still end up clearing trees for a variety of reasons including managing fire hazard.

There is no one answer to renewable energy.  It is very site specific.  Sometimes the answer is hydro.  Sometimes solar.  Sometimes wind, though I pity those who live places where wind is a viable stand alone energy source.

Yes if you are in a forest is a bit of a problem to find a good spot for solar PV array. If I knew about the cost drop in price of solar PV panels when I designed my house I will have build a sort of A frame house where the south face will have been covered in PV panels and that will have been enough to fully heat the house.
I will have saved some money on cables since now I need the array on the ground somewhere in front of the house.
Not many people have access to hydro but that is of course a good option in those particular case. Wind is not a good option. I have good wind resources here and I considered all sorts of wind turbines (even had a small one for a year) and the large inconsistency in wind availability requires larger storage so more cost and the tower for that small 300W wind turbine was more expensive than the turbine plus the cable needs to be thinker and longer than for a similar PV panel.
There are just to many downsides to wind for small scale not sure how things look at large scale.

You are right.  Wind is rarely the answer as a sole energy source.  But there are places where for all practical purposes the wind blows all the time.  Much more than even windy places like Regina.  Not pleasant places to live at all and generally cloudy also, but if you have to live there wind might work out.

Solar has potential in lots of places.  But even with solar there are limitations.  In my current case I didn't mention the bottom of a valley location, or the poor orientation of the roofs (driven at least partly by local geometry) of the already existing house.  Yes, if you are buying land and building a house intended for solar you can select for these factors, but economics works here also.  Prices for land best suited for solar in a given area will rise.  Often for reasons unrelated to solar.  Hilltop locations which have the most access to solar also tend to be prized view lots in urban areas.

[electrodacus]

You're cherry picking your locations and months and even then the numbers you post do not fully support your assertions. (Seattle's solar insolation is less than half of yours).

You're the one who stated that your location was colder than any place in the US which is not true - even if you exclude Alaska.  Just for example, from the website you link, Angle Inlet, Minnesota is colder. (Dec -14 C, Jan -18.1 C, Feb -14.5 C).

You're the one who said almost all states have better solar resource than you.  Depending on what you mean by "almost all" that is also not true.

My only point is that you live in a cold but relatively sunny location in a small, very well insulated home and therefore your attempt to provide for all your energy needs with solar PV is not going to be replicable for many people living off grid in the USA.  Yes, or course for many others it will. You're just overselling your assertion is all. 

As I've said, I am a big fan of solar PV and it has become a very cost effective energy source - even the most cost effective in some locations. It's not the complete energy solution for everyone (or maybe even most) who lives off grid though.

I did not try to cherry pick a location just took the largest known city in the state you mentioned.
I see that the particular town with a population of 60 people according to google has slightly lower temperatures than my location (not significant) and will require 2 to 3% more energy to heat than at my location.
If you look on the map where that small town is located is basically in Canada and it also has lower solar resources but I can call this cherry picking

I guess most people living offgrid have enough land for a large ground mount PV array. All other energy sources will be way more expensive when you take the entire system in to account.
If you live in a house that already has a natural gas connection and the natural gas furnace then there will be no gain to go with solar PV.
But If you have an offgrid house and you use propane, heating oil or wood/pellets then I will say is extremely likely that PV will be significantly more cost effective especially in cold locations where heating season is a big part of the year.
And this is just the benefit for heating used stand alone but when electricity is also needed the combination of heating and electricity brings even more advantages since it reduces the battery size needed for electricity storage by at least half if not more and makes the offgrid electricity competitive with grid if not better.

The 10kW PV array as mentioned before will produce 14.7MWh in a year at my location and from that I will use around 4000 to 5000kWh for heating depending on winter and in my case just around 1000 to 1200kWh electricity (maybe that will increase in the future but is not relevant there is plenty of excess).
Total cost of the parts including the battery SBMS and inverter that I already have will be around $15k
Assuming a 25 years amortization period where another 1000 to $2000 battery may be needed in the future and a $400 inverter say $17k for 25 years
$17k / 25 years = $680/year = $56.6/month
The PV array that is the main cost of the system will continue to work probably for much more than 25 years so cost amortization will be even lower.
Selecting any other heating option like wood or propane will make the electricity part much more expensive close to 2x the cost mostly because of the higher battery capacity needed.
So while you can split that $57/month in say about $40/month for heating and $17 for electricity the electricity will get to around 30 to $35/month without the oversized PV array used for heating and with the large capacity battery so then your separate heating solution will need to be just $22/month about $264/year in order to be equal with PV heating.

Hope you get the idea related to benefit of combining heating and electricity.
I just do not see any way for any other energy source to compete with PV and PV and Lithium battery prices will only go down while other energy sources will probably stay the same or even go up in price.
And yes there is that disadvantage that you need to pay in advance for all that energy by purchasing the PV panels.

