Building a solar panel heater out of aluminum cans is not as far-fetched as you might think. A company in Canada, Cansolair, Inc., specializes in building these units and has won awards for their design. Their heaters have been described as "green energy and recycling all rolled into one", and have proven to be very cost effective and efficient as well.
How They Work
The units are typically installed on the outside walls of houses, and of course, in a location that gets a lot of sun. The idea is to draw air from near the floor of any room in a home, and pass it through the heating panel, which contains several columns of cans. The air is then returned to the same room near the ceiling. The cans are stacked and have large holes cut in both ends to allow the air to pass inside them while the outside of the cans is getting hot from the sun.
Do It Yourself!
You can build a simple solar panel yourself out of aluminum cans.