Ocean Thermal Energy Conversion (OTEC) is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient—the fact that the ocean's layers of water have different temperatures to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power, with little impact on the surrounding environment.
The distinctive feature of OTEC energy systems is that the end products include not only energy in the form of electricity, but several other synergistic products. The principle design objective was to minimize plan cost by minimizing plant mass, and taking maximum advantage of minimal warm and cold water flows. Power is converted to high voltage DC, and is cabled to shore for conversion to AC and integration into the local power distribution network.
The oceans are thus a vast renewable energy resource, with the potential to help us produce billions of watts of electric power.
OCEAN THERMAL ENERGY CONVERSION
Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.
INTRODUCTION TO OCEAN ENERGY:
Most people have been witness to the awesome power of the world's oceans. For least a thousand years, scientists and inventors have watched ocean waves explode against coastal shores, felt the pull of ocean tides, and dreamed of harnessing these forces. But it's only been in the last century that scientists and engineers have begun to look at capturing ocean energy to make electricity.
The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves. Ocean thermal energy is used for many applications, including electricity generation. Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are sporadic sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.
OCEAN THERMAL ENERGY CONVERSION:
OTEC is a process which utilizes the heat energy stored in the tropical ocean. The world's oceans serve as a huge collector of heat energy. OTEC plants utilize the difference in temperature between warm surface sea water and cold deep sea water to produce electricity.
The energy associated with OTEC derives from the difference in temperature between two thermal reservoirs. The top layer of the ocean is warmed by the sun to temperatures up to 20 K greater than the seawater near the bottom of the ocean. OTEC energy is different from geothermal energy in that one cannot assume the cold reservoir is infinite. The physical energy of two large reservoirs of fluid at different temperatures is
in J/kg where r is the mass of warm water divided by the mass of cold water entering the plant(1). For optimal performance, r is approximately 0.5. It is assumed in this analysis that the specific heat of the two fluid reservoirs is an average value over the often small temperature difference, but varying with salinity in the case of seawater.
Thermal energy conversion is an energy technology that converts solar radiation to electric power. OTEC systems use the ocean's natural thermal gradient—the fact that the ocean's layers of water have different temperatures—to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C, an OTEC system can produce a significant amount of power. The oceans are thus a vast renewable resource, with the potential to help us produce billions of watts of electric power. This potential is estimated to be about 1013 watts of base load power generation, according to some experts. The cold, deep seawater used in the OTEC process is also rich in nutrients, and it can be used to culture both marine organisms and plant life near the shore or on land. OTEC produce steady, base-load electricity, fresh water, and air-conditioning options.
OTEC requires a temperature difference of about 36 deg F (20 deg C). This temperature difference exists between the surface and deep seawater year round throughout the tropical regions of the world. To produce electricity, we either use a working fluid with a low boiling point (e.g. ammonia) or warm surface sea water, or turn it to vapor by heating it up with warm sea water (ammonia) or de-pressurizing warm seawater. The pressure of the expanding vapor turns a turbine and produces electricity.
OTEC has tremendous potential to supply the world’s energy. It is estimated that, in an annual basis, the amount solar energy absorbed by the oceans is equivalent to atleast 4000 times the amount presently consumed by humans. For an OTEC efficiency of 3 percent, in converting ocean thermal energy to electricity, we would need less than 1 percent of this renewable energy to satisfy all of our desires for energy.
OTEC offers one of the most compassionate power production technologies, since the handling of hazardous substances is limited to the working fluid (e.g., ammonia), and no noxious by-products are generated. Through adequate planning and coordination with the local community, recreational assets near an OTEC site may be enhanced. OTEC is capital-intensive, and the very first plants will most probably be small requiring a substantial capital investment. Given the relatively low cost of crude oil and of fossil fuels in general, the development of OTEC technologies is likely to be promoted by government agencies. Conventional power plants pollute the environment more than an OTEC plant would and, as long as the sun heats the oceans, the fuel for OTEC is unlimited and free.