So, although it may be too expensive for Earth power, it can be very practical for moon power.
There's a famous-in-the-area ex-NASA blogger with good (not perfect) articles on the topic, but I can't Google and find him 'cause authoritative institutions now seems to trump and drown out mere experts on Google.
Others here cite him: https://caseyhandmer.wordpress.com/2019/08/17/blog-series-co...
Maybe better: nuke the moon and reduce a few key crater rims, then use much shorter towers. Could be that a series of regular bombs might be more effective and less likely to "alarm the horses (general public.)"
Dust.
There is near a Moon base, which is presumably where you’d need power.
> it's economically reasonable to loop the moon with a 600Ω conductor
Could you generate nontrivial power from the Moon's motion through the Earth's magnetic field?
Not sure, but my gut feeling says no: the Moon is a very long way from the Earth relative to the Earth's size, therefore the magnetic field is likely to be fairly uniform around the Moon and so that can't extract much work.
That said, one fun idea I've had is to just assume that the Dark Energy expansion of the universe is pushing the Moon away very slowly; 73 (km/s)/Mpc * distance to the moon ≈ 9.5e-10 m/s, which is pretty close to the actual current Moon-Earth recession speed.
Plugging that into the formula for far-field gravitational potential energy given the mass of Earth and the Moon, that's about 170 GW at the present time.
(But don't go trying to crowd-fund a Dark Energy field reactor on my say-so: At my [rather limited] level of understanding, it looks like physicists haven't yet reached any sort of consensus as to whether or not Dark Energy might work like that).
What would the cable layer look like? A huge robotic rover? Could you get all 10,000 km onto one spool, or deliver new spools to it?
It's a Starship-scale project: something like 100 launches, which is only feasible because Starship is targeting such low launch costs.
I don't know (see previous disclaimer) but I wouldn't be surprised if (assuming circumlunar power is even the chosen solution) this is done by sending up an aluminium factory instead and processing regolith.
1. A moon day is 28 earth days, thus 14 days of darkness
2. Ice are in permanently shaded areas near the poles of the moon, it might be easier to setup satellites to beam down power rather than setting up in 2 locations
For Luna it doesn't make as much sense as it would for say Mars, since there's no atmosphere to reduce efficiency and no shortage of ground real estate. You can save a bit of propellant to not bring the panel assembly down, but you'll need fuel for orbital stationkeeping instead anyway.