Ocean thermal energy conversion is hydro energy conversion system which uses the temperature difference that exists between deep and shallow waters to run a heat engine. As with any heat engine, the greatest efficiency and power is produced with the largest temperature difference. This temperature difference generally increases with decreasing latitude, i.e. near the equator, in the tropics. Historically, the main technical challenge of OTEC was to generate significant amounts of power, efficiently, from this very small temperature ratio. Changes in efficiency of heat exchange in modern designs allow performance approaching the theoretical maximum efficiency.
The Earths oceans are continually heated by the sun and cover nearly 70% of the Earths surface; this temperature difference contains a vast amount of solar energy which can potentially be harnessed for human use. If this extraction could be made cost effective on a large scale, it could provide a source of renewable energy needed to deal with energy shortages, and other energy problems. The total energy available is one or two orders of magnitude higher than other ocean energy options such as wave power, but the small magnitude of the temperature difference makes energy extraction comparatively difficult and expensive, due to low thermal efficiency. Earlier OTEC systems had an overall efficiency of only 1 to 3% . Current designs under review will operate closer to the theoretical maximum efficiency. The energy carrier, seawater, is free, although it has an access cost associated with the pumping materials and pump energy costs. Although an OTEC plant operates at a low overall efficiency, it can be configured to operate continuously as a Base load power generation system. Any thorough Cost-benefit analysis should include these factors to provide an accurate assessment of performance, efficiency, operational and construction costs and returns on investment.
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