You are right.  Wind is rarely the answer as a sole energy source.  But there are places where for all practical purposes the wind blows all the time.  Much more than even windy places like Regina.  Not pleasant places to live at all and generally cloudy also, but if you have to live there wind might work out.

Solar has potential in lots of places.  But even with solar there are limitations.  In my current case I didn't mention the bottom of a valley location, or the poor orientation of the roofs (driven at least partly by local geometry) of the already existing house.  Yes, if you are buying land and building a house intended for solar you can select for these factors, but economics works here also.  Prices for land best suited for solar in a given area will rise.  Often for reasons unrelated to solar.  Hilltop locations which have the most access to solar also tend to be prized view lots in urban areas.

Yes there may be a few places where wind is more constant and maybe good to consider. I'm a bit biased here since I always prefer solid state devices and dislike any moving parts.
Is unfortunate that you have bad access to solar but from what you say that seems a as a grid connected house and live in some sort of urban area. There is always the possibility to move to a location with better solar access
Most house in urban areas are large and not properly insulated (just minimum by local code) so the surface of the PV array needed to provide 100% of the energy will be high and most likely the space for that will not exist (small lots in urban area).
While solar PV is cheapest it will not work in any place because of this limitations mentioned and probably others.
There is no doubt in my mind that solar PV will probably be the dominant energy source in 10 to 15 years and many things will change with this.

[mtdoc]

I see that the particular town with a population of 60 people according to google has slightly lower temperatures than my location (not significant) and will require 2 to 3% more energy to heat than at my location.
If you look on the map where that small town is located is basically in Canada and it also has lower solar resources but I can call this cherry picking

That's just the first town I saw on the Minnesota page that was colder. The pages were alphabetical and it was a town starting with an A.  I'm sure there are many others. In fact there are several towns in many of the northern US states (and state with high altitudes like Colorado) with temps that are essentially just as cold as yours.

But of course I only had to point out one to disprove your prior statement

It's ok.   I agree that you live in a very cold place and it's impressive what you've done with your energy conservation measures and I have no doubt given the relatively abundant sunshine you have that with enough thermal storage you can get enough PV up to supply all your energy needs.  Just realize that yours in not the worst case scenario.

I guess most people living offgrid have enough land for a large ground mount PV array.

The issue is not acreage.  Many if not most people off grid do not live in the open plains like you do. Trees are a major factor in much of the rural USA.  Local topography - mountains and hills can also limit solar exposure. Even if I cut down all the trees around my home, I would still only have about 4 hours of potential direct sun exposure in the dead of winter due to a mountain ridge to the south of me.

Many people who live off grid live in the forest and/or mountains.

All other energy sources will be way more expensive when you take the entire system in to account.

Again, I think you are overselling it.  Heating with wood is very economical (sometimes almost free) in many locales and in those places PV will never compete on price. With propane prices so low - propane heat is also very cheap and if prices stay low PV will only beat it on price with a very long term amortization.  And yes, in a few select locations wind or microhydro will be cheaper. Using the words "All" and "way more" is hyperbole.

I agree that solar PV energy prices will only get lower and that it will continue to see wider and wider adoption. But it is no Panacea.

[CatalinaWOW]

Is unfortunate that you have bad access to solar but from what you say that seems a as a grid connected house and live in some sort of urban area. There is always the possibility to move to a location with better solar access
Most house in urban areas are large and not properly insulated (just minimum by local code) so the surface of the PV array needed to provide 100% of the energy will be high and most likely the space for that will not exist (small lots in urban area).
While solar PV is cheapest it will not work in any place because of this limitations mentioned and probably others.
There is no doubt in my mind that solar PV will probably be the dominant energy source in 10 to 15 years and many things will change with this.

You are again projecting your assumptions on others.  Yes, my house is grid connected.  Which is fortunate, because it would be quite difficult to work this location off grid.  It is well insulated, and in a milder climate than you have in Saskatchewan, but it is still difficult.  Is it an urban area?  Definitions differ.  According to the zoning it is exclusively agricultural use.  It is 17 miles from the nearest edge of a small (less than 100k people) city.  I am dependent on wells and septic systems for water and sewer and satellite for internet.  I can see neighbors houses (in winter when the deciduous trees have lost their leaves), but it is 150 meters to the street.  The neighbors raise various crops for income.  Most would call it rural.  At best it is exurban.  It is a large enough lot that from an engineering standpoint I could clear trees for an array.  But environmental rules say I can't cut more than six trees without replacing them.  All of my wood cut for burning is replaced with new trees.  Yea sustainability.

My case isn't representative, any more than your location in Saskatchewan is representative, but it is a common situation.  If you look at population censuses, the great plains of North America have some of the lowest population densities on the continent.  Large numbers of people live in exurban, hilly and wooded zones.

