Water cooled panels

[Popuptoaster]

I have been thinking about experimenting with water cooling my solar panels by running coolant pipes behind the panels, I reckon if I can lower the temperature enough tto increase the panels efficiency to cover the "cost" of powering a pump then i'm getting free warmed water and it might even be possible to get a net gain over that from the panels.

I don't really have the space to add separate solar water heating so thought this might be a good compromise? I wondered if anyone had seen anything done along these lines? I have seen some commercial applications where they spray the panels with water and cool by evaporation but that strikes me as just being wasteful.

 

[Supervstech]

I have seen panls submerged in a cool water tank, increase output.
I would use a header with small 1/4-1/2" tubing flowing water to get as much heat transfer into the water.

 

[amaclach]

You could use convection to circulate...
Cool water in the bottom, as it warms up, it rises to the header tank at the top. As warm water is drawn from the header tank by use, new cool water is siphoned up into the system from the bottom. Of course, there should be a return from the bottom of the header tank to the bottom, so it can keep circulating. No pump needed!
I believe that this is how solar water heaters work.

 

[amaclach]

Ideally you'd have the cooling pipes soldered to the heat sink, which would be an aluminum or copper plate covering the back of the panel. The cooling (heating?) Pipes would also have to be Al or Cu

 

[Popuptoaster]

Yeah copper would be ideal but to costly for me I think, I like the idea of a convection system, it's one less thing to fail, but I live on a boat, not sure if her moving around might disturb the flow or not. I don't suppose it matters much, it's not like the cooling would be critical and a pump could be added if there are problems.

 

[Supervstech]

The problem with convection is the panels need to be the lowest point to keep them cool... shadows and such could pose issues this way.

 

[amaclach]

Yeah copper would be ideal but to costly for me I think, I like the idea of a convection system, it's one less thing to fail, but I live on a boat, not sure if her moving around might disturb the flow or not. I don't suppose it matters much, it's not like the cooling would be critical and a pump could be added if there are problems.

Al is almost as good and a LOT cheaper. Can also be easily brazed

 

[amaclach]

The problem with convection is the panels need to be the lowest point to keep them cool... shadows and such could pose issues this way.

Nah - just lower than the header tank.

 

[svetz]

I've seen those cheap misting systems on Amazon ... wonder how that would do hitting the back of the panel? Probably The $ cost vs. energy gain wouldn't be there for the super humid area I live in...

Let's assume -.37%/°C for Pmax and that it would give 10° cooling. So, for a 340W panel, that would be a 3.7% gain, or 12W gain. Wouldn't have to run around noon (why bother cooling when you're clipping?). A mister consumers ~1.5g gallons per nozzle per hour, so 25 heads would use 40 GPH. Let's say we run it for 5 hours/day, that's 200 gallons or about $1.00 worth of water. 25 panels at +12W for 5 hours = 1.5 kWh, or about $0.20. Here the water would just drip off, way to humid. But in Colorado it might evaporate, and 40 gph of evaporation would be 32 kBtu/h - probably more than 10°.

 

[ianganderton]

I’ve just been thinking about this. Weird!

I’m wondering if something like underfloor heating pipe could be used and glued to the back of the panel in a long loop then enclosed (maybe insulated)

small low wattage circulating water pump (don’t know what exactly) to move the coolant because on the roof of the van there isn’t room for a header

something like a 2 gallon 15litre well insulated hot water tank with heat transfer coils inside. Would this be possible to DIY?

don’t know enough yet about RV water systems but it must be possible to pressurise it from a pump for water to flow to a mixer tap

what safety valves would be needed?

 

[ianganderton]

https://www.builditsolar.com/Projects/WaterHeating/MSClosedLoop.pdf

 

[ianganderton]

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12V 5W by the looks of it. Connected via a relay to only run when there is sun on the panels

 

[tictag]

There must be combo-PV/thermal panels out there, you're not telling me nobody has thought of this or that there isn't a commercial demand for such a system? I think it would be a really cool idea (pun intended) to get both electricity and hot water from such a combo panel.

 

[Popuptoaster]

I think a pumped system without a header tank would probably be best for my boat, easier to get working and easier to control the speed of flow, less weight and gubbins up on the roof and I have 24v power so a pump that can lift the water high enough should be easy enough to source and i can run it via a temp sensor so it only pumps coolant when it's worth while.

 

[Popuptoaster]

There must be combo-PV/thermal panels out there, you're not telling me nobody has thought of this or that there isn't a commercial demand for such a system? I think it would be a really cool idea (pun intended) to get both electricity and hot water from such a combo panel.

I did Google, saw some water heating tube type that have PV panels incorporated, I suspect that most people who want both have the space for seperate systems and maybe boat people haven't really thought that much about the possibility as many of them will just start the engine or genset when they have a high demand application such as water heating running.

 

[Fred S]

When designing, if you want to insulate behind the panels you'll want have a backup for coolant circulation, so that a pump failure won't cause the panels to overheat. The convection cooling that normally occurs under the panels would be blocked. Don't know if this would cause damage - it may be worth some homework.

 

[Popuptoaster]

When designing, if you want to insulate behind the panels you'll want have a backup for coolant circulation, so that a pump failure won't cause the panels to overheat. The convection cooling that normally occurs under the panels would be blocked. Don't know if this would cause damage - it may be worth some homework.

I had thought about this, my plan is to fit a plate to the back of the panels with pipes running across the plate but with no insulation on the pipes until they go down into the boat interior, that way in the event of a cooling failure the panels will still be OK. This is only a bit of help for an existing water heating solution so it doesn not have to be super efficient, I'm just trying to capture some wasted heat.

 

[Fred S]

That should be fine. Have fun experimenting!

 

[Popuptoaster]

 

[Popuptoaster]

Well, just goes to show how weird the world can be, found that video couple of days ago then today another boat owner asked if I wanted some free solar panels as he wanted to get flexible ones he could walk on to make more deck space on the boat he's just bought. I thought it was odd when he said he'd rather give them to me than have to carry them up off the dock as they were heavy but turns out he wasn't wrong, they ARE really heavy, have water cooling/heating backing on them!