As it seems we have now included the actual solar powered engines (Sun Motor & Sun Runner) of Solar Engines of Phoenix Arizona, and by extension, PM Research as well, I'll include here a link to another great Forum where I did a thread on some comparative experiments between the two engine types.
... into a Thermodynamic Comparison of two Stirling Cycle Engines. Perhaps better entitled simply "Messing about with a couple of Sun Motors", but the
Sadly, it seems that the accompanying YouTube videos have been decoupled from that original thread, but I can probably post them back up here if there is interest!?!?