"Green" Energy?

Well i like in the U.K. so i would suggest wind energy because of all the wind we have! But for the U.S. I'd guess solar power, just saying this because I assume everywhere's more sunny than the U.K.!

I'm Norwegian, so of course it's water power. But for the US and the rest of the world, I really hope they manage to get energy off of particle fusion.

I would say no 1 technology will ever dominate the hole world. But regionally different technology will dominate the area. In areas where there is a lot of sun like in desserts solar and/or solar thermal will naturally dominate. In areas where there isn't much sun but there is sufficient wind, wind turbines will be your obvious choice. Areas that have lots of rivers will build dams. Once fusion technology takes off they will be sprouting up all over the place.

With generating energy it is important to be able to deliver energy "on demand" not just when the sun is shining or the wind is blowing. So even regionally they will have to use several technologies until the time comes where energy can be stored cost effective. The sun doesn't always shine and the wind doesn't always blow at the same strength so output will vary.

Solar panels on Earth's surface -> Nuclear Fusion reactors -> Solar arrays orbiting the Earth

The Sun is more powerful than any nuclear fusion reactor we could ever build (cheaper to use the Sun instead of our own resources, anyway), so the obvious path of advancement is to get by with solar panels on the surface and tiny (compared to the Sun) fusion reactors here on Earth until we have the technology available to send entire solar arrays into orbit which would then transmit the energy down to Earth for us to use.