Maximum capacity of solar panels

Henry Spencer wrote:

In article ,
Alex Terrell wrote:
How many W/m2 can solar panels produce, assuming concentrated or laser
light?

Nobody has done much work on optimizing solar panels for laser illumination,
so I think the answer to that one is "nobody knows".


It's not clear what the upper limit would be, but somewhere in the range
of 2-3 kW/m^2 should be straightforward.

There are some additional advantages to using photovoltaics with lasers,
vs. sunlight. In particular, with narrow-band illumination, one can use
flat diffractive concentrators in place of curved reflectors, and can
put efficient antireflection coatings on the cell surfaces.

...Alternatively, could the laser be converted directly into heat to
drive a closed cycle engine?

Converting the laser beam into heat is no big deal in priniciple, but then
you run into the inefficiency of heat engines, and the need to get rid of
a lot of waste heat with a radiator system. Solar arrays are easier.

There are actually some ingenious schemes for various kinds of resonant
laser absorption which allow one to, in principle, get a very high
thermodynamic efficiency. Effectively, one uses the fact that the laser
beam itself has an enormous "temperature" and very low entropy. (David
Brin made somewhat bogus use of this to make a refrigerator that would
work efficiently at an ambient temperature of several electron volts
(10,000K) in _Sundiver_) I'm not aware of any efforts to make a
practical power converter based on these approaches. OTOH, the high
concentrations, and therefore high receiver temperatures, possible with
a laser would make possible pretty high efficiencies (50%) even with a
conventional heat engine cycle; it would just be a pain in the a** to
develop the hardware.

Jordin

(Alex Terrell) wrote in message . com...
(Henry Spencer) wrote in message ...
In article ,
Alex Terrell wrote:
How many W/m2 can solar panels produce, assuming concentrated or laser
light?

Nobody has done much work on optimizing solar panels for laser illumination,
so I think the answer to that one is "nobody knows".

Solar-concentrator systems are still somewhat experimental. (Note that
you have to do the concentration near the array -- it is fundamentally
impossible to concentrate sunlight into a narrow beam for long-range
transmission.) My impression is that currently feasible concentration
factors are relatively small, but I haven't followed this closely. Do
note that the better concentrator arrays generally have to be aimed quite
carefully at the light source -- they don't have the wide-angle reception
of a normal solar array.

If concentration factors are quite small than maybe solar cells won't
work. A large digger might need 100 KW. If the solar cells can deliver
400W/m2, then 250m2 is needed, assuming the laser is accuratre and
also spread over this area.

Imagine a large digger or dump truck with a 20m diameter solar array
over it!

...Alternatively, could the laser be converted directly into heat to
drive a closed cycle engine?

Converting the laser beam into heat is no big deal in priniciple, but then
you run into the inefficiency of heat engines, and the need to get rid of
a lot of waste heat with a radiator system. Solar arrays are easier.

I agree solar arrays are easier, but you have 20% efficiency of the
array and 90% efficiency of the motor = 18%. That's a lot of heat to
dump, though the array could be several meters above the vehicle.

A heat engine should be able to do better than that. The heat that
needs to be dumped would be no more than if the heat source were an
internal combustio engine - though that would be a problem in the
vacuum of the moon.

From the Making-Lemons-Into-Lemonade Department: any vehicle moving
over the regolith will have to have fenders to deflect the fine dust
kicked up by the wheels/treads; line the fenders with radiators to
dump heat into the dust.