Solar power or nuclear power?

One concept worth considering is bootstrapping. Perhaps the first mission
could be a solar cell factory.

Ron Menich

hollroa@...
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I have been making some rough calculations of the efficiency of solar and
nuclear power sources for use on the moon. The initial O'Neill plan called
for the export of 3 million tonnes of lunar material per year. This export
rate is really quite large and it calls for an installed round-the-clock
power capacity, of some 500MW on the lunar surface. A less ambitious plan,
would be an initial base capable of exporting perhaps 200,000 tonnes per
year. This calls for a more modest power capacity of perhaps 20MW round the
clock power. Given that the initial power source will have to be imported
from Earth, which type of power source is likely to be more effective?
Solar PV, Solar thermal, or Nuclear? or maybe a combination of solar and
nuclear power?

I have been reading through NASA litterature on space nuclear reactors.
The SP-100 space nuclear reactor, would be capable of generating 850Kw,
round-the-clock power, with a core life of 7 years. The complete power
system, including power transmission to base, transformer system, heat
sink, etc, was projected to weigh around 20 tonnes. That gives a total
power output of 42.5 W/Kg. Only a small amount of astronaut work was
thought to be needed. The reactor shielding was provided by the bulk
regolith itself. The astronauts would dig a hole approximately 3 metres
deep and maybe 2 meters wide and place the core at the bottom of the hole.
The setup could be up and running within 1 week.

On the other hand, solar PV systems can be made extremely lightweight.
Some PV panels mass about 2Kg/M2. The support structure and suntracking
equipement is unlikely to weigh much more than 2Kg/m2. A 20% efficient
solar power system, could produce an average round the clock power output
of perhaps 34w/kg. This figure is only 20% less that the specific power of
a nuclear reactor. Critics often argue that the use of solar power systems
would entail importing hugely heavy fuel cells from Earth. This arguement
does not strike me as being true. The only base systems that are required
to function during lunar night are life support functions. These could
easily be powered by a small SNAP reactor or RTG. Given the large
development costs and development timescales of nuclear power systems, it
seems dubious to suggest that nuclear power systems are likely to be more
economic that solar PV systems.

However, all of this assumes that the power sources have infinite
lifetimes. Solar PV systems suffer radiation damage from solar events and
galactic cosmic rays. A solar power system may not survive much longer than
10 years. A nuclear system on the other hand, can be refuelled several
times within its lifetime, so that reactor life is extended to perhaps
20-30 years.

Which system is best? Would it be wisest to assume that a combination of
the two systems would be more approapriate?

Tony