While some of the highest technology in the world is being brought to bear on the problem of saving energy, here's a guy who painted 50 soda cans black, drilled holes in them, stacked them up inside a box he made out of two-by-fours and some plywood, and what do you know? Wafting out the top was air that's 15 degrees warmer than the air going into the bottom.
He vented that warm air from the top of this box into his garage and got himself a homemade solar heater that cost less than $50 to build. The same design can be used as a solar water heater, too. It's Yankee ingenuity at its best.
Almost free garage heat - just drink a lot of soda [Hemmings Auto Blogs]