I have long been a fan of alternative energy solutions, although I am ashamed to admit to a certain sluggishness in applying them to my life. I have, though, taken some steps to reduce the energy I use, and thereby the pollution I produce, comforting myself with the “progress, not perfection” aphorism — and I believe in this principle. But to justify rationalizing my own life with it, I need to strive for and achieve progress, at least now and then.
Recently, I was researching solar power (again), looking to see if solar products for the suburban homeowner had gotten more efficient and/or more reasonable in cost, when I ran across an interesting idea. I have known for a long time about passive solar building design that strives to maximize thermal efficiency, and have intended to use this suite of ideas in building my own home when that day finally comes. However, I had not thought usefully about using ideas like these in my existing home. Then I saw a clever, simple, and fairly cheap design for a passive solar air heater analogous to the passive solar water heaters we’ve seen for many years (another very good idea: Solar Water Heater).
The concept is simple: build a frame out of 2x4s and back it with a piece of plywood (or similar). Line the back of the inside with a piece of 1″ stiff insulation, and cover that with a piece of sheet metal that you’ve painted black. Overlay some baffles built from 2x4s (to increase turbulence and hence pick up more heat from the back plate), and cover the whole thing with a sheet of clear glass, Plexiglas, or the like. Cut two 4″ holes at the top and bottom of the back, and attach a computer cooling fan to the hole that will serve to discharge the warmed air (the top one). Attach a 12-volt solar panel to power the fan, which turns out to be small and cheap. Attach insulated, flexible, 4″ ducting to the input and output holes, with a one-way flapper valve (like you use for dryer ducts) on the discharge side, and run these hoses to the space you want to heat. A nice optional component is a thermal switch that only starts the fan when the heater’s interior temperature gets warm enough to be useful (say 80 degrees F). Attach the whole unit to a frame so that it’s stably oriented for maximum solar influx (South and up), and you’re done.
Obviously, one small unit like this won’t heat your entire house, garage, shop, or trailer, but every little bit helps. I haven’t determined yet how much total surface area you’d need to heat an entire house, but again, every little bit helps. Here’s a video that shows how two guys did this:
Enjoy, and good luck. I’d love to hear how this works out for anybody who tries it.