sterling engine

[Ray Watts]

what is a sterling engine

[mikewith]

Andromeda explained this earlier: A Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side it expands and pushes up on a piston. When it moves back to the cold side it contracts.
They are incredibly efficient, able to get upto 50% efficient (this is v. good!). I have always wanted one that can run on the heat of your hands or strong sunlight (not that you get any round here!).