Stirling Engine

There's a company out in Phoenix called Stirling Energy Systems that has a cool idea for solar power. Instead of a large field of solar panels, they use parabolic dishes to focus the sun's rays onto a chamber of hydrogen, which heats up and pushes a piston to generate electricity.

The idea behind it all is the Stirling engine. You could probably freak some people out with this model; set it on a warm surface and it will basically run forever.

You can find plans online to build your own Stirling engine.