Passive Solar Water Heater





Introduction: Passive Solar Water Heater

I live in the north. I wanted a passive solar water heater that could warm water that could be used to warm soils for growing more productively. I was able to make this passive solar water heater that was efficient, low cost, low tech and fairly easy to make. This solar water heater was able to warm the water in the 45 gallon plastic barrel 15 degrees Celsius in about two hours.

Step 1: Materials

double wall polycarbonate sheet

1 ½ PVC pipe

2 end caps

2 reducer caps

5’ of ¾ poly pipe

2 barrel bungs for ¾ poly pipe\PVC solvent

4 1” pipe clamps

Silicon bath sealer

Flat black spray paint

45 gal plastic barrel

Step 2: The General Design

For the overall design, I used the double wall polycarbonate as the channel that water moved through. As it moved up the channels, the thin tubes of water are heated, creating a convection action. The water in the 45 gallon plastic barrel is filled to match the top of the polycarbonate panel. The back of the polycarbonate panel is painted flat black to increase heat absorption. The panel is angled at about 40 degrees from the horizontal and faces south to maximize the solar gain.

Step 3: Preparing the Barrel

The plastic 45 gallon barrel is fixed with two bungs positioned so one is even with the bottom of the solar panel and the other even with the top of the solar panel. Water will be filled above the level of the top bung. This will mean there is on difference in water pressure are even

Step 4: Preparing the Panel

The panel is made from double wall polycarbonate. This 1/4" material has channels that allow water to flow upward, moved by convection, from the bottom to the top of the barrel. The panel is heated by sunlight as it passes through the front of the panel but is absorbed by the black coating on the back of the panel. The water moves through the bottom and top PVC pipes that are fitted to the panel.

Step 5: The Top and Bottom Pipes Linking the Polycarbonate Panel

I cut two pieces of polycarbonate to lengths that were about 2” longer than the panel is wide. I then ripped a ¼ slot down one side of each of these pipes. Slide the panel down the slots in the PVC pipes. I then dry fit the end caps and reducer caps to the PVC pipe with the panel installed. This will then determine the length of the PVC pipes. Cut the pipes so that both ends fit snugly against the panel. Run a bead of silicon along the edge of polycarbonate so that it will seal the PVC pipe when it is pulled into the silicon bead. Once the panel is sealed with the PVC, the end sections are cemented in place and attached to the 1/2" poly tubing. The poly tubing is then attached to the bung fittings on the barrel.



    • Make it Move Contest

      Make it Move Contest
    • Pets Challenge

      Pets Challenge
    • Casting Contest

      Casting Contest

    We have a be nice policy.
    Please be positive and constructive.




    Excellent use of polycarbonate sheet. I have lots of these lying around and it has never occurred to me that It can be uses as a kind of piping. Nice.

    Good idea indeed! I made something similar with an old radiator, but this is much easier to expand. How about frost, any experience with that?

    Great idea, I have to try it! I have found some cheap plastic barrels at I will try to build a passive heater as well.

    It looks quite interesting...passion drives innovation.... Cheers..!

    1 reply

    Great idea. I would also paint the panel both sides. The black attracts the heat. I do worry about the BPA. I would like to build something like this to warm water for my fish dam. That mean that I will have to let the warm water flow into the water where the fish live.

    You might be able to improve your results by facing the black surface outward. I don't think there's any reason the sunlight has to pass through the water; it just needs to heat the polycarb panel. The shiny surface that you have facing the sun is probably reflecting a certain amount of light. You could also paint the PVC pipes and the barrel itself flat black; no reason to waste those surfaces. Great work!

    This is clever but not safe. Polycarbonate is full of BPA, which is an endocrine disruptor. If you use this to heat water, the massive surface area and added heat are likely to increase the leaching of BPA into the water. If it were not for this one fault of this design, I would approve of it.

    1 reply

    The water is used for greenhouse heat and watering. The BPA in the polycarbonate would not be ingested.

    This is a very clever idea. I'll be bookmarking this one.

    Excellent idea especially the use of the polycarbonate sheet

    Great idea! The sun is there, and we need to use it more creatively, as you have!