PV energy less expensive than natural gas.

[DougSpindler]

Impressive system.

[Marco]

Keep in mind my system total cost was $15K and climate is fairly harsh with average temperature for January -16.7C thus an air to air heat pump will not work

I'm not familiar with many heatpump systems, but one caught my eye a while back so I'll use that ... Chiltrix. At those kind of temperatures it claims >4 kW of heating power with a LWT of 35 degrees which might be sufficient for you with floor heating given the thorough insulation. Reasonably priced as well.

Still might not be economical regardless of course.

[electrodacus]

Keep in mind my system total cost was $15K and climate is fairly harsh with average temperature for January -16.7C thus an air to air heat pump will not work

I'm not familiar with many heatpump systems, but one caught my eye a while back so I'll use that ... Chiltrix. At those kind of temperatures it claims >4 kW of heating power with a LWT of 35 degrees which might be sufficient for you with floor heating given the thorough insulation. Reasonably priced as well.

Still might not be economical regardless of course.

Here is the spec for CX34
As mentioned my average temperature for January is -16.7C (that is average so I typically have sunny days that are the coldest with -20C to -30C during the day and up to -40C occasionally during the night the cloudy days are typically warmer maybe -10C during the day and -15C at night)
The in floor heating will not require high temperatures but at least 45C to 50C is needed to be able to push the necessary power same with low temperature thermal water storage that will be limited to +55C
Now the table spec linked above is unfortunately in Fahrenheit but 122F is 50C and that requires at least +5F  that is -15C outside ambient temperature and with those conditions COP is 1.74 supposedly not very likely in real world (not lab tests).
Even with much better conditions COP is not much over 2 that means max heat output is around 4 to 5kW (not the case at my location in January but maybe end of February or March) and currently I get 8 to 10kW peak heat in the afternoon when is sunny so that means I will need two of this CX34 heat pumps in order to reduce my PV array size to half thus a cost of around $8000 just for the heat pump there are some other components that are needed like a heat exchangers ans some water pumps and also a much larger inverter and a much larger battery to deal with the higher load of the compressors and battery will need to be much larger as the PV array will be reduced see below.

Now I estimate a minimum extra cost of $8000 for the heat pumps maybe another $2000 for heat exchangers, pipes and few water pumps then not sure at least 3000 to $4000 for a large enough inverter to deal with this heat pumps and another $2000 to $4000 to at least double or triple the battery capacity so just an insane amount of money and will not even work in January at my location.

Now the savings from from those $15k PV heating system assuming this will work maybe in a milder climate will be by reducing the PV array to half and that will be around $4000 saving but heat pump and the rest of equipment will cost at least 12k to 18k so huge amount of extra cost with no benefit making the system more complex and much less reliable.

[cdev]

The economics of using a PV system for heating may become much more favorable in the years ahead if the price of other fuels increases a lot as expected.

[electrodacus]

The economics of using a PV system for heating may become much more favorable in the years ahead if the price of other fuels increases a lot as expected.

The point I try to make is that PV heating is already the most cost effective heating source and there is no need for fuels prices to increase.
This is tanks to low cost of PV panels as mentioned just 2 cent/kWh together with low cost thermal storage less than 1 cent/kWh

[coppice]

The economics of using a PV system for heating may become much more favorable in the years ahead if the price of other fuels increases a lot as expected.

The point I try to make is that PV heating is already the most cost effective heating source and there is no need for fuels prices to increase.
This is tanks to low cost of PV panels as mentioned just 2 cent/kWh together with low cost thermal storage less than 1 cent/kWh

I wonder how many people have a climate where this would work?

[Marco]

Even with much better conditions COP is not much over 2 that means max heat output is around 4 to 5kW (not the case at my location in January but maybe end of February or March) and currently I get 8 to 10kW peak heat in the afternoon when is sunny so that means I will need two of this CX34 heat pumps in order to reduce my PV array size

That's not necessarily how'd you use it. Ideally you'd use it to heat the water storage tank and then just use any surplus electrical power to do the same. Though I'll admit, unless you need the AC in the summer it doesn't really make sense.

[electrodacus]

I wonder how many people have a climate where this would work?

