[DennisP]

A year ago I read the book The Case for Space Solar Power, which goes into the engineering in detail.

The old SPS designs from the '70s were monolithic beasts that would have been ridiculously expensive. Current designs would use a large number of identical parts, of about eight types, which would self-assemble in space. That way they can be mass produced in factories.

The basic design was PV with microwave transmission, which has already been tested over distances of ten kilometers or so. (Iirc it was between a couple Hawaiian islands.) The receiving station sends a sort of homing signal for a phased array transmitter, which makes it difficult to redirect to somewhere without the homing signal and keep a reasonably focused beam, though you could switch between multiple receiving stations (which are fairly cheap). The station would be in GEO.

The book did some detailed cost analysis and found that with pre-SpaceX launch costs, the SPS could provide power at 15 cents/kWh retail.

Elon Musk has said that at scale the BFR could ultimately get to a $50/lb launch cost, so for grins I plugged that number into the book's calculation and got 4 cents/kWh.

Since this type of solar would work through the night, with little or no need for storage, it could be pretty competitive.

book: https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...

[AstralStorm]

It would be competitive, if there were no nuclear power or maintenance costs or manufacturing costs. These are not counted in launch costs.

You have to launch replacement panels pretty often due to trash collisions or put them in a less than convenient orbit.

The space solar module with a good enough battery and emitter would cost about as much as half a radiotelescope... Because it is one.

And consider we have problems covering sizable area with wires and cheap panels which are easy to maintain.

[DennisP]

The costs I quoted include everything, including manufacturing and maintenance. The book breaks down all these costs. In the 4 cents/kWh scenario, launch isn't the dominant cost anymore, and dropping that further wouldn't make much difference.

You don't put a battery on a solar power satellite. To whatever extent you need battery, you put it on the ground, but you don't need much because a satellite in geosynchronous is in full sunlight almost all the time.

[AstralStorm]

You want to put it in synchronous? How do you keep it lit up all the time?

You do understand you need many more panel fields as opposed to receiving stations that way and half of them is wasted anyway?

I thought the idea is to put them in solar Lagrange or solar synchronous orbit and bend or reflect the maser to stations. 24 hour lit, though a bit trashy if Lsun is used.

The math is suspicious anyway. Wouldn't it mean that the panels would cost 25% of this on ground?

[DennisP]

Due to axial tilt, for most of the year geosynchronous satellites are in full sunlight 24/7. Twice a year, around each equinox, there's a period of 44 days during which the satellite goes into shadow briefly each day, for a time ranging from 2 minutes, to 72 minutes at the maximum.

https://corpblog.viasat.com/how-satellites-are-affected-by-t...

This compares pretty favorably to capacity factors of other power sources.

Illumination per square meter averages quite a bit higher than ground solar, and except for the brief times in shadow is 30% higher than ground solar at noon.

The book evaluated other locations including Lagrange points. Everything had pros and cons; the main disadvantage of Lagrange points was the greater distance, requiring bigger antennas. I think more delta-v in deployment was a factor too, though I forget by how much.