OTEC has important benefits other than power production.
Air conditioning
The cold (5°C, 41°F) seawater made available by an OTEC system creates an opportunity to provide large amounts of cooling to operations that are related to or close to the plant. The cold seawater delivered to an OTEC plant can be used in chilled-water coils to provide air-conditioning for buildings. It is estimated that a pipe 0.3-meters in diameter can deliver 0.08 cubic meters of water per second. (0.296 cubic meters of water per second or 4700 gallons per minute, is the maximum for a 0.3 meter diameter steel pipe) If 6°C water is received through such a pipe, it could provide more than enough air-conditioning for a large building. If this system operates 8000 hours per year and local electricity sells for 5¢-10¢ per kilowatt-hour, it would save $200,000-$400,000 in energy bills annually (U.S. Department of Energy, 1989).
The InterContinental Resort and Thalasso-Spa on the island of Bora Bora uses an OTEC system to air-condition its buildings. The system accomplishes this by passing cold seawater through a heat exchanger where it cools freshwater in a closed loop system. This cool freshwater is then pumped to buildings and is used for cooling directly (no conversion to electricity takes place).
The InterContinental Resort and Thalasso-Spa on the island of Bora Bora uses an OTEC system to air-condition its buildings. The system accomplishes this by passing cold seawater through a heat exchanger where it cools freshwater in a closed loop system. This cool freshwater is then pumped to buildings and is used for cooling directly (no conversion to electricity takes place).
Chilled-soil agriculture
OTEC technology also supports chilled-soil agriculture. When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics. The Common Heritage Corporation, a former tenant at the Natural Energy Laboratory, and the holder of the patent on this process, maintained a demonstration garden with more than 100 different fruits and vegetables, many of which would not normally survive in Hawaii. No chilled soil agriculture is presently being undertaken at the Natural Energy Laboratory.
Aquaculture
Aquaculture is the most well-known byproduct of OTEC. It is widely considered to be one of the most important ways to reduce the financial and energy costs of pumping large volumes of water from the deep ocean. Deep ocean water contains high concentrations of essential nutrients that are depleted in surface waters due to biological consumption. This "artificial upwelling" mimics the natural upwellings that are responsible for fertilizing and supporting the world's largest marine ecosystems, and the largest densities of life on the planet.
Cold-water delicacies, such as salmon and lobster, thrive in the nutrient-rich, deep, seawater from the OTEC process. Microalgae such as Spirulina, a health food supplement, also can be cultivated in the nutrient rich water. Because the OTEC process uses cold, deep-ocean water and warm ocean water from the surface, it can be combined in various ratios to deliver sea water of a specific temperature conducive to maintaining an optimal environment for aquaculture. For example, Maine lobster could be grown in a tropical island environment in a temperature controlled mixture of cold and warm sea water.
Seafood not indigenous to tropical waters, can also be raised in pools created by OTEC-pumped water, such as Salmon, lobster, abalone, trout, oysters, and clams. This extends the variety of fresh seafood products available for nearby markets. Likewise, the low-cost refrigeration provided by the cold seawater can be used to upgrade or maintain the quality of indigenous fish, which tend to deteriorate quickly in warm tropical regions.
Desalination
Desalinated water can be produced in open- or hybrid-cycle plants using surface condensers. In a surface condenser, the spent steam is condensed by indirect contact with the cold seawater. This condensate is relatively free of impurities and can be collected and dispensed to local communities where supplies of natural freshwater for agriculture or drinking are limited. System analysis indicates that a 2-megawatt (electric) (net) plant could produce about 4300 cubic meters of desalinated water each day (Block and Lalenzuela 1985).
Hydrogen production
Hydrogen can be produced via electrolysis using electricity generated by the OTEC process. The steam generated can be used as a relatively pure medium for electrolysis with electrolyte compounds added to improve the overall efficiency. OTEC technology can be scaled to generate large quantities of hydrogen which can supply the burgeoning global marketplace. OTEC installations on islands, platforms, barges and ships have the potential for large scale, global hydrogen generation with supply to major ports via hydrogen tanker ships. For example, this is the method of delivery currently used to transport hydrogen to the Kennedy Space Center for use by NASA. The main challenges include the cost of production, transportation, and distribution, relative to other energy sources and fuels. Considering the increasing price of petroleum products on world markets, costs for large scale hydrogen production and distribution could be subject to change in a relatively small amount of time.
Mineral extraction
Another undeveloped opportunity, is the potential to mine ocean water for its 57 elements contained in salts and other forms and dissolved in solution. In the past, most economic analyses concluded that mining the ocean for trace elements dissolved in solution would be unprofitable, in part because much energy is required to pump the large volume of water needed. More significantly, it is often very expensive to separate the minerals from seawater. Generally this method is limited to minerals that occur in high concentrations, and can be extracted easily, such as magnesium.
However, with OTEC plants supplying the pumped water, the remaining problem is the cost of the extraction process. The Japanese recently began investigating the concept of combining the extraction of uranium dissolved in seawater with wave-energy technology. They found developments in other technologies (especially materials sciences) were improving the viability of mineral extraction processes that employ ocean energy.
Political concerns
Because OTEC facilities are more-or-less stationary surface platforms, their exact location and legal status may be affected by the United Nations Convention on the Law of the Sea treaty (UNCLOS). This treaty grants coastal nations 3-, 12-, and 200-mile zones of varying legal authority from land, creating potential conflicts and regulatory barriers to OTEC plant construction and ownership. OTEC plants and similar structures would be considered artificial islands under the treaty, giving them no legal authority of their own. OTEC plants could be perceived as either a threat or potential partner to fisheries management or to future seabed mining operations controlled by the International Seabed Authority.
