Solar waterer fail

Finished my solar-heated winter watering system the other day and was so excited to see if it worked! I set it outside just before a couple of 30* nights.

Not too bad looking for being made out of scraps, eh?


To test it, I put two identical buckets outside at the same time. Each had two gallons of water and both started at 63*. One was tucked inside the solar heater, the other set outside exposed.

By mid-morning the temp outside had reached 41* and was rainy when I checked on them. The one inside the solar heater was at 55*. Ok, but the other was surely at 41, right? Nope… at 52*, a mere 3* difference.

But water’s a great heat sink, so… maybe I just needed to give the buckets more time to differentiate? Or maybe it was too overcast to really heat up the solar water.


The next morning was clear and 45* after a night in the 30s. The exposed bucket was at 44*, and the solar bucket? … a disappointing 49*. 5* difference? That’s it? And the same the next time I checked as well. A puny 5* sure ain’t gonna keep the water from freezing when the daytime high is 20*!

Well, crap. They can’t all work out, I guess.

I still think the idea of a solar water heater is solid in theory though, and worth seeing if I can rework it. Some ideas:

  • replacing the wood panel in the front with glass (somehow), to remove the shadow on the bucket. No idea how I’d do this and keep it structurally sound. Maybe I can just cut a window in the wood panel instead of remove it completely?
  • Maybe there needs to be something inside that can suck up more heat and release it slowly at night to help out the water – like a thick sheet of metal painted black. Or something.
  • Maybe I need to think more along the lines of a solar cooker instead of the dehydrator that was my inspiration (in a dehydrator the food ought not be exposed to sunlight). I notice that in solar cookers, there are huge slanted reflective panels to direct the sunlight directly at the target. Like the one below, retailing for a cool $99 from

I notice on solar cooker design boards that people often use simple aluminum foil to get the reflections, so it won’t cost much to try.

Failures just teach us more, right? (Actually I’m not all that disappointed – I’m kind of excited to fool around with it more and see if I can make it better.)

Any more ideas? Leave me a comment, lemme know!

4 Responses to “Solar waterer fail”

  1. Ayse Says:

    A metal plate won’t work. You want something with thermal mass, not something very conductive. The water container isn’t heating up that much because it contains a lot of thermal mass, so it’s hard to move its temperature in one direction or another. That thermal mass may keep it from freezing, too.

  2. Diana Guillermo Says:

    Hi Ayse! Long time no see! I agree it needs more thermal mass, but it’ll take me a bit more thought to figure out how to accomplish that. Maybe I’ll have a brilliant flash of insight as I’m putting together the reflective panels.

  3. Ayse Says:

    Heh, I follow you by RSS so it’s like a whole extra step to comment. :)

    You could consider something like a row of plastic or glass tubes full of water with a dark reflective surface behind them, facing into the sun. That’s your classic solar water heater.

  4. Diana Guillermo Says:

    Aaaaaah. I think the “reflective” part might be my problem right now – I painted the foam insulation directly. No way it’s bouncing heat back onto the bucket. I made a cardboard/aluminum foil reflector and I’ll try that – think it’d be worth painting it black?

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