Solar Power Satellites

--- In spacesettlers@yahoogroups.com, Ed Minchau
"the efficiency of the system would be 99% (less frictional losses)."

I think the introduction of heat engines and turbines is an
interesting possibility. Von Braun envisaged just such systems
before the advent of solar cells.

But, there are two conversions: from solar insolation to kinetic
energy and then from kinetic energy to electricity. While the
theoretical maximum efficiency of the first process might approach
100%, there's an awfully long way to go from 1-Tc/Th to something in
real life.

Very large scale modern electric generating plants with a theoretical
maximum Carnot efficiency of about 1-300/1500 = 80% operate at
efficiencies below 40%. If the same ratio held for a plant operating
with a Carnot efficiency of 99%, the efficiency of conversion of
solar insolation to electrical energy would be about 50%, which, I
think, is much more realistic. It is still an efficiency more than
double what current commercially available photovoltaic cells deliver.

It's interesting that this early 19th century technology is so
superior to some darlings of the early 21st century. The
disadvantage to any mechanical system, of course, is moving parts,
and the vastly more complex problems of operations and maintenance.

Interesting the theoretical maximum efficiency of a solar powered
heat engine on Earth could be as much as 1-300/2000 = 85%. Even
higher is heat failure of materials weren't a concern.

Bob