Naquada

Seriously though, I think we'll go to greener forms of energy (wind and solar) for some time while hydrogen and fusion are perfected.

There have been a few new innovations in solar power recently, including test Boron cells that are about 50% efficient, much better than the best GaAs cells which go up to 23%. But those were just lab tests. It'll take a lot of funding and research before we're able to utilize them on a large scale.

That being said, I've read that if every suitable roof in London was covered with silicon solar cells that perfom better in low-light conditions, then all the power needs of the city would be met. I'm not sure how true that is, but it's an interesting thought.

Another thing to consider with solar and wind power is that DC power is produced. Transforming that into AC power is quite inefficient and probably a bad idea if you're going for efficiency. So the power source would need to be located close to the load, and DC applicances would need to be mass-produced.