I will say at least 90% of the world if not more has climate where this will not just work but also be more cost effective than any other source.
My location is relatively sunny (sort of average) and about as cold as it gets.

Moving my house and system to many location around the world will still work as it is with some exception's in northern Europe where a slightly larger PV array will be needed but since competing energy sources like natural gas are more expensive there it will still make PV the most cost effective.
For a new house build is even more so as connecting a new house to utilities like electricity and natural gas may cost as much or more than the entire solar system at least for a small house like mine.
Old existing house have the problem that they are improperly insulated meaning they will need a large ground mount array and they may not have the space for such a large array and they may also have large trees or building and so no good access to sun.

Finding things to do with the excess energy may even generate so profit making heating and electricity free or even profitable. For now I have at least 50% of the energy unused in an average year, with as much as 90% unused energy in summer.

That's not necessarily how'd you use it. Ideally you'd use it to heat the water storage tank and then just use any surplus electrical power to do the same. Though I'll admit, unless you need the AC in the summer it doesn't really make sense.

Not sure I understand what you mean.
As one unit uses 2.5kW and outputs say 5kW at a COP of 2 and the PV array provide 5kW then in order to take advantage of all available energy when is available you will need two of this units so that in a sunny afternoon you charge the thermal mass storage with a 10kW rate that is the same sate that I have now. Not using the solar energy when is available means lost energy.

The current setup with direct PV heating and a 10KW PV array plus 158kWh thermal storage provide full house heating in worst case scenario. So the only reason to use a heat pump will be if it will reduce cost and so thermal mass storage capacity will need to remain the same and the only way to reduce cost is to reduce the PV array size as mentioned reducing that to half of current size so 5kW PV array instead of 10kW will save about $4000. Then assuming the heat pump can get an average COP of 2 the same amount of heat can be transferred to thermal storage but since that particular heat pump takes about 2.5kW and outputs 5kW (COP of 2) two of them will be needed to achieve 10kW heat output to be equivalent with direct PV heating and larger PV array.

Result was that to add a heat pump even in a very optimistic use case will result in much higher cost not to mention PV panels will last a minimum 30 years where that heat pump may need replacement every 10 to 15 years depending on quality so even more expensive to the absurd likely it will cost 3x as much to include a heat pump and the only advantage will be needing less pace for the PV array.

[Marco]

Just because you are heating a water tank with the heat pump, doesn't mean you can't also throw a heating coil in it. So when you have 5 kW, you can use 2.5 kW for the heat pump and 2.5 kW for the coil ... when you have 2.5 kW you use it all for the heat pump.

It could work to make the most out of your power when there is the least of it. Of course the coil can work at any power, the heat pump will need to be run off battery with a duty cycle when the solar panels can't power it ... so it causes more headaches.

[electrodacus]

Just because you are heating a water tank with the heat pump, doesn't mean you can't also throw a heating coil in it. So when you have 5 kW, you can use 2.5 kW for the heat pump and 2.5 kW for the coil ... when you have 2.5 kW you use it all for the heat pump.
It could work to make the most out of your power when there is the least of it. Of course the coil can work at any power, the heat pump will need to be run off battery with a duty cycle when the solar panels can't power it ... so it causes more headaches.

It will not workout as if I reduce the PV array size in half I will need multiply that with 2 so all energy sent to heating will need to be trough a heat pump with COP of 2 else I can not reduce the PV array to half I can probably reduce the PV array to 7.5kW and then use just a single heat pump but then the economics are still as bad.

In the colder winter months like January I use all the energy available from the 10kW PV array and store the excess in thermal mass storage then in cloudy days I take some of the energy from PV array the little that is available and the rest from the thermal storage.
Both PV and thermal storage are so inexpensive than adding a heat pump will not make any economic sense.
Heat pumps can not be cost effective when energy generation cost and energy storage cost is so low. Even with high energy costs as is the case of grid electricity of 15 to 20cent/kWh it will barely break even in best case scenario but this is a different subject.
My system as it is provides all the energy needed and in order to add a $4000 heat pump plus many more thousand $ in accessory you need to be able to reduce that from the current $15k investment and as mentioned the only part that can be reduced is the PV array size and that is so cheap and has such a low cost amortization that  even if heat pump is free it will not be able to be a good investment as it needs some additional equipment as mentioned in order to integrate that heat pump in to the system.

