The Stirling engine – invented in 1816 by Robert Stirling – uses temperature difference to activate its gas-filed pistons. The engine is efficient at generating mechanical power, although slow. But the research lab thinks it could be ideal for use in a solar-powered aircraft that needs to fly throughout the night on stored energy.
Instead of using solar cells to convert sunlight to electricity, and store it in rechargeable batteries, the plane would use a thermal battery that stores heat in order to drive its Stirling engine.
During the day, sunlight will heat a mix of lithium and lithium hydride and a moving parabolic mirror will keep track of the Sun to focus its rays on the thermal store. While the Sun’s rays will provide heat for the engine’s gas, the cold air outside the plane will provide an ideal way of lowering its temperature.
Liquid Hydrogen is the only known fuel suitable for aviation to be produced from renewable energy sources and offering extremely “Low Pollutant Emissions”.