What is Ocean Thermal Energy Conversion?
Ocean Thermal Energy Conversion (OTEC) is the process of converting the ocean waters temperature difference at different depths into usable energy. From the solar heated upper depths of the ocean to the cooler depths below 2,000 feet a 40 degree temperature difference must be maintained to generate electricity. This is a relatively new and unheard of source of energy. Many people are not aware of the many benefits of OTEC and the impact it will have in the future as the use of fossil fuel conversion declines. Heightened environmental concerns in today's world makes OTEC an attractive alternative for energy conversion. The ocean offers a natural and renewable resource which will make it possible for converting energy this way to last for a very long, long time. OTEC is a very cost effective method of using the oceans waters for energy conversion but its use and benefits to society have been obscure to the general public. In the coming years OTEC will probably be at the forefront of new energy resources and a good understanding of it know will prove invaluable to power engineers of the future. How does Thermal Energy Conversion Work?
OTEC is a form of solar power in that it uses the sun's energy to heat the upper depths of the oceans waters. Since the sun's energy cannot penetrate very deep depths (approximately 2000ft.) the temperature below these levels is much colder then those near the surface. Most of the solar energy is absorbed in the top layer (35 to 100 m) of water. This upper layer of warm water is very uniformed in temperature because wind and waves cause the water to circulate and mix. The temperature in this layer can reach close to 82° F (28° C ) from regions close the equator. Beyond this layer the temperature drops noticeably with the depth until 800 m to1000 m. At this depth the temperature is 40° F (4.4° C ). From here the temperature changes very gradually. The colder water at these great depths is the result of melting ice in the polar regions. The colder water has a higher density than the warmer water which causes two important events. First the higher density water will sink and displace the lighter, warm water. Secondly, the rotation of the earth forces the heavier cold water to move toward the equator. Because of this, the ocean provides a large reservoir of cold and warm water that can differ in temperature of 40° to 45° F ( 22° to 25° C). This can be seen in the following diagram. There are three basic processes utilized in Ocean Thermal Energy Conversion: Closed-cycle, Open-cycle, and Hybrid-cycle. To give you an ideal of the process, a picture of the open-water cycle is shown below. The closed-cycle process uses a working fluid with a low-boiling point such as ammonia, propane, or Freon. The warm surface water will be used in a heat exchange which will then transfer its heat to the working fluid. When the working fluid vaporizes it propels a turbine to turn a generator which will produce electricity. After the working fluid has been vaporized it is passed through a condenser where cold water from the deeper depths of the ocean is used to convert the vaporized fluid back to a liquid state. The working fluid will now be ready to start the process over again. A picture of the internal workings can be found below. In an open-cycle process the seawater is used as the working fluid unlike the closed-cycle which used a low-boiling point liquid for its working fluid. A near vacuum is used on the surface water which causes it to vaporize. Like the working fluids in the above paragraph the vaporized sea water is used to turn a low pressure turbine which is connected to a generator, thus producing electrical energy. The vaporized surface water is then condensed using the cooler water from deeper in the ocean, then introduced back into the ocean. When the warm surface water is vaporized the salts are left behind thus creating almost pure fresh water. The...
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