Wanting to get into solar? Think HOT WATER

[Lightages]

I live in the middle of nowhere in the desert and have a gravity hot water system with a non-pressurized solar hot water system. It gets down to -15C at night in the winter. My system is a 200L tank with double wall glass tubes with a vacuum that heat the water. I have to keep the water trickling when the temp gets below zero to keep things from freezing in the pipes to the house but that is because I haven't taken the steps to keep it from freezing in the pipes. The tank and tubes have no problem with below freezing. I have enough water for two people with this system. The systems cost me $500 plus plumbing. Hard to beat that for cost!

So it depends on what you expect and/or need from a system. There is no way I could do a proper hot water heating system with PV energy for under $4000 here. I just happen to have a 3kW soar system with a big battery bank that is charge before 2pm so yes I could also heat water with an electric heater but my system cost much more than $10000.

[tron9000]

http://www.immersun.co.uk/

I saw these guys at New Electronics last month. I know its UK based, but its a system where energy its can't dump into your gird, it dumps into an immersion heater.

They did let us take the top of one of their units and poke around though!

Rather than hot water: guy i work with had seen an idea where the energy not used powers a compressor and stores it as compressed air...then use the compressed air to run a turbine generator, as and when.

[m100]

I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste,  ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age.  Even in the UK it worked, but then again we had endless summers decades ago.

I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W.  Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.

If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel.  Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.   

Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)

[Kleinstein]

Compressed air is a rather low efficiency way of storing energy. Normal compressors and air powered tools combined give about 10% efficiency. With a better turbine you might end at 2-3 times that, still far from efficient. Batteries are much more efficient.

Having PV to supply electricity as a main function and only spend excess energy to make hot water is a different thing. Then on usually already makes 50/60 Hz AC from it. So one can use standard AC water heaters as well, and PV voltage is more in the 600 V range.
Having a local isolated grid just for your home is a rare case.
Depending on how much you get paid for electricity this might be economic, though rates are subject to change. At least in much of Europe this may mean you save a little in summer, but have an expensive way of making hot water for the rest of the year, when the sun is not enough. You also might need a sizable buffer, as there will not be excess electricity every day or even every week.

[Seekonk]

It is a common misconception that panel voltage varies with light intensity. Panels are a current source. The power point voltage of a panel for all practical purposes only varies with temperature.  Tracking panel temperature is an effective way of creating a MPPT controller.  Even having a fixed power point is effective enough if adjustment is made by season.

I just finished a test in May with a single 100W  solar panel connected to my water heater. This is at location 39N latitude and should be fairly typical for many people.  For a 23 day period, the average power created per day was 252WH.  Lowest daily power was 126WH and the highest was 413WH. An interesting aspect of temperature was evident.  Highest power create3d was 88.6W on a day with only 162WH
created for the day.  Clouds kept the panel cool till that burst of sunshine came through.  On the best day, 413WH was created but 57.7W was the maximum power.  This is the reason "12V" panels have a 18V power point at 25C.  A temperature they will only see in winter. 1KWH is a good estimate for 400W of panels.

Life isn't always simple. At my camp none of my solar panels are actually on my property.  It can be difficult to find a place close to put solar, adding plumbing makes it even harder. Antifreeze, heat exchangers and pumps add a lot of cost. Throwing a couple hundred feet of garden hose on the roof isn't a solution. I don't think the title of the thread should change.

It is a simple idea. If electric is used to heat water, replace some of that with solar PV. Hardware wise this is a minimal solution if you only have a few hundred to spend. If you don't use a power point controlling solution, half the power will be wasted.

This is the same technology used in linear current boosting for remote pumping systems without batteries.  You would think someone in the entire world would have some question about hardware or software.  To paraphrase a famous astrophysicist when asked what aliens from another planet would think of us.  They would think of us as chickens, something to eat.

[rx8pilot]

I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste,  ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age.  Even in the UK it worked, but then again we had endless summers decades ago.

I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W.  Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.

If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel.  Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.   

Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)

Same.

[m100]

Compressed air is a rather low efficiency way of storing energy.

Regardless of that they are now being installed for UPS/standby power installations in electricity substations in the UK, replacing 48v and 110v battery banks.   Large capacity external compressors are already used on site for the switchgear. 

http://www.flowbattery.co.uk/case-studies/national-grid-case-study

[VK5RC]

Isn't that compressed air just to run the sub station,  it is 24kWhrs total,  also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo'  across the room having had its regulator accidentally knocked off.  Maintenance would be significant,  rust on the inside is a significant issue in the long term.

