[Edited for clarity (I hope)]
1. At least two insulated compartments serve as the
expansion/compression chambers. Preferably these will
2. In each chamber there is some
coolant (say the safest Freon alternative).
3. Each chamber has controlled valves to stop or enable
gas flow between the chambers.
4.a The chamber is heated by concentrating sunlight.
4.b. For catching the light and transfering it to heat -
(i) If the chamber is transparent, then inside there is a
dark colored material (i.e. a metal sheet, or smoke
(ii) if the chamber is not transparent then the light is
concentrated on an external section which is dark
colored, and which is not insulated, so that the gas
inside heats up.
5. For cooling,
(i) either via cooling fins when sun is not concentrated
on the chamber and fins (this is the simplest)
(ii) or via heat-bridge which is electrically connected
during the cooling phase but disconnected during heat
(iii) or via a coolant sent into the chamber during the
6. The alternating heating and cooling cause the gas
inside to alternatively compress and expand or to
alternatively liquify and evaporate.
7. The pressure changes in the chamber move a piston.
It is like a "flame eater" engine, but instead of hot flame
alternatively entering the chamber or cool air entering
it, this motor uses the concentrated sun rays
alternatively being focused on
different sections of the engine, in order to create the
The concentrated sunrays (with Fresnel or hyperbolic
mirrors or using clear plastic tubes filled with water used
as "magnifying glasses", or whatever other idea is used
to concentrate the sunlight) are alternated to switch the
phase of the chamber from heating to cooling. When the
sunrays are focused into the chamber, (and on its
cooling fins) it heats the gas inside. The rays are then
deflected to the other chamber, while this chamber cools
(or is actively cooled).
Possibly cooling elements of various sources could be
"sent in" during the "compression" cycle, and it would
still be worth the output.
An even more interesting motor of this sort could be a
section of pipe with several one way air pressure valves.
Heating up the sections in succession would cause a
continued flow of gas - with air being the easiest
(In a way, this would be analog to linear electric dc
Going even further -
Perhaps making the compartments alternating phase in
quick succession, would create perhaps an "AC" motor of
gas. (of course this is only an analogy - it would be gas
flow and not electric current, but perhaps this can be
done at an ultrasonic level, and with ionized gas, would
directly create an alternate electric current ...)