Maybe you did not understood the LiFePO4 in this equation that is not used for the heating part but for providing electricity to the house and that battery is 5kWh only large enough to provide the house with energy over night as the large 10kW PV array will produce a minimum of 4kWh of energy in the worst overcast / snowy day like today and that is enough to cover the house needs that is an average of around 120kWh/month but if PV array size is to be reduced to say half then battery capacity will need to be increased about 3x to deal will prolonged overcast of 5 to 6 days and also to be able to support a larger inverter and buffer the heat pump needs thus battery capacity increase alone will cost another $4000 completely negating reducing the PV array to half.  So even if heat pump and all the accessories where free it will still make no economic sense.

[DougSpindler]

What do you do if there are several overcast very cold days in row? 

[cdev]

I would parse the weather predictions several days in advance and set some variables so that energy usage was as minimal as possible to make whatever reserve I had last longer.

I worry about volcanic eruptions and the potential for diminished solar power as they can cause dramatic cooling periods that can last (in large cases) as long as several years or in some cases, even longer. Benjamin Franklin, one of the founders of the US and a pioneer in the firled of electricity wrote about the Icelandic ewruption and the extremely hard winter that followed it, ("The year without a Summer") Edvard Munch's "The Scream" depicts a red sky in northern Europe after the volcanic eruption at Krakatoa, many thousands of miles away and near the Equator.

During that "volcanic winter" time there is also much less rain and less wind. Its cold and dry. Historically eruption periods have caused large scale famines all around the world.

They happen randomly, so you can bet they will continue, even in the modern era. We have to be ready.

[coppice]

I wonder how many people have a climate where this would work?

I will say at least 90% of the world if not more has climate where this will not just work but also be more cost effective than any other source.
My location is relatively sunny (sort of average) and about as cold as it gets.

I think your 90% figure is very optimistic. I live in Yorkshire, UK, and I think our conditions are fairly typical of huge swathes of the kind of climate which require serious heating throughout the winter. Today is typical for this time of year. Cars have been using their headlights all day today, and for the past few days, as there has been 100% dense grey cloud cover. The output from PV would be close to zero. The average output of PV systems in the summer is not too bad, but during the winter 10kW of panels (I think you said that's what you have) will give an average of about 300W. The low number of daylight hours, and the large number of completely overcast days lead to that figure. There will be some periods of a couple of kilowatts, when the sky is sufficiently clear, which is when most of that average of 300W will be produced. However many panels you put in to boost output in the good times, you'd need a way to ride over multiple weeks of essentially zero output.

[electrodacus]

What do you do if there are several overcast very cold days in row?

The last 5 days where like that overcast not typical as it was quite dark and last night was a bit of a snow storm with today 6th day the first with some sun. The thermal storage is designed to deal with that that is why I need a 160kWh thermal storage currently just 97kWh installed.
When this long overcast stretch started I had about +25.5C and this morning there where only +18C that is a bit low but that is because I do not have quite enough thermal storage and will need to add that 61kWh soon.
Temperatures outside where fairly moderate an average around -2 or -3C for the past few days but last night got colder -10C and even today it stayed at a max of -9C but since it was sunny I had a bit of heat going back in to the thermal mass plus a lot of electric cooking so now it is +21.5C
The house losses are around 20kWh (with this mild temperatures when is colder is over 30kWh but then is also normally sunny) per day so a 160kWh thermal storage will be fairly decent even the 97kWh is sort of acceptable if you want to deal with +18C a few days a year but PV array also produces something typical around 4kWh from my array in a dark overcast day (that is will multiple cloud layers and you are not able to see the sun at all).
Next few days should be mainly sunny so thermal storage will get full again and 5 consecutive overcast days are not very common here this was around the worst case.
But the main idea is thermal storage should be sized to deal with worst case and it is so inexpensive that is not a problem to add as much thermal storage as needed.