I could move to a more favored location for solar, but as I mentioned in the earlier post, that is not a general solution.  Everyone cannot live in favored solar locations.  If many people try, the cost of those locations will rise (and that cost increase should be included in the cost of solar).

I have no doubt that solar will grow in importance.    In most countries it will become one of the major elements of the energy mix.  But until storage becomes a great deal better, or until some really huge investments in infrastructure (house insulation, distribution and other things) are made it will not be dominant.  I don't see that happening in just twenty years.  That is consistent with your own dismissive observations about the current urban infrastructure (where most energy is used).  Until all those houses are rebuilt with better insulation and lower energy needs and support for the most possible solar installation they will be dependent on bulk energy sources.  Some of which will be solar, but even that will require massive investments.  Those investments will occur as current investments wear out, or when the ongoing economic differential grows so large that it justifies losing existing investments.  Solar isn't that good yet.

[electrodacus]

You are again projecting your assumptions on others.  Yes, my house is grid connected.  Which is fortunate, because it would be quite difficult to work this location off grid.  It is well insulated, and in a milder climate than you have in Saskatchewan, but it is still difficult.  Is it an urban area?  Definitions differ.  According to the zoning it is exclusively agricultural use.  It is 17 miles from the nearest edge of a small (less than 100k people) city.  I am dependent on wells and septic systems for water and sewer and satellite for internet.  I can see neighbors houses (in winter when the deciduous trees have lost their leaves), but it is 150 meters to the street.  The neighbors raise various crops for income.  Most would call it rural.  At best it is exurban.  It is a large enough lot that from an engineering standpoint I could clear trees for an array.  But environmental rules say I can't cut more than six trees without replacing them.  All of my wood cut for burning is replaced with new trees.  Yea sustainability.

My case isn't representative, any more than your location in Saskatchewan is representative, but it is a common situation.  If you look at population censuses, the great plains of North America have some of the lowest population densities on the continent.  Large numbers of people live in exurban, hilly and wooded zones.

I could move to a more favored location for solar, but as I mentioned in the earlier post, that is not a general solution.  Everyone cannot live in favored solar locations.  If many people try, the cost of those locations will rise (and that cost increase should be included in the cost of solar).

It seems that you have quite a bit of land is just that is all forest.  Most of the US surface is not covered by forest and also large surface is not populated so I do not think land will ever be a problem.
And I agree that most people all over the globe live in urban areas where my solution may not work especially since most houses have bad thermal insulation and need large quantities of energy for heating thus requiring large PV arrays.
US is extremely fortunate in therms of solar especially when compared to most European countries. 

I have no doubt that solar will grow in importance.    In most countries it will become one of the major elements of the energy mix.  But until storage becomes a great deal better, or until some really huge investments in infrastructure (house insulation, distribution and other things) are made it will not be dominant.  I don't see that happening in just twenty years.  That is consistent with your own dismissive observations about the current urban infrastructure (where most energy is used).  Until all those houses are rebuilt with better insulation and lower energy needs and support for the most possible solar installation they will be dependent on bulk energy sources.  Some of which will be solar, but even that will require massive investments.  Those investments will occur as current investments wear out, or when the ongoing economic differential grows so large that it justifies losing existing investments.  Solar isn't that good yet.

I think thermal storage is the best solar energy solution and I hope this will be adopted more. People up to now mostly where using PV solar for electricity needs not heating.
As seen in the IEA document most of the house energy is used for heating and hot water and there thermal storage makes the most sense since is extremely inexpensive and I do not think electrochemical battery will ever be able to compete with thermal storage.
When searching for an energy source to power my house I looked at all available options and my main criteria of selection was low cost.
Solar installations around the globe has an exponential growth for the past  10 to 15 years with doubling installed capacity almost each two years.
Solar PV already exceeded 1% of total energy needs back in 2015 https://cleantechnica.com/2015/06/12/solar-power-passes-1-global-threshold/
If the trend continues all is needed are 6 or 7 doubling to get to 100% that is around 15 years if trend continues with doubling installed capacity each 2 years.
Yes the trend will slow down probably that is why I mentioned over 50% of the electricity provided by solar in 10 to 15 year.

Again, I think you are overselling it.  Heating with wood is very economical (sometimes almost free) in many locales and in those places PV will never compete on price. With propane prices so low - propane heat is also very cheap and if prices stay low PV will only beat it on price with a very long term amortization.  And yes, in a few select locations wind or microhydro will be cheaper. Using the words "All" and "way more" is hyperbole.

I agree that solar PV energy prices will only get lower and that it will continue to see wider and wider adoption. But it is no Panacea.