[rx8pilot]

Isn't that compressed air just to run the sub station,  it is 24kWhrs total,  also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo'  across the room having had its regulator accidentally knocked off.  Maintenance would be significant,  rust on the inside is a significant issue in the long term.

I am not specifically familiar with that system. In general, the cylinders have a large margin of safety, safety valves, and they are all tied together. The compressors filter and dry the air so that water does not end up in the tank. Common practice for life supporting systems like SCUBA. Industrial cylinders have a very long maintenance free life. They are supposed to be tested periodically, but not as often as 3000psi SCUBA tanks.

I would totally believe that the maintenance would be low when used as standby only. It only appears to backup the logic of the operation. It is a LOT of bulk to make that much power. A traditional generator and on-site propane tank would be my choice.

[Someone]

I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste,  ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age.  Even in the UK it worked, but then again we had endless summers decades ago.

I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W.  Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.

If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel.  Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.   

Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)

You get there in the end, its about the specific economic situation that most residential solar installations are in. Also note that installing an electricity storage system (battery, flywheel, etc) is both expensive and usually requires permits/licensing which storage as heat in hot water gets around.

[eas]

Installing PV solar just for hot water doesn't make much sense to me. Installing PV solar for hot water as a stepping stone to something else might make sense to me, but my first panels before I do a real installation are probably going to power my servers and network gear and a battery backup.

Using excess power from a PV installation to heat hot water makes perfect sense to me, particularly given how cheap panels are these days. If you are already grid tied, and have the space, it seems like the simplest thing would just be adding an extra electric tank water heater upstream of your existing water heater and powering that with the excess power.

I was thinking it might be fun to use excess power to refine aluminum, but that isn't too amenable to intermittent power. I guess there is always electrolysis.

[m100]

Isn't that compressed air just to run the sub station,  it is 24kWhrs total,  also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo'  across the room having had its regulator accidentally knocked off.  Maintenance would be significant,  rust on the inside is a significant issue in the long term.

The compressed air primarily has just operated the switchgear, and normally there would be a pair of 48v and 110v lead acid batteries for protection, tripping and SCADA equipment.   It's replacing, at least for  now, one of the pair of batteries.   The compressed air needs to be of a high quality in terms of moisture and oil for the switchgear (it's the insulant as well as one of the means of extinguishing the arc)  so it's already put through dessicant stacks and refrigerant driers.  The claim is a 40 year asset life, there are fixed air receivers older than that right across the UK that are still servicable and insurable.

[madires]

We got a few solar panels for hot water and supporting the central heating (oil) and it really helps to reduce the oil consumption. Based on the sunshine the central heating runs from autumn to late spring only. The hot water is stored in a split tank (hot water and heating) of about 1000l. I think, in the summer the system could provide hot water for two or three houses easily, just would require some piping to the neighbours and more tanks

[Kleinstein]

Compressed air directly from the compressor contains quite some water, unless you live in a very dry dessert environment. If you don't want the water, this needs an extra dryer with extra costs, energy consumption and maintenance. If you just want hot water, the compressor still might work, as for 1 kW in, you get slightly more than 1 kW of heat and the compressed air in addition.

There are a few tests using large scale compressed air to store excess energy (e.g. solar or wind), but usually they don't use the air to directly drive a turbine, but to combine it with natural gas, to get something like a gas turbine with decoupled air compression. So the compressed air is used to get a very high efficiency gas turbine when needed. Something like half (or more) of the energy still comes from the burned gas. Even with this trick efficiency is not that great.

[eneuro]

Creating hot water is the most effective way to use a couple of PV solar panels since close to 100% of the power generated will be used.

Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI http://en.wikipedia.org/wiki/Solar_thermal_energy, so you need store solar energy directly as a heat without any conversions to battery, etc


So, you might need 3m parabolic mirror ot create decent CSP system and using additional sun tracker software position dish directly into the sun and have w few kW of thermal energy stored as a heat ready to use with high efficiency

Future is now - 500 suns concentrated in vacum insulated absorber at 3m parabolic dish focus


This is free energy, look at those numbers in this video below description:
The new 15ft (4.5m) diameter SolarBeam is capable of providing 13kW (44,000 btu's) of thermal heat per hour. Unlike solar flat plate panels or evacuated tubes that lose efficiency with higher operating temperatures, the SolarBeam maintains a continuous 82% efficiency.



