About the Solar Stirling Engine Racer:
A 11"-diameter parabolic mirror reflects sunlight onto the Stirling engine, heating its glass tube and causing the air inside to expand and contract. The expansion and contraction of air forces the piston to move up and down and powers the movement of its gears and rhombic drive--the same heat-to-work conversions that powered Robert Stirling's original engine in 1816. The Stirling Engine powers a small generator located in its translucent assembly, which in turn recharges the racer's AAA NiMH battery. The rear-wheeled drive racer has a geared transmission and operates for five minutes after a three-hour charge.
Here's where to get the solar Stirling engine racer.