I disagree that heating with wood is more economical than both PV heating and natural gas (where that is available and at the current price).
Cost amortization for my particular cost is as mentioned before $264/year for the heating part so try to imagine how will that be competitive with wood where you need to amortize the EPA rated stove and all the work needed o collect the wood cutting and storing.
My house will need about one cord of wood (4000lb) ~ 2000kg for per year assuming a good 70% efficient EPA rated stove.
If I where to buy that wood here it will cost a bit more than $264 (cost amortization of PV solar heating) and that is just the wood no storage space and stove amortization cost plus time spent and maintenance. 

[mtdoc]

Again, I think you are overselling it.  Heating with wood is very economical (sometimes almost free) in many locales and in those places PV will never compete on price. With propane prices so low - propane heat is also very cheap and if prices stay low PV will only beat it on price with a very long term amortization.  And yes, in a few select locations wind or microhydro will be cheaper. Using the words "All" and "way more" is hyperbole.

I agree that solar PV energy prices will only get lower and that it will continue to see wider and wider adoption. But it is no Panacea.

I disagree that heating with wood is more economical than both PV heating and natural gas (where that is available and at the current price).
Cost amortization for my particular cost is as mentioned before $264/year for the heating part so try to imagine how will that be competitive with wood where you need to amortize the EPA rated stove and all the work needed o collect the wood cutting and storing.
My house will need about one cord of wood (4000lb) ~ 2000kg for per year assuming a good 70% efficient EPA rated stove.
If I where to buy that wood here it will cost a bit more than $264 (cost amortization of PV solar heating) and that is just the wood no storage space and stove amortization cost plus time spent and maintenance.

You're generalizing your situation to others. A cut and split cord of wood costs $200 delivered here.  But the people I know who live off grid (and others)often get a free ($20 some juristictions) permit which allows them to cut 4-6 cords of wood a year on state or national forest land.  Others have enough wood on their property.   Storage of wood is free for most people - they already have woodshed/tarps/porch etc.

Also, in addition to the cost of extra PV panels, are you including the cost of more battery and/or thermal storage?  How about the cost of extra charge controller, wire, combiner box, etc to deal with the additional PV input?  What about the cost of mounting the panels?  Those things also have maintenance and eventual replacement costs.

Just because something makes economic sense for your situation does not mean it will apply to others.

[electrodacus]

You're generalizing your situation to others. A cut cord of wood costs $200 delivered here.  But the people I know who live off grid (and others) buy a $20 permit which allows them to cut 4 cords of wood on national forest land.  Others have enough wood on their property so they only have to pay for a bit of chainsaw fuel and maintenance.  Storage of wood is free for most people - they already have woodshed/tarps/porch etc.

Also, in addition to the cost of extra PV panels, are you including the cost of more battery and/or thermal storage?  How about the cost of extra charge controller, wire, combiner box, etc to deal with the additional PV input?  What about the cost of mounting the panels?  Those things also have maintenance and eventual replacement costs.

Just because something makes economic sense for your situation does not mean it will apply to others.

$200 for a cord is good (better than here for sure) but still that is not all as mentioned and the $20 for permit is also fine but you need to work to get that wood cut and transported. The stove can also be a significant cost and needs maintenance and replacements.
My calculation includes all parts needed PV, cables, battery, thermal storage, controllers, heating cables,LiFePO4  battery .... as you can see in more details in my presentation. Also the replacement battery and inverter was included in the cost as mentioned in one of the above posts.
No extra charge controller is needed the DMPPT450 and SBMS120 are designed for a minimum 25 years life and they do not contain any parts that degrade (there are no electrolytic capacitors used). Also the cost is realy low for those and represent a very small percentage of the total cost (usually less than 5%)
And yes you are right about me not including the installation cost since I will be doing that. But that time is once in the beginning no other work needed for the next 25 years and there should be no maintenance other than replacing the battery once every 10 years or so and eventually the inverter none of this two are related to the heating part since the heating needs no LiFePO4 battery or inverter.
The heating part is made out of only PV panels, cables, DMPPT450, heating cables and thermal mass none of this have any maintenance or replacement needed for more than 25 years (can be 50 years).
PV panels will degrade maybe at a rate of less than 0.5% per year (my first panels have already more than 5 years and I can not realy say if there is a degradation in output it will be difficult to measure).

[cmhansen]

A cut and split cord of wood costs $200 delivered here.

I'm going to go 'out on a limb' and say that's pine and not oak.  The time you don't spend chopping or feeding any wood for that matter will be spent cleaning up ashes.  And, firewood is never going to be as dry as you want it.

You can use 100% solar even in Alaska, the panels just need to be on a HVDC line a couple thousand miles south or so, say a solar plant in sunny SK.  Keep the battery local.  Plus for EVs anywhere, some centralized generation is needed to charge on the go, or even at home really.  I suppose you could get 100kWh out of a 20kW array if you have a very sunny day, but that's a whole day's worth for just one car.

[mtdoc]

A cut and split cord of wood costs $200 delivered here.

