I just got back from a conference on this in Spain -
http://www.congrex.nl/04c15/

It was very interesting - I'm hoping to write up a lengthy article about it in the next few weeks.

If you look at current installations of terrestrial photovoltaics, the bulk of it is being done in Japan, which is also the location with the bulk of world production of photovoltaics. Japan's energy situation is perhaps the most acute in the world, for an industrialized country - it has a little bit of its own coal, but very little else in energy resources.

Europe is not too far behind Japan - particularly Germany, which has strong incentives for solar installations. Anyway, the huge demand from these countries, despite their own production facilities, means they are also importing a good fraction of production from other parts of the world as well - including the US. Volume has been going up 20-30% or more per year the last few years, worldwide. Anybody who really has a cheaper usable photovoltaic system stands to make billions of dollars quickly in today's market!

Anyway, on the SPS question - interestingly enough, while the US has done essentially nothing on this the last few years (Bush and Cheney killed the program NASA was just getting started on in 2001), Japan and Europe have been really ramping up. Of the roughly 80 people at the meeting last week, close to half were from Japan, and they have some 200 people working on several specific designs for solar power satellites right now, both under Japan's Science ministry, and under the Trade and Industry ministry, as well as some indepenent university groups. At least some people are very excited about the prospects :-)