Cost and economics
For OTEC to be viable as a power source in terms of global utilization, the technology must have equal tax and subsidy treatment as competing energy sources. Because OTEC systems have not yet been widely deployed, estimates of their costs are uncertain. One study estimates power generation costs as low as US $0.07 per kilowatt-hour, compared with $0.07 for subsidized wind systems.
Beneficial factors that should be taken into account include OTEC's status as a renewable resource (with no combustion or waste products or limited fuel supply), the amount of area in which it is available, (often within 20° of the equator) the geopolitical effects of dependence and reliance on petroleum, the development of alternate forms of ocean power such as wave energy, tidal energy and methane hydrates, and the possibility of combining it with solar energy, aquaculture, refrigeration and air conditioning, hydrogen production or filtration for trace minerals to obtain multiple uses from a single pump system.
OTEC technology also supports chilled-soil agriculture. When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics. The Common Heritage Corporation, a former tenant at the Natural Energy Laboratory, and the holder of the patent on this process, maintained a demonstration garden with more than 100 different fruits and vegetables, many of which would not normally survive in Hawaii. No chilled soil agriculture is presently being undertaken at the Natural Energy Laboratory.
Aquaculture
Aquaculture is the most well-known byproduct of OTEC. It is widely considered to be one of the most important ways to reduce the financial and energy costs of pumping large volumes of water from the deep ocean. Deep ocean water contains high concentrations of essential nutrients that are depleted in surface waters due to biological consumption. This "artificial upwelling" mimics the natural upwellings that are responsible for fertilizing and supporting the world's largest marine ecosystems, and the largest densities of life on the planet.
Cold-water delicacies, such as salmon and lobster, thrive in the nutrient-rich, deep, seawater from the OTEC process. Microalgae such as Spirulina, a health food supplement, also can be cultivated in the nutrient rich water. Because the OTEC process uses cold, deep-ocean water and warm ocean water from the surface, it can be combined in various ratios to deliver sea water of a specific temperature conducive to maintaining an optimal environment for aquaculture. For example, Maine lobster could be grown in a tropical island environment in a temperature controlled mixture of cold and warm sea water.
Seafood not indigenous to tropical waters, can also be raised in pools created by OTEC-pumped water, such as Salmon, lobster, abalone, trout, oysters, and clams. This extends the variety of fresh seafood products available for nearby markets. Likewise, the low-cost refrigeration provided by the cold seawater can be used to upgrade or maintain the quality of indigenous fish, which tend to deteriorate quickly in warm tropical regions.
Desalination
Desalinated water can be produced in open- or hybrid-cycle plants using surface condensers. In a surface condenser, the spent steam is condensed by indirect contact with the cold seawater. This condensate is relatively free of impurities and can be collected and dispensed to local communities where supplies of natural freshwater for agriculture or drinking are limited. System analysis indicates that a 2-megawatt (electric) (net) plant could produce about 4300 cubic meters of desalinated water each day (Block and Lalenzuela 1985).
Hydrogen production
Hydrogen can be produced via electrolysis using electricity generated by the OTEC process. The steam generated can be used as a relatively pure medium for electrolysis with electrolyte compounds added to improve the overall efficiency. OTEC technology can be scaled to generate large quantities of hydrogen which can supply the burgeoning global marketplace. OTEC installations on islands, platforms, barges and ships have the potential for large scale, global hydrogen generation with supply to major ports via hydrogen tanker ships. For example, this is the method of delivery currently used to transport hydrogen to the Kennedy Space Center for use by NASA. The main challenges include the cost of production, transportation, and distribution, relative to other energy sources and fuels. Considering the increasing price of petroleum products on world markets, costs for large scale hydrogen production and distribution could be subject to change in a relatively small amount of time.
Mineral extraction
Another undeveloped opportunity, is the potential to mine ocean water for its 57 elements contained in salts and other forms and dissolved in solution. In the past, most economic analyses concluded that mining the ocean for trace elements dissolved in solution would be unprofitable, in part because much energy is required to pump the large volume of water needed. More significantly, it is often very expensive to separate the minerals from seawater. Generally this method is limited to minerals that occur in high concentrations, and can be extracted easily, such as magnesium.
However, with OTEC plants supplying the pumped water, the remaining problem is the cost of the extraction process. The Japanese recently began investigating the concept of combining the extraction of uranium dissolved in seawater with wave-energy technology. They found developments in other technologies (especially materials sciences) were improving the viability of mineral extraction processes that employ ocean energy.
Political concerns
Because OTEC facilities are more-or-less stationary surface platforms, their exact location and legal status may be affected by the United Nations Convention on the Law of the Sea treaty (UNCLOS). This treaty grants coastal nations 3-, 12-, and 200-mile zones of varying legal authority from land, creating potential conflicts and regulatory barriers to OTEC plant construction and ownership. OTEC plants and similar structures would be considered artificial islands under the treaty, giving them no legal authority of their own. OTEC plants could be perceived as either a threat or potential partner to fisheries management or to future seabed mining operations controlled by the International Seabed Authority.
Cost and economics
For OTEC to be viable as a power source in terms of global utilization, the technology must have equal tax and subsidy treatment as competing energy sources. Because OTEC systems have not yet been widely deployed, estimates of their costs are uncertain. One study estimates power generation costs as low as US $0.07 per kilowatt-hour, compared with $0.07 for subsidized wind systems.
Beneficial factors that should be taken into account include OTEC's status as a renewable resource (with no combustion or waste products or limited fuel supply), the amount of area in which it is available, (often within 20° of the equator) the geopolitical effects of dependence and reliance on petroleum, the development of alternate forms of ocean power such as wave energy, tidal energy and methane hydrates, and the possibility of combining it with solar energy, aquaculture, refrigeration and air conditioning, hydrogen production or filtration for trace minerals to obtain multiple uses from a single pump system.
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