One Small Step

Henry Spencer wrote:
In article ,
Pete Lynn wrote:
...I would expect them to use regolith
thermal energy storage to get through the night.

Unprocessed regolith is almost useless for thermal energy storage -- its
thermal conductivity is practically zero. Two weeks of continuous
unfiltered sunlight raises the temperature half a meter down by only a
degree or two.

Even with more cooperative materials, it's hard to make thermal storage
work well for two weeks at a stretch. Maybe on a very large scale.

Assume we need thermal storage of 100kW over 2 weeks of darkness at 30%
conversion efficiency = 4e11J. Lay coils of nickel tubing (melting
point 1450C) on a flat regolith surface. Use mirrors to melt the
regolith under the coils (melting point 1100-1200C) into a puddle 1m
deep and 15m in diameter. Roll (on tracks) an insulating cover over
the puddle. Run fluid through the tubing to run a thermal generator.
During daylight, roll back the cover, use the same system to power the
base.

So it seems to be doable but the mirrors would need to be a few 1000m2
and there's lots of moving parts.

I still prefer nice predictable, no moving part photovoltaics scattered
in a belt around the Moon, beaming their energy over the surface where
needed through microwave waveguide towers. If the linkage is
interrupted, the base could use fuel cells as emergency backup while
the break is repaired.

Another possibility is to use aluminum-air batteries. Any lunar base
is likely to develop mining/refinig capability which would necessarily
produce the aluminum and oxygen these batteries run on. The batteries
are refreshed by replacing/recycling oxidized aluminum which would
dovetail well with the refining activities. If vapor phase separation
is used for refining using concentrated sunlight, no photovoltaics are
required at all.
Steve Mickler