PV panel water heater idea


Auckland, NZ
So I’m wondering if it’s possible to DIY a solar water heater on a PV panel so it’s dual purpose. We all know solar panels get hot so why not use that energy to heat a small tank in a camper van for warm showers and washing dishes.

This idea is probably commercially available but I haven’t seen it

can folks give me a bit input to fill in the gaps of what I know.

So I’m thinking of snaking a load of pipe across the back of a PV panel to transfer that heat into an Antifreeze liquid inside. That liquid would then transfer the heat into a small insulated hot water container enough for 2 showers

any ideas on the best kind of pipe to use for the back of the panel? I’m thinking it would be enclosed to help more efficient heat transfer. Is there any square or flat sided piping so a side can sit against the panel for more surface area

Any ideas on how to transfer the heat into the water in a small (15 litres, 4 gallons) tank?

What pressure release valves etc are needed in a system like this?

Any links to websites with info gratefully recieved.

If PV panels are 20%ish efficient and water heating tubes are 50%ish efficient what would the efficiency of a double duty DIY panel be?


🌞SW sunshine =⚡️⚡️lit up thru the darkness✌️
There is a thread already addressing this.

Fred S

Solar Addict
That thread is mostly about cooling the panels, rather than practically capturing and transferring the heat.
Systems that use piping (water/antifreeze) to transfer solar heat to a tank, or alternatively to use PV to electrically heat a tank, can be more complicated than it may seem at first glance. If you search you can find other threads in this forum on both approaches. For a camper van, a small propane water heater may be the most practical approach (the most [and fastest] btus into the water).


Photon Sorcerer
I'd be looking at a small heat exchanger tank rather than running the loop pressurised. There was a brand of water heater sold in Australia, Saxon, full copper everything with sizes all the way up to family size. The bath was indirectly heated with typically an electric element which slid into a cavity at the bottom of the bath. The pressure line to be heated from the water bath was a pretty generous coil so really good heat hold up when the water was flowing. They were dead easy to externally heat since you could place the external loop across the bottom drain plug and overflow. Quite popular in the what is now called off-grid community. Mine lasted about 40 years before the tank finally developed some pin holes. But for the nasty insulation it could have been easily fixed by soldering the holes up.

You never know @ianganderton there might be some of them still floating around NZ.

*edit due to flawed recollection*
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Off Grid Design and Installer
I think the technology has never taken off because its a bit complicated and doesn't "pencil" for residential and/or commercial applications. There are some companies making the product though.

Dual Sun


Solar Addict
Here is an idea on the next level:

Use those solar panels to collect (and filter) rain water by tilting them slightly and collect the water under the panel in order to heat it.