[plasmatorch]

I worked on this project a few years back, on the power transmission bits. It's pretty cool from the engineering side; the mechanics need to be very light, and unfold into a large area. The beaming part is just a large phased array. The hardest bit is likely high efficiency, cost effective PV cells that can survive in space, but this is a field that Atwater has been in a long time, and is very, very good at.

[pencilguin]

Probably a laser would be a much better power transmission method: shorter wavelengths spread out less. You would pick a wavelength that PV panels on the ground convert most efficiently, and pump the laser cavity with focused sunlight, directly. No fooling with PV panels, then. Monochromatic light can be converted via PV with little loss.

Mirrors to focus sunlight weigh practically nothing. Made of alternating layers of different index of refraction, of thickness according to the pumping wavelength, they reflect only that wavelength, and let the rest pass through. So, the laser cavity doesn't get hot, an important detail in space where cooling is hard.

You would arrange so the laser light intensity is no more than of sunlight, for safety.

Of course it wouldn't do much good in the daytime, but would work at night and in winter. Just, not so good through clouds.

[pipodeclown]

Isnt this really a question the reflectivity and amount of absorption in the atmosphere of the wavelength you're using?

[kumarvvr]

Any info on system capacity and efficiency?

[plasmatorch]

IIRC, it took about 50~100 W from a power supply to beam ~2.5W to a target antenna array, but that was fairly early on, so it's likely better now.