The oceans cover a little more than 70 percent of the earth surface. This makes it the worlds largest solar energy collector and energy storage system. On an average day, 60 million square kilometers if tropical seas absorb and amount of solar radiation equal in heat content to about 250 million barrels of oil. The history of mankind, have depended upon its ability to conquer the forces of nature, and to utilize these forces to serve its needs. Energy technology is certainly one of the most important factors in the emergence of mankind as the dominant species of this plant. The invention of the practical steam engine by James watt, brought about development of large factories, steam ships and the steam locomotive. First wood was used, then coal. About the same time, the use of coal instigated advances in metallurgy .petroleum from natural seepage has been used since ancient times for lighting, lubrication and waterproofing. The introduction of drilling for oil greatly increased the supply of oil. The industrial revolution switches in to high gear. One problem is that the natural seepage is limited and in a few years the elements will be used. The development of nuclear power was touted as the answers to all mankind’s energy woes. It not turned out that way. The elimination of government subsidies for nuclear power plants has made them quite unaffordable. When it went so bad no insure in the world will write disaster for nuclear power plant
The concept of OTEC (ocean thermal energy conversion) has existed for over a century as fantasised by Jules Verne in 1870 and conceptualised by French physicist, Jacques arsene d arsonval in 1881. Despite this an operating OTEC power facility was not developed until the 1920’s.
2.2 WHAT IS OTEC
OTEC, ocean thermal energy conversion is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean’s natural thermal gradient, consequently the temperature difference between the warm surface water and the cold deep water below 600 metres by about 20’c, an OTEC system can produce, a significantly amount of power. The oceans are thus a vast renewable resource; with the potential to help us in the OTEC process is also rich in nutrients and it can be used to culture both marine organism and plant life near the shore or on land

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The total influx of solar energy into earth is of thousands of time as a great as mankind total energy use. All of our coal, oil and natural gas are the result of the capture of solar energy by life of the past. There have been, any projects for harnessing solar energy, but most have not been successful because they attempt to capture the energy directly. The idea behind OTEC is the use of all a natural collectors, the se, instead of artificial collector.
2.3 HOW OTEC WORKS
Warm water is collected on the surface of the tropical ocean and pumped by a warm water pump. The water is pumped through the boiler, where some of the water is used to heat the working fluid, usually propane or some similar material. The propane vapour expands through a turbine which is coupled to a generator that generating electric power. Cold water from the bottom is pumped through the condenser, where the vapour returns to the liquid state. The fluid is pumped back into the boiler. Some small fraction of the power from the turbine is used to pump the water through the system and to power other internal operations, but most of it is available as net power.
There are two different kinds of OTEC power plants, the land based and the floating plant. First, land based power plants, the land based pilot plant will consist of a building. This building will contain the heat exchangers, turbines, generators and controls. It will be connected to the ocean via several pipes, and an enormous fish farm (100 football areas) by other pipes. Warm water is collected through a screened enclosure close to the store. A long pipe laid on the slope collects cold water. Power and fresh water are generated in the building by the equipment. Used water if first circulated in to the marine culture pond (fish farm) and then discharges by the third pipe in to the ocean, downstream from the warm water inlet. This is done so that the outflow does not reenter the plan, since re use of warm water would lower the available temperature difference. While, the other OTEC power plants is floating power plants, the floating power plant works in the same way as the land based the apparent different is that the floating plant is floating.
Where actually OTEC can be used, OTEC can be sited anywhere across about 60 million squares kilometres of tropical oceans anywhere there is deep cold water lying under warm surface water this generally means between the tropic of cancer and the tropic of Capricorn. Surface water is these regions, warmed by the sun, generally stys at 25 degrees Celsius or above. Ocean water more than 1000 meters below the surface is generally at about 4 degrees C.
2.4 TYPES OF OTEC
There are three types of OTEC designs: open cycle, closed cycle and hybrid cycle.
Closed cycle
Closed cycle systems use fluid with a low boiling point, such as ammonia, to rotate a turbine to generate electricity. Here how it works. Warm surface sea water is pumped through a heat exchanger where the low boiling water point is vaporized. The expanding vapour turns the turbo generator, then clod, deep seawater pumped through a second heat exchanger condenses the vapour back into a liquid, which is then recycle through the system
Open cycle
Open cycle OTEC uses the tropical oceans warm surface water to make electricity. When warm seawater is placed in a low pressure container, it boils. The expanding steam drives a low pressure turbine attached to an electrical generator. The steam, which has left its slat behind in the low pressure container, is almost pure fresh water. It is condensed back into a liquid by exposure to cold temperature from deep oceans water
Hybrid cycle
Hybrid system combines the feature of both the closed cycle an open cycle system. In a hybrid system, warm seawater enters a vacuum chamber where it is flash evaporated into steam, similar to the open cycle evaporation process. The steam vaporizes a low boiling point fluid that drives a turbine to produce electricity
2.5 ADVANTAGES AND DISADVANTAGES OF OTEC
The advantages of OTEC is the uses OF OTEC is clean, renewable, its natural resource. Warm surface seawater and cold water from the ocean depths replace fossil fuels to produce electricity. Second, its suitably designed OTEC plants will produce little or no carbon dioxide or other pollutant chemical
Third, OTEC system can produce fresh water as well as electricity. This is a significant adapted in island areas where fresh water is limited, other there is enough solar energy received and stored in the warm tropical ocean’s surface layer to provide most, if not all, of present human energy needs and last the use of OTEC as a source of electricity will help reduce the state almost complete dependence on imported fossil fuels.
The disadvantages of OTEC is produced electric at present would cost more than electricity generated from fossil fuels at theirs current costs. Second, OTEC plants must be located were a difference of about 20;c occurs year round. Ocean depths must be available fairly close to shore based facilities for economics operation. Floating plant ships could provide more flexibility. Third, there is no energy company will put money in this project because it only has been tested in very smell scale and last, the construction of OTEC plants and lying of pipes in coastal water may cause localised damage to reefs and near shore marine ecosystems.
2.6 ENVIRONMENTAL IMPACTS OF OTEC
OTEC systems are, for the most part, environmentally benign. Although accidental leakage of closed cycle working fluids can pose a hazard, under normal conditions, the only effluents are the mixed seawater discharges and dissolved gases that come out of solution when sea water is depressurized. Although the quantities of outgassed species may be significant for large OTEC systems, with the exception of carbon dioxide, these species are benign. Carbon dioxide is a greenhouse gas and can impact global climate; however, OTEC systems release one or two orders of magnitude less carbon dioxide than comparable fossil fuel power plants and those emissions may be sequestered easily in the ocean or used to stimulate marine biomass production. OTEC mixed seawater discharges will be at lower temperatures than sea water at the ocean surface. The discharges will also contain high concentrations of nutrients brought up with the deep sea water and may have a different salinity. It is important; therefore, that release back into the ocean is conducted in a manner that minimizes unintended changes to the ocean mixed layer biota and avoids inducing long-term surface temperature anomalies. Analyses of OTEC effluent plumes suggest that discharge at depths of 50-100 m should be sufficient to ensure minimal impact on the ocean environment. Conversely, the nutrient-rich OTEC discharges could be exploited to sustain open-ocean Mari culture