Mount flat vents on the top of cars that have have little heat, wind, turbines to charge the car batteries. When parked in the sun the vents can be opened and vent heat from interior.-- Imathinker, Jul 05 2004 Heat - powered fans http://www.halfbake...0-_20powered_20fansNo batteries. [phoenix, Oct 17 2004] Weird, I was just thinking about a rooftop whirligig generator, but for houses. With how hot cars get in the summer I think it's a fine idea to use that excess heat. Too bad it would not work as well in the winter when it would be needed the most.-- 2 fries shy of a happy meal, Jul 05 2004 Without a continuous supply of fresh air I don't think you're going to capture much energy.-- phoenix, Jul 06 2004 random, halfbakery