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The 70% of the Earth's surface which is covered by oceans is thought by some to hold significant potential toward meeting the growing energy demands of civilization. Among the promising renewable energy sources found in our oceans are ocean thermal energy, wave energy, current energy, and offshore wind energy. Some of these energy sources are already being applied in parts of the world and others are in early stages of development. Each of these deserves consideration, as humans seek renewable and clean sources of energy.

Ocean thermal energy comes from the temperature gradient that naturally exists in the ocean. The surface waters are warmed by the sun and deeper waters stay cold. A heat engine is used to convert the thermal energy as it transfers to a colder reservoir. There are various system designs but all involve a huge pipe that is submerged a mile or so into the ocean's depth to bring very cold water to the surface. Two ocean thermal energy plant projects on the drawing board are one by the U.S. Navy in the Indian Ocean and another by a U.S. company in Guam.

The oceans tides are driven by the gravitational pull of the moon. Waves are driven primarily by wind and currents are driven by many factors, such as salinity, temperature, topography and the earth's rotation. All of this movement represents mechanical energy that, in principle, could be harnessed and converted to electricity.

Several devices have been developed to extract energy directly from wave power. The oscillating water column traps a column of water which is moved up and down by wave action like a piston and is connected to a turbine. The point absorber is a floating device with parts that move with the waves and drive electromechanical or hydraulic energy converters. Attenuators look like giant swimming pool noodles and float parallel to the direction of the waves. The flexing motion of the attenuators drives hydraulic pumps. Places with the strong and constant wave power, required to consider this developing energy source, are the coasts of Scotland, northern Canada, southern Africa, Australia, and the northwestern coasts of the U.S.

Ocean currents move in complex patterns across the planet, but the movement is constant and in one direction only. Because water is 800 times denser than air, a 12 mph current has as much force as a 110 mph wind. Ocean currents, therefore, contain an enormous amount of energy. The U.S. Japan, China and some European countries are pursuing the possible use of Marine Current Energy. Proposals exist for submerged water turbines that would look like giant windmills. This is in very early stages of development and there are currently no grid connected turbines.

Offshore Wind Energy operates under the same principals as on land. Wind driven blades power generators to convert wind energy into electricity. Denmark and the UK have large offshore wind facilities. Proposed offshore wind projects are in the works in the U.S. Canada, Asia and other parts of Europe.

Exploiting the ocean for energy is not without environmental concerns. The impact on marine life and migrating birds, interference with the navigation of certain species, emissions, visual impact and noise are all factors to consider as humans venture into new frontiers in search of better energy resources.

Learn more about this author, Emily Cathcart.
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