DIY Solar Collector Boost Your Hot Water System

This home is heated by a wood stove in the winter, which also produces hot water. But the other three seasons it’s an electric water heater that does the work. This latest hack is a solar collector meant to take over the hot water production work for the house. it uses basic building materials and rudimentary construction skills, making it much more approachable than trying to make electricity from the sun.

It’s really just a wood box with a glass lid. The inside has been painted black, and the black tubing that snakes through it holds the water. A three-way valve lets the homeowner patch into the hot water reservoir. The collector is lower than the reservoir, so the heated water makes its way back into the tank as cooler water takes its place. Not bad for an entirely passive system!

[Thanks Minde]

23 thoughts on “DIY Solar Collector Boost Your Hot Water System

    1. The problem with heat from solar is usually that it gets to hot, leading to leakage and cracks. At least when you the cheapest way and try to get as much heat as possible. But swimming pools are very simple to heat with solar power; just add 100 meter of black irrigation tubing after the sand filter pump, and hey presto you have a heater.

      1. Evacuated tube (heat pipe) solar water heaters fix this problem passively. Once the temperature in the heat pipe gets too high, the fluid stops condensing and the heat pipe effectively stops conducting heat to the water pipe.

  1. At the website he mentions: “Anyway solar panels require direct Sun which in some regions does not appear very often.”

    Well this is not quite true with amorphous PV cells.

    1. It is true enough, that for every hour of difference in angle from dead center along either axis, you lose about 10% of your power, and the effect cumulates when both are offset.

  2. It’s a start. Lots of people start from scratch while there are lots of good books on the topic… hit the library before you build!

    Those supply and return lines need to be run indoors at the very least, and insulated or performance will be very low if not negative (hot tank water comes back cooler due to massive losses). The serpentine needs more coils. With thermosiphon, a manifold would be better (less resistance).

    No check valves to avoid reversal of the siphon which can cost you far more than you saved as your collector becomes a radiator at night. Admittedly not a big issue with this collector far below the tank.

    Still this guy will probably get some results and maybe it will lead him to a better system in the future.

  3. My grandfather built something like this back in the eighties, only larger. It was probably 8 feet by 5 feet and sat on the side lawn. It was a large wooden box painted black inside and the pipe came out of the basement of the house into the side of the box and ran back and forth inside the box and then came back out and back into the basement. The glass over the top of the box was a bunch of old window panes my uncles hauled home from the dump and/or had laying around. (They lived on a farm.) This was in southern Wisconsin and seemed to work quite well late spring through early fall.

  4. There are thousands of designs for this on the internet dating back to the 50’s.

    I suggest reading those instead of following this system that has some serious problems with it.

    It’s a good start, but it’s not a useable form. It’s more of a early alpha test.

  5. large bore tubing better for maximising flow rates with low thermal/density gradients

    check valve, as discussed, important for avoiding reverse thermosiphon at night if tank not much higher than panel

    insulation critical for reducing radiant and conducted losses

    angle of collector should approximate latitude to improve year round efficiency

    a simple microcontroller and one wire device monitoring temperature of tank and panel and a pump can improve efficieny of collection if the tank is close to the same level as the collector, as well as circulating fluid to the panel if it gets close to 4 degrees C, risking freezing and pipe rupture

    stagnation and high panel temperatures with long serpentine pipe paths have to be weighed against less radiant heat loss and more efficient collection of lower temperature water at higher flow rates

    this was all figured out in the seventies, then oil got cheap again, and now we need to re-learn it

    1. Plexiglass will craze after a while, ironically it’s the ultraviolet light that does it.

      There’s bugger all UV in sunlight anyway, it’s about 50% visible light, 50% infra-red and the rest is UV. (Ok, UV is ~10%.)

      The main problem is glass blocks infra-red, so there goes about half of your energy. The fix is to use quartz glass, that passes visible, IR & UV – score! A bit pricey though.

      1. Low iron content plate glass (less green looking) is often used as it allows more energy to pass through.

        But, it is expensive, and the difference is only in the single or low two digit percents, and in this application if second hand plate glass can be obtained and used cheaply, just make the thing a few percent bigger to compensate.

  6. score! this’ll be a perfect project for me! My hot water system relies on a solid fuel fire stove or clicking on an immersion heater, which chews power.

    When I need hot water for washing up, I have to turn the kettle on, otherwise I have to wait half an hour for the water to heat up.

    Now british summer time is here I can build one of these for the flat roof on the side of my house!

  7. I bought some hollow vacuum tubes meant for use in commercial solar hot water heaters, and I have NO problem getting my water up to 100 deg C, I actually use it to make tea.

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