Energy can be obtained from ocean waters in three ways: from the waves of ocean, high and low tides and from the temperature difference within the water of the ocean. As such the total energy obtained by each of these methods is very less; hence there are very few power plants throughout the world.
Methods of Utilizing Ocean Energy
Oceans cover almost 70% of the surface of the earth carrying enormous energy that can be tapped for various purposes including domestic and industrial. Observing the huge quantities of water, and large waves in oceans the engineers may be tempted to think of using them for producing power.
Energy can be obtained from ocean waters in three ways: from the waves of ocean, high and low tides and from the temperature difference within the water of the ocean. As such the total energy obtained by each of these methods is very less; hence there are very few power plants throughout the world that utilize ocean energy. Let us see the three methods in more details.
1) Energy from the waves:
Large waves are formed in the ocean waters continuously carrying large amounts of kinetic energy which can be converted into the electrical energy. The waves can be used to run the turbines directly and generate electricity. This method is used for generating only small amounts of power say for the small light house or for the local communities. See the image below (Image source: http://www.burningenergy.com/images/view/44/waveenergyhiresosutextjpg.html)
2) Tidal energy:
During high tide the level of water becomes very high and during this period the ocean water can be collected in the large reservoirs acting as the dam. During the low tide the level of water near the shores becomes less and the water from the reservoir can be made flow to the lower level over the turbines just like in the traditional hydroelectric power plant. The shaft of the turbines rotates in the alternator generating electricity. The tidal energy power plants can be setup only in places where there is large difference extending beyond 16 feet between the high tide and low tide. The major drawback of the tidal power plants comprising of the turbines setup is the danger they can cause to the plants and animals in the estuaries. See the image below (Image source: http://www.alternative-energy-news.info/technology/hydro/tidal-power/)
3) Energy obtained from temperature difference of water:
The temperature of water on the surface of the ocean exposed to the sun is higher than the water in depths of the ocean. In some cases the difference between surface water and deep water temperature can be more than 40 degree. This difference in temperature can be utilized to produce power. The technology using difference of ocean water temperature is also called as Ocean Thermal Energy Conversion or OTEC. The minimum temperature difference required to produce power is 25 degree Celsius. This technology has not yet developed to the satisfactory levels and will require many more years to be used for the practical applications.