Surprisingly it appears not to be too far off standard solar panel efficiencies. According to this source[0], five nines silicon (5N) is called Upgraded Mettalurgical-grade (UMG) silicon. According to this paper[1], efficiencies over 20% have been reached with UMG silicon.

[0]http://www.greenrhinoenergy.com/solar/technologies/pv_manufa... [1]https://www.sciencedirect.com/science/article/abs/pii/S00380....

I mean, how many of these do you need to produce as a seed? You certainly don't start the process at full capacity; if there are ways this nests into an evolving, self-reinforcing system to prepare for human contact then it's a fantastic start.

It's not like we have huge space constraints for small starts, I reckon?

99.999% is what we used in our 156.25mm x 156.25mm polycrystalline cells when I did solar manufacturing. 21% efficiency was easily obtained, allowing ~300w in a 60-cell panel.

However, there's no atmosphere or weather to worry about on the moon, so I'd expect that to improve efficiency quite a bit compared to the Earth.

The real challenge with solar power on the Moon remains the two-week day/night cycle, which means either massive batteries (impractical) or awkward polar cliff locations to minimize the hit.

Or a (partial) ring around the equator, video game style.

There is a thin "atmospheric" layer of molecules floating around the lunar surface. Indistinguishable from vacuum for most purposes but it might affect that many 9's of purity.

https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphe...