One further note, with speculation. High pressure hydrogen is by far the best working fluid for the Stirling engine.
Containment of the working fluid during operation of the engine at high temperatures and at high hydrogen gas pressures is essential for the Stirling engine to be an alternative to the internal combustion engine. Most commercial iron alloys are permeable to hydrogen at high temperatures. There are easy solutions to this problem. For instance, many metal oxides are impermeable to protons. However, the interesting thing from the POV of anyone who has studied LENR, or the hydrino, is the possibility of combining an active metal matrix on the "hot side" for hot hydrogen in a Stirling. This could be used either in conjunction with solar, or ideally, by itself. One possibility that comes would be a "sponge" of Ni on the hot side. Mills/BLP for several years worked with gas phase, but AFAIK they only used very low pressures (fractional atm). This was to achieve easier ionization, but it is not feasible to combine low pressure with a Stirling. However, it is possible that in theory at least, that the ionization could be via radioactive decay. A Compund Stirling - using a H/He working medium and with a sponge of Thorium on the hot side would be interesting. Jones