I'm going to go 'out on a limb' and say that's pine and not oak.  The time you don't spend chopping or feeding any wood for that matter will be spent cleaning up ashes.  And, firewood is never going to be as dry as you want it.

No pine here. All Doug Fir, Alder, Hemlock, and some maple. When I lived in Vermont $200 would get you a cord of good Eastern hardwood. Exceptional heat content.

Ashes and dry wood is no issue at all. Our stove burns so efficiently, I only need to shovel out ashes every 2 cords or so. That takes about 2 minutes tops. Dry wood is easy. Use seasoned wood, cut, properly stacked and covered. No biggie.

I suppose it seems like a big deal to someone with no experience heating with wood but it's like any other regular household task - washing dishes, clothes, sweeping floors, watering the garden - or clearing snow off the solar panels and maintaining the battery bank...

[electrodacus]

You can use 100% solar even in Alaska, the panels just need to be on a HVDC line a couple thousand miles south or so, say a solar plant in sunny SK.  Keep the battery local.  Plus for EVs anywhere, some centralized generation is needed to charge on the go, or even at home really.  I suppose you could get 100kWh out of a 20kW array if you have a very sunny day, but that's a whole day's worth for just one car.

Alaska has better solar resources than Germany so solar PV is not realy a problem there.
Yes cars need a lot of energy and I do not have any good solution for that. A car is usually not at home during the day and charging an EV battery from another battery is a realy bad idea in therms of cost amortization.
In fact as of now battery cost amortization on EV is so high that makes them more expensive to drive than gasoline cars.
I do not drive much and for now I will stay with my gasoline car and I hope that in near future the self driving cars (level 5 autonomy) will make owning a car obsolete and ordering a car at any time more convenient and cost effective at least for me since I do not need to drive much.
With the 10kW PV array in SK I have an annual average generation of 42kWh/day with some particularly good sunny days in spring exceeding 70kWh/day
My driving needs are low about once a week a 150km drive that is around 38kWh (less in summer depending on EV) or about 152kWh/month and I can probably get that easy from the 10kW PV array if needed (a bit harder in the 3 winter months but no problem in the other 9 months).

[mtdoc]

I have a Chevy Volt and rarely use any gas in it ( i rarely drive more than 30 miles in a day). Its cost to operate is way less tban our gas cars. In the summer i can charge it with excess PV production. 12 kWh gets me 30-40 miles.  Battery amortization is a non issue. The new purchase price was no more than a similiarly equiped gas only car. Maintenance costs are much less since oil and brake costs are minimal. Battery replacement in 10-15 years will cost no more than what ICE tune ups, timing belt replacements, oil changes, etc would have cost.

We will be replacing my wifes's Volvo with a Chrysler Pacifica PHEV this spring.

Some parts of Alaska have good solar insolation in the summer months but forget about it in the winter. In northern Alaska there is few hours of potential sun (or none!). Even in the south were there is a few more hours of sun potential it is often cloudy. Try looking at PV Watts data for SE Alaska in the winter.....

[electrodacus]

I have a Chevy Volt and rarely use any gas in it ( i rarely drive more than 30 miles in a day). Its cost to operate is way less tban our gas cars. In the summer i can charge it with excess PV production. 12 kWh gets me 30-40 miles.  Battery amortization is a non issue. The new purchase price was no more than a similiarly equiped gas only car. Maintenance costs are much less since oil and brake costs are minimal. Battery replacement in 10-15 years will cost no more than what ICE tune ups, timing belt replacements, oil changes, etc would have cost.

We will be replacing my wifes's Volvo with a Chrysler Pacifica PHEV this spring.

Some parts of Alaska have good solar insolation in the summer months but forget about it in the winter. In northern Alaska there is few hours of potential sun (or none!). Even in the south were there is a few more hours of sun potential it is often cloudy. Try looking at PV Watts data for SE Alaska in the winter.....

I'm not very familiar with Chevy Volt but it seems it has a starting msrp of $33k vs a malibu starting msrp $22k so I think there is a premium that you pay for the battery and electric motor.
Trying to amortize that will be impossible with the current gasoline price.
In any case an EV will need a battery for energy storage while the gas tank on ICE is almost free. Cost amortization for that battery (with current prices of those batteries) will make an EV more expensive to drive.

A 10kW array 60 degree tilt in Berlin will only produce 8348kWh in a year while same in Anchorage Alaska 9013kWh while winter months production are almost the same.

[mtdoc]

I'm not very familiar with Chevy Volt but it seems it has a starting msrp of $33k vs a malibu starting msrp $22k so I think there is a premium that you pay for the battery and electric motor.

1- The Volt is a completely different class of car than a Malibu.  Perhaps comparing the full EV Chevy Spark would be comparable - it's MSRP starts at 25K  but after tax rebate it would be $17.5K

2- I paid 32.5 K for my Volt out the door and it has the premium (leather) trim and back up camera.  After $7.5 K tax rebate it cost me 25K.