There are also other patents like this below-I like beter this idea of mounting such huge dish (10m), but its Fresnel lens probably costs a lot so much lower ROI than in the case of classic parabolic mirror, I guess 


Now you see, why I'm interested in 3m dish-because do not need so much power, but could easy cut mirrors into 5m diameter parabolic dish  if wanted more

-----
SUN is: 2015-06-3.897 21:30:59 UTC (2457177.397 JD)  lat: 50.***N  lon: -20.***E  Sun hour azimuth: -14.876  Sun (geo) azimuth: 194.876  Sun elevation: -16.230  Sun CSP power: 0.0 W  Day of the year: 154

[mtdoc]

Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI

PV efficiency is essentially irrelevant unless you are going to argue that sunlight is a limiting resource. PV efficiency only comes into play if you have a very  limited area to place panels.

Efficiency of converting the power produced by PV into heat is a different issue and is not "very low", in fact depending on how you use that electricity to heat water it can be very good.

As I stated earlier, direct solar hot water heating is often the right solution but not always. Using PV to heat water can be both efficient and economically rational in some cases.

[tron9000]

There are also other patents like this below-I like beter this idea of mounting such huge dish (10m), but its Fresnel lens probably costs a lot so much lower ROI than in the case of classic parabolic mirror, I guess 

  Jesus that's the biggest lenses I've seen! bet that's a bugger to clean, or worse, replace!

[Seekonk]

In my first post I said I didn't want to discuss the economics or direct solar heating. There were certainly enough technical issues to discuss.  Some have reasons other than economic for going into solar.  In a prior post my experiments indicated 400W of solar would produce on average 1KWH a day. That investment of $500 would yield about 8% ROI with moderate electric rates and no government rebates.

The government energy star website indicates that an 11CF refrigerator uses 920WH a day.  This is comparable with my water heating example. One person who is trying to save the world  www.solar-trap.com  proposes operating your refrigerator with solar.  This solution requires solar panels, charge controller, batteries, inverter, and
of course his custom board.  I estimate the total outlay for this would be about $2,500 and the batteries would likely have to be replaced in six years.  Small scale water heating is appealing for low cost and minimal hardware for the same KWH savings.  As I am moving in four days, I don't have the time for further discussions.

[tszaboo]

Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI

PV efficiency is essentially irrelevant unless you are going to argue that sunlight is a limiting resource. PV efficiency only comes into play if you have a very  limited area to place panels.

Efficiency of converting the power produced by PV into heat is a different issue and is not "very low", in fact depending on how you use that electricity to heat water it can be very good.

As I stated earlier, direct solar hot water heating is often the right solution but not always. Using PV to heat water can be both efficient and economically rational in some cases.

Completely agree. Unless you only have access to very limited roof, this is a very good argument in the PV water heater. Making a small scale water heating system looks like is not economic anymore, and as the OP revealed, the heating system can be stripped down to the very basics, reaching higher efficiency than generating a mains electricity, lower cost and and overall more flexible system. It takes a certain size where a system is viable and by the looks of it, cheap PV is the best for small scale. Thank for sharing this, I can only hope others will understand that efficiency is not everything.

[Kleinstein]

If you use the electricity only to directly heat water, you can not compare the value to electricity rates. There are often cheaper sources of heat than direct electricity to a tank. Even if you use electricity this may be a only on demand system, so you have less loss. Anyway the buffer can be smaller in an electric system.

With very small systems the PV way may still be cheaper than direct thermal, as the wire is cheaper and easier to route than tubings. But due to lower efficiency you need something like 2-5 times the area.

[eneuro]

Jesus that's the biggest lenses I've seen! bet that's a bugger to clean, or worse, replace!

While polution might be obvious issue with such thermal solar CSP system, I've optomized my parabolic mirror dish to be able cover mirrors side and this way protect mirrors and let clean everything just using high presure water karcher.

Additionaly, its shape reminds everybody who see this first time... UFO on house roof, while 3m dish focus is choosen to have the same height from diameter circle center to bottom mirror and to vacum absorber-simple math and solving equation for parabola parameter A, whereL y=A*X^2, allows us find this perfect focus, which for 3m dish is ~1.1m 
This way even strong wind will create very small aerodynamic drag when we move our dish in horizontal position, so no worry about flying roofs 

BTW: Putting many square meters of solar PV pannels at 15%max efficiency is like those solar roads  with hopeless ROI, additionaly  overall it destroys roof architecture design since those black PV pannels looks bad on nice red roofs, so I prefere to have 3m in diameter and 1m high UFO thermal solar and let neighbours and pedestrian guess what it might be 

[Poe]

BTW: Putting many square meters of solar PV pannels at 15%max efficiency is like those solar roads  with hopeless ROI..

