Lasers are a reasonable option for energy transmission - and they'll likely take over a lot of space communications in future. But I don't think Project Prometheus has much to do with lasers. I agree Gary's "hidden agenda" is the military applications, but ANYTHING that can store and deliver large amounts of energy from space has roughly the same military application: hydrogen + oxygen does rather well at that, for example. The main difference between different energy options is the rate at which they can deliver their energy, and other than actual nuclear explosions, I think chemical combustion has proven to be pretty much the best option at extremely fast energy delivery rates for space applications.

Why the interest in nuclear reactors then? There's a big segment in the general science community that still thinks nuclear is cool - the Manhattan project was mythical glory days for physics in the US, and they want to get back to that somehow. Despite the expense and dangers and waste, physicists collectively thirst for a much greater role for fission in our society. Fission still seems like "science", while all those other technologies are just "engineering". Hence scientific support for JIMO. That's my theory anyway :-)

Getting back to global warming... Solar Power Satellites are of course one of the best options - the big issue relative to terrestrial solar is energy conversion and transmission efficiency. If you're losing 80% of the energy you capture in the conversion to laser light and transmission and capture of that light again on Earth, the SPS has absolutely no advantage over the same energy capture technology on the ground. The great thing about the microwave techniques Brown and Glaser looked at is the (at least potential) high net efficiency. If you can do the same with lasers, all the better because lasers otherwise greatly expand the practical deployment options (like allowing Earth-Sun L1).