[electrodacus]

I think your 90% figure is very optimistic. I live in Yorkshire, UK, and I think our conditions are fairly typical of huge swathes of the kind of climate which require serious heating throughout the winter. Today is typical for this time of year. Cars have been using their headlights all day today, and for the past few days, as there has been 100% dense grey cloud cover. The output from PV would be close to zero. The average output of PV systems in the summer is not too bad, but during the winter 10kW of panels (I think you said that's what you have) will give an average of about 300W. The low number of daylight hours, and the large number of completely overcast days lead to that figure. There will be some periods of a couple of kilowatts, when the sky is sufficiently clear, which is when most of that average of 300W will be produced. However many panels you put in to boost output in the good times, you'd need a way to ride over multiple weeks of essentially zero output.

You think 90% is optimistic because you happen to be in that 10%
A 10kW PV array will produce at your location about half compared to my location 8MWh in a year vs around 14MWh at my location but the bad part is of course in Winter months with worst case December just 252kWh and February 439kWh that is probably already fine.
Average temperature at your location is around +4.3C in December Link so assuming a target of +20C inside temperature that means just 15.7C delta.
Where average temperature at my location in December is -13.3C Link thus a delta of 33.3C so more than 2x colder thus 2x more energy for heating the same house.
I get more solar in December about 700kWh so if I need to extrapolate you will need about 30 to 40% more panels assuming you move my house at your location so I should increase the PV array to 14kW or so to deal with less sun for worst case month.
Still it will be the lowest cost heating option even at your location as natural gas is slightly more expensive than at my location still extremely subsidized as it is here and likely not to stay the same.
So less sunny places have usually milder climate. 

[cdev]

What do you do when a substantial number of days are overcast? Do weeks ever go by without any bright sunny days?

[electrodacus]

What do you do when a substantial number of days are overcast? Do weeks ever go by without any bright sunny days?

Check a replay that I just made earlier the thermal storage can deal with up to a week with no sun and thermal storage is cheap.  Same amount of thermal storage will work in your climate also as I'm sure you almost never see the sun in December based on the 252kWh generated in December.

Check page 7 in my presentation to see how the daily energy output from a 10kW PV array at my location looks like over a full year.

[cdev]

My friend who used to live in Amsterdam complained that days when it was overcast would result in miniscule electricity output from PV units even if it was quite bright outside otherwise. She said this was the dark dirty secret of solar setups in Holland. In other words they seem to be very non-linear as far as ability to generate electricity. They require direct sunlight (albeit at a low angle as you point out seems to be fine) to really function as they are meant to. The sunny days still may be enough for most places.

Like northern Europe, the Pacific Coast north of approximately Ft Bragg (Sonoma County) northward all through the Pacific Northwest here in the US, and British Columbia in Canada also have a *lot* of overcast days.  I dont know a good source for getting the number of cloudy vs sunny days for a specific area. Need to look for one.

I think the situation is more favorable where I live (East Coast of US) - probably comparable to parts of Germany and central Europe.

Its not as overcast here as Holland or the UK are.

One problem, we do have air pollution here, Not as much as thre used to be, but unlike California where the air was quite clean, there is always a bit of black grime thats carried by the rain, that collects on things.

[coppice]

My friend who used to live in Amsterdam complained that days when it was overcast would result in miniscule electricity output from PV units even if it was quite bright outside otherwise. She said this was the dark dirty secret of solar setups in Holland. In other words they seem to be very non-linear as far as ability to generate electricity. They require direct sunlight (albeit at a low angle as you point out seems to be fine) to really function as they are meant to.

Your eyes have irises. PV panels don't. Until things are quite dim your eyes compensate, and things don't seem all that dim, even though the insolation can be way down from that on a bright sunny day. Once your irises are fully open, any further drop in illumination becomes very obvious.

[DougSpindler]

My friend who used to live in Amsterdam complained that days when it was overcast would result in miniscule electricity output from PV units even if it was quite bright outside otherwise. She said this was the dark dirty secret of solar setups in Holland. In other words they seem to be very non-linear as far as ability to generate electricity. They require direct sunlight (albeit at a low angle as you point out seems to be fine) to really function as they are meant to. The sunny days still may be enough for most places.

