This is the same solar stirling engine with a strong Fresnel Lens. The steel wool adds power to the stirling displacer piston as the light has a good focal target INSIDE the glass chamber Dramatically increasing efficiency. This is very important as most Stirling Engine lose 50% of their heat into the surrounding air. A vacuum would be even better. Also, because the glass chamber easily removes with a rubber O ring fitting, air can be replaces with a custom heat exchange gas.