I think that's backwards.

No offense intended, but I think you and many others are misunderstanding Seekonk's concept and/or goals.  (maybe I am?)

PV panels might not be as efficient as thermal systems, but that's not the point. 

The goal isn't to power your house from hot water or maximize power output from a given area of land.  Motives are purely financial.  i.e. To find the best cost per watt solution, to hasten ROI and minimize initial capital investment that could be making money itself.

His apparent intention is to minimize cost per watt by eliminating the most expensive parts.. the inverter, grid tie solution, batteries and professional labor. 

He is not suggesting a traditional PV install, but a much much cheaper version with the same panels.  He is suggesting a system with a ROI measured in months, not years like a traditional PV installation or a TES.

It is also scalable from a smaller size, unlike thermal systems and traditional PV installations. 

The initial investment would be one or two orders of magnitude less than those thermal systems you linked!

ALTHOUGH, I will say that this concept is only as scalable as the home's demand for hot water.  Beyond that, it falls apart.  .... unless you have another need for a poorly regulated intermittent power source.

[Seekonk]

That is a pretty good summation.  For the rest........

I can't believe it. You're trying to convince me to take the ugliest girl in town to the dance. You don't see it because she is your sister and all you can say is she is smart and has a good personality. I didn't take the prettiest girl, but she was easy.

If my neighbor told me he was installing direct solar I would tell him he is totally out of his mind. In some scale applications and climates it works.  For the majority it doesn't work. Do any of you heat water with it?  I didn't think so. In theory you focus on a small slice of the technology pie and ignore the rest of the system. One home program quoted $10,000 for a system.  I've seen these home built systems on roofs and a few years later they are gone.  I worked with a guy that had one.  A few years later he couldn't keep it from leaking.

You are correct, my post promotes a small system.  It only works if it is kept small and everything produced can be put into heating.  The voltage remains low keeping it under the radar of many building codes.  It can't produce that much heat so no plumbing is needed to install a tempering valve. Only a few panels are needed, enough to cover a garden shed. A system that is actually useful. A couple panels,
small controller and some wire.  It could be put in a box and sold at Home Depot as a weekend project. It is like the brick they came around with to put in the toilet to reduce water consumption. With tens of thousands of homes doing it it makes a big difference.  Two panels on every house would be a lot of energy.

This thread wasn't to encourage people to go out and buy panels.  There are plenty of people who want to buy them just to play with solar.  Just like all those who have a $1,000 digital scope who have no reason for more than an old Heathkit.  I thought it would be a venue to discuss importance of operating panels at power point, power point tracking methods and circuit designs.  So far it has been a waste of bandwidth with nothing but senseless dribble.  I think we need a delete thread button.

[vk6zgo]

If you use the electricity only to directly heat water, you can not compare the value to electricity rates. There are often cheaper sources of heat than direct electricity to a tank. Even if you use electricity this may be a only on demand system, so you have less loss. Anyway the buffer can be smaller in an electric system.

With very small systems the PV way may still be cheaper than direct thermal, as the wire is cheaper and easier to route than tubings. But due to lower efficiency you need something like 2-5 times the area.

Due to their higher conversion efficiency,the direct solar hot water systems common in Australia have a very much smaller footprint than Solar panels for Electricity generation of similar capacity.
Boosters are useful on Solar HWS,but not essential in places with a reasonable amount of sunshine.

The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.

[Poe]

The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.

The system proposed by the OP uses your existing electric hot water tank, adds a couple solar panels, some wire and a cheap circuit board.  It's as simple as mounting a couple solar panels to the shed with some 2x4 treated lumber, running a wire and having a cool beverage.

The system proposed by the OP..
- Does not add pipes, tanks, PTC valves, check valves, directional control valves, elaborate insulation, closed loop 'refrigerants', mixing valves, expansion tanks, heat exchangers, pumps, electronic controllers, temp sensors or even a single additional joint. 
- It does not use an inverter, grid tie solution, or batteries.
- There are no massive temperature fluctuations in the pipes/fittings causing expansion/contraction stresses.
- There is no worry of extra cold days causing freeze induced leaks, excessively hot days causing scaling, vapor lock, absorber fade, etc.
- There is no worry of equipment failure causing massive water/refrigerant leaking damage.
- There's no need to replace glazing, or refrigerants, recaulk seals, de-scale/drain the lines, or inspect for corrosion.

Maintenance of the OP's proposed system amounts to keeping snow off the panel. 

Actually, in the spirit of this concept, you shouldn't even do that.. because it would unnecessarily push out the ROI.