Solar for direct water heating

cptdondo Solar Expert Posts: 103 ✭✭✭
I have a small travel trailer with a 10 gallon water heater that runs on propane.  I will be spending a fair amount of time in the high desert (think lots of sun) in a remote area (think expensive to get propane) so I am thinking of ways to get free hot water.

My current thought is to get a couple of AC condenser coils, spray paint them black, put them on the roof and recirculate water through them.  I can get a solar pump and a simple dual thermostat controller on amazon.  

I’m thinking of coming off the hot side of the water heater, pumping up into the coils on the roof, and back to the cold side.

I’d have to have a way to drain it to prevent it from freezing and all that but that’s a couple of valves.

In general, does anyone see anything particularly wrong/right about this?

I’d love to find a potable rated solar collector but they don’t seem to exist in the small sizes I need.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,476 admin
    I would think that leaving the "fins" as manufactured, that you would have less than ideal harvest... I would guess you would put them in a glass surfaced box? You would not want any air circulation cooling the coils.

    If you have an extra coil to try, you might try flattening the fins in to a "plate" form.

    One of our "retired" posters here liked these solar thermal panels:

    These folks have lots of Solar DIY projects... Perhaps the collector for this one could be scaled down for you:

    Regarding the connection to the water heater. Generally, you pull water from the "bottom"/Cold side of the heater, and pump the heated water into the top of the water heater.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cptdondo
    cptdondo Solar Expert Posts: 103 ✭✭✭
    For an insulated box for the heat collector, what sort of bottom material should I use? I'm assuming it should be insulated so what would hold up to the heat?