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Energy found in water (in the form of motive energy or temperature differences) can be harnessed and used to generate electricity. Since water is about a thousand times denser than air, even a slow flowing stream of water, or moderate sea swell can yield considerable amounts of energy.

Prototype energy-harnessing buoys, that use a permanent neodymium-iron-born magnet which is forced back and forth through an electric coil by the modulation of waves, are currently in use off the coast of Oregon. The researchers believe such buoys could power about 20% of Oregon’s electricity needs when fully implemented and operational. This is currently the U.S.’s only university research program into ocean wave energy extraction funded from federal resources.

Now that the prototypes buoys have demonstrated their potential, a study is underway to consider impacts on sea birds and marine life from electromagnetic fields, construction, deployment, and servicing of undersea cables.

In addition, the Federal Energy Regulatory Commission has put the spotlight on this potentially valuable source of renewable energy by announcing an interim policy, and inviting public comment on how to process preliminary permit applications for ocean energy: wave, current, and instream hydropower technologies. The Commissioners expressed interest in promoting these technologies, but also concern about their reliability, environmental and safety implications, and commercial viability.

Tidal Power

It takes a high tide and a special configuration of the coastline, a narrow estuary that can be dammed, to be a tidal power site of value. Only about nine sites have been identified in the world. Two are in use and generate some electricity. Damming estuaries would have considerable environmental impact. The Bay of Fundy in eastern Canada has long been considered for a tidal power site, but developing it would have a negative effect on the fisheries and other sea-related economic enterprises. It would also disturb the habits of millions of birds, which use the Bay of Fundy as part of their migration routes.

Within about 25 degrees each side of the equator the surface of the ocean is warm whereas the depths are cold. This temperature differentialcan be a source of energy. A fluid such as ammonia (which at normal atmospheric temperature of 70 degrees Fahrenheit is a gas) is condensed by colder water pumped from the ocean depth, and then leftt to warm back up and turn to back gas. The resulting change in gas pressure can move a turbine to turn a generator. But the plant would have to be huge and anchored in the deep open ocean subject to storms and corrosion, and the amount of water that has to be moved is enormous, as the efficiency is very low. OTEC does not appear to have much potential as a significant energy source at this time.