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Ocean thermal emergy conversion 214


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Ocean thermal emergy conversion 214

  2. 2. ABSTRACT OTEC, or Ocean Thermal Energy Conversion, is an energy technology thatconverts solar radiation to electric power. OTEC systems use the oceans naturalthermal gradient—the fact that the oceans layers of water have different temperatures todrive a power-producing cycle. As long as the temperature between the warm surfacewater and the cold deep water differs by about 20°C (36°F), an OTEC system canproduce a significant amount of power, with little impact on the surroundingenvironment. The distinctive feature of OTEC energy systems is that the end products includenot only energy in the form of electricity, but several other synergistic products. Theprinciple design objective was to minimize plan cost by minimizing plant mass, andtaking maximum advantage of minimal warm and cold water flows. Power is convertedto high voltage DC, and is cabled to shore for conversion to AC and integration into thelocal power distribution network. The oceans are thus a vast renewable resource, with the potential to help usproduce billions of watts of electric power. 2
  3. 3. OCEAN THERMAL ENERGY CONVERSION Oceans cover more than 70% of Earths surface, making them the worlds largestsolar collectors. The suns heat warms the surface water a lot more than the deep oceanwater, and this temperature difference creates thermal energy. Just a small portion of theheat trapped in the ocean could power the world.I. INTRODUCTION TO OCEAN ENERGY: Most people have been witness to the awesome power of the worlds oceans. Forleast a thousand years, scientists and inventors have watched ocean waves explodeagainst coastal shores, felt the pull of ocean tides, and dreamed of harnessing theseforces. But its only been in the last century that scientists and engineers have begun tolook at capturing ocean energy to make electricity. The ocean can produce two types of energy: thermal energy from the suns heat,and mechanical energy from the tides and waves. Ocean thermal energy is used for manyapplications, including electricity generation. Ocean mechanical energy is quite differentfrom ocean thermal energy. Even though the sun affects all ocean activity, tides aredriven primarily by the gravitational pull of the moon, and waves are driven primarily bythe winds. As a result, tides and waves are sporadic sources of energy, while oceanthermal energy is fairly constant. Also, unlike thermal energy, the electricity conversionof both tidal and wave energy usually involves mechanical devices.II. OCEAN THERMAL ENERGY CONVERSION: OTEC or Ocean Thermal Energy Conversion (OTEC) is a process which utilizesthe heat energy stored in the tropical ocean. The worlds oceans serve as a huge collectorof heat energy. OTEC plants utilize the difference in temperature between warm surfacesea water and cold deep sea water to produce electricity. Thermal energy conversion is an energy technology that converts solar radiationto electric power. OTEC systems use the oceans natural thermal gradient—the fact thatthe oceans layers of water have different temperatures—to drive a power-producingcycle. As long as the temperature between the warm surface water and the cold deepwater differs by about 20°C, an OTEC system can produce a significant amount ofpower. The oceans are thus a vast renewable resource, with the potential to help usproduce billions of watts of electric power. This potential is estimated to be about 10 13watts of base load power generation, according to some experts. The cold, deep seawaterused in the OTEC process is also rich in nutrients, and it can be used to culture bothmarine organisms and plant life near the shore or on land. OTEC produce steady, base-load electricity, fresh water, and air-conditioning options. 3
  4. 4. OTEC requires a temperature difference of about 36 deg F (20 deg C). Thistemperature difference exists between the surface and deep seawater year roundthroughout the tropical regions of the world. To produce electricity, we either use aworking fluid with a low boiling point (e.g. ammonia) or warm surface sea water, or turnit to vapor by heating it up with warm sea water (ammonia) or de-pressurizing warmseawater. The pressure of the expanding vapor turns a turbine and produces electricity.Plant Design and LocationCommercial OTEC facilities can be built on • Land or near the shore • Platforms attached to the shelf • Moorings or free-floating facilities in deep ocean water Land-based and near-shore are more advantageous than the other two. OTEC plantscan be mounted to the continental shelf at depths up to 100 meters, however may makeshelf-mounted facilities less desirable and more expensive than their land-basedcounterparts. Floating OTEC facilities with a large power capacity, but has the difficultyof stabilizing and of mooring it in very deep water may create problems with powerdelivery. Commercial ocean thermal energy conversion (OTEC) plants must be located in anenvironment that is stable enough for efficient system operation. The temperature of thewarm surface seawater must differ about 20°C (36°F) from that of the cold deep waterthat is no more than about 1000 meters (3280 feet) below the surface. The natural oceanthermal gradient necessary for OTEC operation is generally found between latitudes 20deg N and 20 deg S. 4