Like northern Europe, the Pacific Coast north of approximately Ft Bragg (Sonoma County) northward all through the Pacific Northwest here in the US, and British Columbia in Canada also have a *lot* of overcast days.  I dont know a good source for getting the number of cloudy vs sunny days for a specific area. Need to look for one.

I think the situation is more favorable where I live (East Coast of US) - probably comparable to parts of Germany and central Europe.

Its not as overcast here as Holland or the UK are.

One problem, we do have air pollution here, Not as much as thre used to be, but unlike California where the air was quite clean, there is always a bit of black grime thats carried by the rain, that collects on things.

Hey don't think California is pollution free.  Thank you government officials from imposing strict emission controls on cars our air was nearly smog free.  That is until China started building coal fired power plants.  Now when we have smog days it's China's pollution that's causing it or forest fires.

 

[electrodacus]

My friend who used to live in Amsterdam complained that days when it was overcast would result in miniscule electricity output from PV units even if it was quite bright outside otherwise. She said this was the dark dirty secret of solar setups in Holland. In other words they seem to be very non-linear as far as ability to generate electricity. They require direct sunlight (albeit at a low angle as you point out seems to be fine) to really function as they are meant to. The sunny days still may be enough for most places.

Like northern Europe, the Pacific Coast north of approximately Ft Bragg (Sonoma County) northward all through the Pacific Northwest here in the US, and British Columbia in Canada also have a *lot* of overcast days.  I dont know a good source for getting the number of cloudy vs sunny days for a specific area. Need to look for one.

I think the situation is more favorable where I live (East Coast of US) - probably comparable to parts of Germany and central Europe.

Its not as overcast here as Holland or the UK are.

One problem, we do have air pollution here, Not as much as thre used to be, but unlike California where the air was quite clean, there is always a bit of black grime thats carried by the rain, that collects on things.

Here is a good resource for for solar energy generated in any place around the world https://pvwatts.nrel.gov/ you can even download hourly solar data for your location to have a very good ideal on what a PV array will produce.
I have linked to my pdf presentation in a comment above but I think is maybe better just to post the graph in here as you will get a very good idea of what is the minimum and max solar energy production for a 10kW PV array and even if that is for my location almost any location in US if not all will have similar or better solar output and for sure milder winters. On the x axis is the day of the year like 1 is January first and 365 is last day in December while on the y axis you get the energy output in Wh and as you see there are very few days with less than 10kWh output and worse overcast snowy day's are still at least 3 to 4kWh but those are not many in a year.

[DougSpindler]

Interesting the swings you have from near 6,000 to 1,000 back to 6,000 in just one day.  I suspect those are foggy and rainy days?

[coppice]

Interesting the swings you have from near 6,000 to 1,000 back to 6,000 in just one day.  I suspect those are foggy and rainy days?

What is interesting is that he never sees more than a few days of sustained low output. That's much more consistent than most locations.

[electrodacus]

What is interesting is that he never sees more than a few days of sustained low output. That's much more consistent than most locations.

Have you looked at the winter months especially November and December ? Around day 290 there are 6 consecutive cloudy days then similar around day 320 I will consider that fairly bad and the reason I need a relatively large thermal mass storage able to deal with about a week of reduced solar output.
If you look at the green doted line that represent the annual average at least 50% of the days are below meaning there are at least some clouds.
You can download hourly data from pvwatts website and create the same type of graph for your location as you may have a wrong impression about how data will look like. My graph is based on data from PVwatts for my location and used a spreedsheet type application to plot that graph that represents an average type of year based on more than 30 years of recorded data so fairly accurate representation and confirmed by my measurements over the past few years as fairly accurate.

[coppice]

What is interesting is that he never sees more than a few days of sustained low output. That's much more consistent than most locations.

Have you looked at the winter months especially November and December ? Around day 290 there are 6 consecutive cloudy days then similar around day 320 I will consider that fairly bad and the reason I need a relatively large thermal mass storage able to deal with about a week of reduced solar output.

For most people in a cold climate, 6 days is not a long lull in output.