This simple engine is beginning to be looked at again as part of systems for generating electricity, perhaps in combination with superheating solar power etc. I just love the fact that they are relatively simple and easy to build!!

Animated Engines, Two Cylinder Stirling: “The Stirling engine was invented in 1816 by Rev. Robert Stirling of Scotland. The Stirling is a very simple engine, and was often billed as a safe alternative to steam (since there's no boiler to explode). It enjoyed some success in industrial applications, and in small appliances like fans and water pumps, but was eclipsed by the advent of inexpensive electric motors.3 Since it can run on any source of heat, it now holds promise for alternative fuel engines, solar power, geothermal power, etc.”

Also see here for the wikipedia entry on Stirling Engines