DIY Solar panel cooling water heater no power or fuel wasted!


New Member
So I see all kinds of videos about diy pool heaters that are just a coil of tubing put inside a frame (usually topped with glass) that is either lined with reflectix or painted black to absorb heat. After pumping water through it they seem to get a decent amount of heat fairly quickly.

My question is, could we use the back of our solar panels to essentially do the same thing?

I saw a video of a professional pool heating company that more or less did it to some movie actor's house (I forget his name, I'm not good at remembering actors..) with pool heating panels. His roof was full of pv solar, so they ran traditional solar pool heating panels along the back of them. The owner said they heated his pool to swim comfortably even in November and he got better efficiency out of his pv panels because of the cooling effect the water had.

My thinking would be to run the pax in a coil along the back of the panels and hold it in place with some strong chicken wire or something similar attached along all sides of the panel so the hose doesn't go anywhere and the panels still get some air flow to help with cooling. Even one panel would be enough to work okay I imagine, but I suppose the more area you have the faster you can heat your water. Running it in one continuous loop from one panel to the next then back down to an insulated tank. A great idea I saw for this was to use an old ice chest to store the water. It's inexpensive, water tight, insulated, and already has a drain built in. Simply seal the lid with silicone (or don't) and you're good to go. Adding in a temp controller like this one: will allow you to shut off the circulation pump when the water gets to a certain temp. You can also optimize it by adding a small 12v heating element that will heat your water the last bit if the solar maxes out at a temp lower than you'd prefer. You could use another one of those same sensors since you can program the min and max temp that it supplies voltage. You can also use the element as a power dump for excess solar generated when you batteries are full to get hot water faster.

Just an idea for pulling even more energy out of the same amount of space. It costs either a lot of power or a lot of fuel to heat water and I want to be able to stay in one place for a long period of time when the desire strikes, which is exactly why I'm going entirely solar/electric, so the only remaining limiting factor is food. So having to waste gas running my engine just to warm up a coolant heat exchanger or charge my batteries because too much power was drained by a heating element is less than optimal. Also, the thermal mass may not be exactly a ton, and correct me if I'm wrong, but the water would essentially be absorbing heat that would otherwise be going into the roof of your rig as well as pulling it off of the solar panels, so I wouldn't be surprised if it caused a very slight overall cooling effect inside. It would entirely depend on how much space was covered by panels + tubing, of course. I don't see any way this could harm your panels because the water wouldn't get any hotter than the panels, and in some cases would be cooling them, so in fact has the possibility of making them las longer.

Plate heat exchangers sound tempting, quick hot water, but only after your engine heats up, which alone takes a few minutes, and it would give my engine one more place to fail, which is usually the last thing I want, especially from my cooling system because that leads to overheating and in turn major damage. Going solar has about the same cost, 600 ft of pex pipe (which you probably won't use all of) is about the same price as a plate heat exchanger and both systems would use the same circulation pump. Also, all that pipe is discreetly expanding the capacity of your hot water tank! Airflow while driving may actually end up cooling your water now that I'm thinking about it, so perhaps a plate exchanger wouldn't be a bad addition as well, use the same pump with a t ball valve to control where the water goes. A 3 way water heating system that doesn't use any extra power draw or fuel! Unless you want it to...

I see companies are starting to talk about this, combining solar water heating and power generation, both have been around individually forever now, so why does it seem taboo? What do you guys think? It would add weight to your panels so you would probably need to strengthen the mounting brackets. Also, depending where you live or plan on traveling to, freezing could be a concern. However, I've seen solar water heating work with snow on the ground, so maybe just keep the flow on constant to ensure it doesn't freeze, and supplement those situations by running the element a little more if necessary.

Anyway, thoughts and opinions please, I'm really curious if anyone has tried solar water heating in a mobile setup (other than the roof mounted tube tanks) and if anyone thinks it would work, or would there be too much gap/not enough contact, and other limiting factors that would make it take too long, be inefficient, or just a pointless waste of time. Don't hold back, tell me how it is. Cheers.


Solar Enthusiast
Maybe a pre heater for a water heater would be better then trying to heat 40 degree water out of your well


Solar Enthusiast
I have a 4 by 10 foot (40 sq ft) purpose built solar water heater panel on my roof and it heats 50 gallons of water very well, but I'm sure it wouldn't make a dent with a 50,000 gallon swimming pool - You'd need lots of square feet if your panels were efficient at heating water and tons of square feet with home made inefficient panels



New Member
Yeah, that's why I mentioned adding the 12v heating element, but still, all that temp change for the minimal voltage of the pump is much better than doing it all with a 300w heating element. Most of the time I think the solar might be enough though, just turning on the power when you want to take an extra hot shower with it, or you need hot water when its cold and overcast.

As far as using it for a pool, I'm not sure why that's their stated use for it, my best guess is because it doesn't over heat the water, but would be a perfect cool/warm pool temp... eventually... If you ran it 24/7 it might do an ok job, but


Solar Enthusiast
YamInaBox: I encourage you to look into solar hot water heating. It works very well, and is not terribly difficult. Instead of responding to your many points, I will make the general comment that many of your assumptions are not accurate. I suggest you read up for an hour or two or three on the "Build it Solar' website. You will learn a lot, and then will be able to reach better informed conclusions.

By the way, 600' of PEX is a lot of PEX. The site I've suggested has many documented cases and they have data. So you can actually look at the results for a copper collector versus a PEX one, just as an example.

Happy reading...