[hatcravat]

Who cares about the efficiency when solar panels weigh over 50 kg per kW? Even at SpaceX prices, the cost of launching a solar panel into space is hundreds of times the cost of the panel. If your alternatives are "buy 500 panels and put them on the ground" and "buy one panel and put it in space," why the hell is anyone even remotely considering the second option?

[Solarsail]

Wasn't the original concept for SPSS (at least in O'Neils The High Frontier) to build them out of mined asteroid materials? At that point the cost of the proposal is disconnected from the cost of launching the panels. I've heard many analyses of that which do suggest the economics of it is inevitably atrocious for ground-launched SPSS. Cost numbers for asteroid mining vary by a couple orders of magnitude though, which mitigates the above...

[schiffern]

So now instead of launching panels, you're launching a panel factory. Actually you're launching their entire supply factories too (mining, high-purity silicon boule manufacturing, wafer cutting, smelting metals for busbars and backing, etc). None of this has been done in microgravity before. Everything will need mass optimization, and you need provisions for maintenance and repair on all these systems.

Doable? Sure. But you have to make a lot of panels before it pays off.

[dredmorbius]

It could be worse:

http://discuss.joelonsoftware.com/?joel.3.219431.12