Efficiency doesn't mean a whole lot for solar. When I say efficiency here I mean "percentage of solar flux converted to electrical power". As solar advocates never tire of pointing out, the total amount of power that falls to earth as sunlight in one day could power today's civilization for a thousand years or whatever.

No, what's really important for solar is cost efficiency, not photo-electric efficiency. The answer: printing solar cells like newspapers. They aren't very efficient, but who cares, they're cheap. Konarka and Nanosolar are two examples. I really don't think their technology will displace coal or natural gas power as the backbone of industrial power. But they'll do a nice job of counteracting my a/c bill in the summer when the sun comes out.