The Energy Fix  Engineering Triumphs Over Wave And Tidal Forces  Sept 17 2013

How water could be harnessed for roughly a third of U.S. annual electricity usage.

The Bottom Feeder

Water is 800 times denser than air, and building a gen­erator able to withstand the tremendous force it generates has hampered the development of next-gen hydropower. If engineers can harness its energy, water holds great potential: about 1,420 terawatt-hours per year, or roughly a third of U.S. annual electricity usage.

http://www.popsci.com/science/article/2013-05/future-energy-water