Ok, I think whoever came up with this is pretty brilliant... Basically, they pave a section of the sea floor. Rubber fins move back and forth with the tide. The fins create suction and pull air down, through turbines, generating electricity. The lack of moving parts means less damage to the marine ecosystem (if you don't count paving the ocean floor) and if they built the system under the Golden Gate bridge they could generate twice the energy required by the city at its peak energy need. http://www.msnbc.com/news/910115.asp