This is the coolest DIY project I have seen in a long time, and definitely an interesting project if you want to live off the grid. Fifteen columns of soda cans are used to harvest the suns rays and provide some pretty good water heating performance.

According to the maker:

Peak BTU performance was observed during the noon hour period in October 2001 wherein the temp rise was 50 to 54F degrees resulting in a 9000 to 9720 Btu or 2636 to 2847 Watts. Peak BTU performance will actually increase in colder weather due to the rise in temperature between input and output temperature and a lower angle of incidence.

What you need is a whole lot of soda cans, some conductive black paint and the time, patience and skills to pull a build like this off. Check out the video for some more technical details. [Cansolair via Hacked Gadgets]