The GE Ecomagination contest is almost closed for voting, running to the end of September. There are some good proposals there, and a lot of amusing ones. If you care to sign up to vote, I'd recommend
Hydrothermal Generation and Mining:
Hydrothermal Vents as a Constant, Uninterrupted Source of Multi-GW Energy : View Idea
Small, high-efficiency generator using any hot source, such as exhaust. (40% at 700C, all metal.)
High efficiency power generation device using any fuel or heat source : View Idea
Cheaper tidal generators, etc, - one I just wanted to get out there, because it bugs me to see conventional windmills being stuck on the ocean bottom.
http://challenge.ecomagination.com/c...D-F7DC0B898A24