NASA GRC Stirling Research Lab

The efficiency of conversion from thermal to electrical can be increased significantly by using the Stirling thermodynamic cycle
•Alternate heating and cooling on volume of gas creates a pressure wave that drives a piston attached to an alternator
•Heat can be supplied by any source –radioisotope
•Cooling must also be provided for the waste heat portion of the cycle –radiant heat transfer to space
•Up to 40% thermal-to-electric efficiency
•Dynamic : has moving parts
Cycle operation:
•A displacer shuttles gas between the hot and cold ends to raise and lower the gas pressure
•With displacer at the top, gas is pushed towards cold end, lowering the pressure
•With displacer at the bottom, gas is pushed towards the hot-end, raising the pressure
•The piston’s mechanical energy can then be utilized as desired –for electrical power it is coupled to an alternator
•The motions of the piston and displacer can be controlled by mechanical linkages (kinematic) or by the working gas pressure (free piston)