www.thegoodhuman.com/2009/06/09/solar-space-heater-made-from-soda-cans-an-old-window Quite an interesting concept!! Would be QUITE USEFUL in the colder months for sure!
theres much better models out there https://www.youtube.com/watch?v=Jzxw1j-dzY4"]Pop soda beer can Solar Powered heater furnace panel -- Part 1 - YouTube