LTD stirling engines are interesting. They harvest the temperature difference of the environment versus a cold object, and using this they power some pumps.
I don’t know the efficiency of this stirling engine, but it would be a nice idea for the hot areas of the world to put in some ice in your car and then go all the way until it melts. I don’t know how much capacity the water has as a reservoir of thermal energy, but I bet that if someone would invent a mechanism that works by this principle in a car, everybody would rush to the polar caps to sell them to the car owners.
Watch the video and comment! Your opinion is worthless!