The Stirling engine is a type of heat engine. In simple terms, the Stirling works by very efficiently converting heat energy to mechanical energy. It is considered to be one of the most efficient types of engine.
Any source of heat can be used for a Stirling engine, including solar, waste heat, or burning various fuels. Stirling engines are typically larger than internal combustion engines (or to put it another way, a Stirling engine typically produces less power than a similarly-sized internal combustion engine), limiting use in vehicles.
Inventor Dean KamenW is developing a roughly one cubic meter Stirling-powered electrical generator which he hopes will be widely adopted for use in developing countries and rural locations.