An equivalent ICE car would cost more so there is nothing to amortize. As I pointed out given the lower operating costs it's a no brainer.

while winter months production are almost the same.

   Winter production is not even close to summer!!!.  How could it be given how short the days are in the winter?   (add:) Maybe you meant compared to Berlin? -Irrelevant to me - and not part of my prior post - I was stating the fact that winter production in AK is very poor. Here's the data from PV watts   As you can seen the winter months production is between 1/8th and 1/3rd of summer.  Barely enough to keep lights and  a refrigerator on. And that is assuming you keep the panels free of snow at all times.

[electrodacus]

I'm not very familiar with Chevy Volt but it seems it has a starting msrp of $33k vs a malibu starting msrp $22k so I think there is a premium that you pay for the battery and electric motor.

1- The Volt is a completely different class of car than a Malibu.  Perhaps comparing the full EV Chevy Spark would be comparable - it's MSRP starts at 25K  but after tax rebate it would be $17.5K

2- I paid 32.5 K for my Volt out the door and it has the premium (leather) trim and back up camera.  After $7.5 K tax rebate it cost me 25K.

An equivalent ICE car would cost more so there is nothing to amortize. As I pointed out given the lower operating costs it's a no brainer.

Like I mentioned I'm not an expert in cars but I think that Malibu was equivalent since seems the same class of car from same manufacturer and just the 1.5liter ICE so without the battery and electric motor on the Volt.
Just made a quick search and it seems a better comparison will be Chevrolet Cruze at $19656 and you can read here about operating cost and payback https://en.wikipedia.org/wiki/Chevrolet_Volt

  Winter production is not even close!!!.  How could it be given how short the days are in the winter?  Surely as an engineer your understand this..     Here's the data from PV watts   As you can seen the winter months production is between 1/8th and 1/3rd of summer.  Barely enough to keep lights and  a refrigerator on.

Winter months in Anchorage have the same amount of solar as in Berlin Germany and that is what I was saying with this: "A 10kW array 60 degree tilt in Berlin will only produce 8348kWh in a year while same in Anchorage Alaska 9013kWh while winter months production are almost the same."

[mtdoc]

Winter months in Anchorage have the same amount of solar as in Berlin Germany and that is what I was saying with this: "A 10kW array 60 degree tilt in Berlin will only produce 8348kWh in a year while same in Anchorage Alaska 9013kWh while winter months production are almost the same."

OK - yeah - I read you post initially as claiming winter months was the same as summer - since that was my earlier point (nothing in my post about Berlin). Once I realized my error I edited my post but too late!

The comparison to Berlin is irrelevant to me and was not part of my prior posts. My point has continued to be that winter PV production is very low in AK and many other places - making any reasonable sized array insufficient to supply all one's energy needs in winter. Farther south - in the mid northern latitudes - such as were you live it could work- but even then only in the most extreme cases - i.e. very small, very will insulated home with lots of thermal storage - in a location with relatively good solar insolation.

[electrodacus]

Winter months in Anchorage have the same amount of solar as in Berlin Germany and that is what I was saying with this: "A 10kW array 60 degree tilt in Berlin will only produce 8348kWh in a year while same in Anchorage Alaska 9013kWh while winter months production are almost the same."

OK - yeah - I read you post initially as claiming winter months was the same as summer - since that was my earlier point (nothing in my post about Berlin). Once I realized my error I edited my post but too late!

The comparison to Berlin is irrelevant to me and was not part of my prior posts. My point has continued to be that winter PV production is very low in AK and many other places - making any reasonable sized array insufficient to supply all one's energy needs in winter. Farther south - in the mid northern latitudes - such as were you live it could work- but even then only in the most extreme cases - i.e. very small, very will insulated home with lots of thermal storage - in a location with relatively good solar insolation.

I will not recommend someone in Anchorage Alaska to do solar PV heating unless the other energy sources are quite expensive. It is warmer there than at my location but still colder than Berlin Germany so it will depend on the prices of other energy sources like Natural Gas.
In Germany is not as cold and the cost of other energy sources is high enough that a PV heating will make economic sense but a lot of space will be needed depending on house size and energy needs.
There are houses there (in Germany) with better thermal insulation than mine so much so that even the heat from the appliances can keep the house warm.

[cmhansen]

I suppose it seems like a big deal to someone with no experience heating with wood but it's like any other regular household task - washing dishes, clothes, sweeping floors, watering the garden - or clearing snow off the solar panels and maintaining the battery bank...

At least the point got across there's a great deal of variation under the term 'firewood'.  If chores are 'no biggie', why not go horse and buggie??  And forget chainsaws / hydraulic splitters / etc and go back to just an axe for that matter.  Trade in the tractor for a hoe, after all it will 'warm you twice!'

