Sunpower is a recognized world leader in state-of-the-art, highly efficient, low mass, reliable Stirling machines. Since 1974, Sunpower, the originator of the free-piston Stirling engine (FPSE), has developed and delivered fully engineered engine prototypes and preproduction units for a variety of fields of use in aerospace, military, household appliance and research industries at power levels ranging from 35 We to 7.5 kWe.

Since Stirling engines are externally heated devices they offer great flexibility of the fuel (heat) source. Sunpower FPSE units have been demonstrated using a variety of heat sources including biomass, liquid and gaseous fossil fuel burners, solar concentrators and heat pipes.