Free energy that runs a heat powered Stirling engine using Fresnel lens

There's an old adage that says "from acorn to an oak tree", there were lots of innovative ideas conceived in the past which may seem irrelevant at one point but was put to good use afterwards, an example of this is the development of the steam engine by James Watt which led to a large number of further developments. This video demonstrates harnessing the energy of the sun to power an engine using a Fresnel lens capable of taking twelve square feet of sunlight concentrated to as little as one inch of area. The power of concentrated sunlight collected in the magnifying glass has a beam temperature exceeding 2000 degrees Fahrenheit which provides all the heat needed to run a heat powered Stirling engine fitted with a piston enclosed in a cylindrical chamber filled with gas, the gas is usually non compressed air although hydrogen is more preferred, when the gas in the chamber is heated by the concentrated heat coming from the lens it builds pressure that expands to push the piston, providing the power stroke that turns the connected flywheel which is also connected to another secondary piston that pushes the cooled gas back to the primary piston, developing a repeated cycle of the process.