Frank Grimer.
Although the Crookes Radiometer engine can convert the
kilowatt (~ 1.3 Hp) per square meter solar insolation into work
quite efficiently, it's a bit cumbersome to work with at
the ~ 0.2 torr vacuum pressure.
As an alternative I propose a vertical axis heat pipe that
wicks a working fluid from a pool at the bottom where it
wicks out from the pipe through closely spaced-wicked plates/vanes heated
by sunlight where the vapor exits through orifices "jets" at the tip
of the vanes. Adding "centrifuge enhanced wicking" too.
Water from the thermal/liquid syphon pool at 25 C (77 F) has a vapor pressure
of about 25 Torr, but, heated by sunlight on the vanes to 70 C (158 F) it has a
vapor pressure of 233 Torr. This offers a 208 torr pressure difference and a
Carnot efficiency of 343-298/343 = 13%. Kerosene or JP-4 will work at
higher vane temperatures.
OTOH. If you heat the pool with a radioisotope "stove" to 1000 K or more
using mercury, potassium, or lithium, as a working fluid you can zip right up into
the serious shaft power range with only one moving part. :-)
Fred