[mtdoc]

I suppose it seems like a big deal to someone with no experience heating with wood but it's like any other regular household task - washing dishes, clothes, sweeping floors, watering the garden - or clearing snow off the solar panels and maintaining the battery bank...

At least the point got across there's a great deal of variation under the term 'firewood'.  If chores are 'no biggie', why not go horse and buggie??  And forget chainsaws / hydraulic splitters / etc and go back to just an axe for that matter.  Trade in the tractor for a hoe, after all it will 'warm you twice!'

Well, in spite of the hyperbole, the fact is it really is not that much work to heat with wood if you buy the cut and split wood.  I know several elderly people (70s and 80s) who do it.  It takes maybe 10 minutes a day in total to bring wood in, load the stove, tend to the fire and occasional ash removal (which just takes a couple of minutes once a month or so)

If one chooses to cut, haul,  and split their own wood then that does involve some regular physical labor - I'd guess maybe 4-6 hours for a cord if you know what you're doing.  But nothing wrong with hard work - it's good for the mind and body (and cheaper than a gym membership!).  And in that case the wood does  warm you multiple times then!  I've done it in the past but these days I mostly buy my wood unless I'm cutting and splitting downed trees on my property.  With a good wood supply my wife and young kids have no problem keeping our home warm with minimal effort, even if the power is out and there is no sun.

[HackedFridgeMagnet]

sry if off topic. will get back to it soon.
I guess a cord is some quantity of wood, how much? Here we say we buy by the tonne but really it is by volume. Locally it is about  US$50 per cubic metre split and delivered.
My neighbour cuts my fallen trees and gives me 1/3 cut and split, it's a great deal for both of us.
Love having a fire going in the living room. Though it is a bit messy.

I am thinking of getting some solar but I may as well do a grid connect, and synch the heaters to run when the sun is shining, as we only get a 7c per kWh for generated energy.
Then put enough insulation and thermal mass into the house to make the best of it. 

[electrodacus]

sry if off topic. will get back to it soon.
I guess a cord is some quantity of wood, how much? Here we say we buy by the tonne but really it is by volume. Locally it is about  US$50 per cubic metre split and delivered.
My neighbour cuts my fallen trees and gives me 1/3 cut and split, it's a great deal for both of us.
Love having a fire going in the living room. Though it is a bit messy.

I am thinking of getting some solar but I may as well do a grid connect, and synch the heaters to run when the sun is shining, as we only get a 7c per kWh for generated energy.
Then put enough insulation and thermal mass into the house to make the best of it.

It is not off topic since we discus the comparison with other sources of energy and is good for people to have an idea of how to compare them.

I'm also new to the cord as unit of measurement (I'm used with metric) and this measurement refers to volume (not very precise same as with cubic meter) since it depends how densely packed the wood is and also what type of wood.
If I'm wrong then someone will correct me but a cord of wood is 8ft x 4ft x 4ft and that will be 128 cubic feet or about 3.62 cubic meter (so your price of $50/m3 is not bad).
Again this is volume 128 cubic feet and actual volume of wood will be less around 85 cubic feet since there is a lot of air in there
I used this source https://en.wikipedia.org/wiki/Cord_%28unit%29
Also from there and confirmed with other sources you get 6477kWh of energy from that wood (seasoned dried read oak). And with a fairly ideal high efficiency stove with 70% efficiency you get around 4500kWh of usable heat and that is exactly what my house needs in an average winter season here.

Assuming you can get one cord of this quality wood for 200USD / 4500kWh = 4.4 cent is the cost of unit of energy and that is higher than natural gas at my location that is why I used natural gas in my comparison with solar PV.

[CCitizenTO]

It is shocking when you see systems like http://www.sunbandit.us/ selling almost a conventional water heater in excess of $9,000 for the system. Just how does that pay off?  It is a conventional water heater with one extra heater for grid connect (3 total) a couple of panels and enphase converters.  I heat water with PV and the home made PWM converter to keep the panels at power point only costs about $25. Failing to keep the panels at power point will result in 50% power loss.  Your basic cost is almost just the panels.  If you design the system as supplemental heating and use only the lower heating element for PV, nearly 100% of the panels potential power generation is used 365 days a year. That surpasses almost anything else you can do with PV at a much lower hardware cost.  $500 for just two panels is a cheap way to get into solar.  Shamefully simple.  Just a nano,  a couple FET and some capacitors as the storage bank.

Well a home-made solution may work for you. However, when you start to deal with the scale that mass marketing requires you have to deal with testing, certifications, building code compliance (Electrical, Plumbing, Gas, etc...) and probably a ton of other bullshit to basically declare that it's safe to use in someone else's home on top of the money for setting up a corporation so if your thing does burn someone's house down you don't lose everything. All those cost money and someone isn't going to do something like this at cost so they're going to want to turn a profit and they'll try and get as much money as the market will bear.

