Our passive greenhouse solar water heater

It can’t get much simpler:

An old window framed with old 2 x 4s, an old piece of OSB for the backing, 20′ of 3/8 cooper, 3/8 and 1/2″ plastic tubing, a piece of garden hose and a couple of 1/2″ plastic barbs reducing to 3/8″.  Black spray paint for the OSB and copper and of course you need a water barrel.

1/5/10 solar water heater

This isn’t nearly enough copper tubing to actually get the water in the barrel “warm” in winter with freezing temperatures. However, it helps make the water a little warmer and this really was an experiment to see whether it would even work without a pump.
We originally planned on using an old water heater, but couldn’t get any of the upper plugs open. Ultimately, we want to preheat the water going into our propane water heater.

Why is the panel INSIDE?

An obvious disadvantage of the solar panel inside is that you get less sunshine for your plants. However, if we’d had more sliding glass door panels and time, we would have built a greenhouse with much more glass.

The advantage of having the panel INSIDE is that it didn’t freeze until it got down to 9 degrees the second night in a row. If you leave a solar water panel outside during freezing temps you either have to build a drainback system (no water in the panel when it freezes) or use antifreeze. We wanted to keep it simple.

ANOTHER advantage of keeping the panel inside is that the heat doesn’t dissipate outside (you can barely touch the glass when it’s sunny) and it helps heat the greenhouse.  The panel and copper of course also get warmer inside.
In spring that will no longer be desirable because it will get too hot during the day.  But it’s extremely easy to move the panel outside right in front of the barrel, just have to drill a hole for the garden hose into the plastic.

Construction:  SIMPLICITY rules
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