[foursquare]

Hi Electrodacus,

We never thought this was possible, but it now is. It's amazing how science has brought us beyond our expectations. Back during the times, nobody even thought electricity would exist, and now, there are solar panels that can convert solar power into electricity.

[Seekonk]

The sunbandit utilizes all available UL rated components that you can buy for less than $3,000.  They don't actually make anything but the label.

electrodacus, you may be in violation of U.S. Pat. No. 5,293,447 for your switched resistance heating system.  Watch out for trolls.

[hendorog]

The sunbandit utilizes all available UL rated components that you can buy for less than $3,000.  They don't actually make anything but the label.

electrodacus, you may be in violation of U.S. Pat. No. 5,293,447 for your switched resistance heating system.  Watch out for trolls.

IANAL but don't patents expire after 20 years? That was filed in 1992.

[electrodacus]

The sunbandit utilizes all available UL rated components that you can buy for less than $3,000.  They don't actually make anything but the label.

Yes all those components are off the shelf they do not seems to have anything other than offer a complete package.

electrodacus, you may be in violation of U.S. Pat. No. 5,293,447 for your switched resistance heating system.  Watch out for trolls.

I just checked that and while is a bit vague and hard to understand (probably as most patten applications) seems possible to be something similar to part of what I do in the DMPPT.
Still if this is the same idea I use it is funny that someone will allow such a simple idea to be patented.
Anyone with basic knowledge about electricity can come up with this idea on their own in a few minutes since is nothing more than simple Ohm's law involved.
How did you found that patent ?
The patten seems rally old also more than 20 years.

[Seekonk]

There are a lot of PV water heating patents.  Each are as vague as the next. There is another one that says "any adaptive control."  That covers a lot.  USPTO doesn't work like it used to.  Google search seems to have taken that searching over. I just did a search for "photovoltaic water heater." So, you can just invent an "unspecified control system."

[electrodacus]

There are a lot of PV water heating patents.  Each are as vague as the next. There is another one that says "any adaptive control."  That covers a lot.  USPTO doesn't work like it used to.  Google search seems to have taken that searching over. I just did a search for "photovoltaic water heater." So, you can just invent an "unspecified control system."

That patent you mentioned while a bit confusing to read seems to be fairly similar to the DMPPT heating part (the DMPPT combines that also with battery charging).
The idea was useless at that time since PV panels where much more expensive than  thermal solar panels.
In any case that is an old patent and hendorog mentioned above that one is expired since it has more than 20 years since the application was made in 1992.
That is maybe a good thing since I think an idea that had a patten and expired can not be patented again. (not sure that is just what I think makes sense)
I will never patent any of my ideas since I find that a waste on money and resources from my part and hinder progress in general (my opinion).

[CatalinaWOW]

USPTO screws up a fair amount.  I have heard that the Field Effect Transistor was patented three times, twice before it could be fabricated.  Once in the first decades of the twentieth century, and a second time before WWII.  Unless you are planning to hire an army of lawyers to defend your turf, the patent system is best left to the large corporations to play their games with.

[moz]

I am thinking of getting some solar but I may as well do a grid connect, and synch the heaters to run when the sun is shining, as we only get a 7c per kWh for generated energy.

We get 5c, but feed the grid anyway because the net benefit is significant. If nothing else the panels shade the roof in the summer The way the market is at the moment the net install cost after selling the RECs is very low. Although one tip: if you have tiles on the roof I suggest looking art replacing them with insulated steel before putting up PV. Tiles are awful, especially old clay tiles.

Then put enough insulation and thermal mass into the house to make the best of it.

That's where you can win big. Australian houses make me cry, there's so many easy wins left on the table. Sadly most of them are nigh on impossible to retrofit - albeit sometimes only because the local government won't let you... or you won't be able to sell the house "because it looks funny". Maybe not an issue for most, but it is for us.

We ended up building a "shed" on the western/back side of the house that is well insulated, but also shades some of the exposed brick walls which helps a lot with summer cooling. Having that as a refuge room on hot days is almost magic - the modern split system aircon uses about 500W to keep that room 20 degrees cooler than outside, and we have ~3kW of PV being generated on those days. Turning aircon off as the sun goes down doesn't hurt much, and if we did it again I'd go for a much thicker, more insulated slab underneath and have a pipe to divert the aircon output through the slab to pre-cool it for the overnight. Half a metre high concrete box full of gravel, pump air in one side and draw it out the other as a "cool store".

Also, in Oz it's usually cheaper and more efficient to have a solar hot water storage system than PV plus heat pump. We have good local skills in the area and while maintenance is a little higher (heat pump HWS fail too!) the roof space and dollars required is significantly lower ($4k rather than $10k for us)