Ocean Thermal Power History and Arguments For and Against Part 2

About the arguments for and against the use of ocean thermal power as well as history and development of the alternative energy source.


OTP plants could also be used as manufacturing sites for making certain energy-intensive materials, such as aluminum, magnesium, or ammonia, which is in demand for fertilizer and for many other chemical uses. OTP technology is particularly suited to ammonia synthesis, because ammonia essentially can be made from air and seawater. The OTP plant would produce hydrogen from seawater by electrolysis, and then would combine the hydrogen with nitrogen from the air to make ammonia (NH3). Substantial amounts of external raw materials would not be needed, except for catalysts, electrolytes, and replacement electrodes. According to a recent study, it would take just three to four years for the value of the ammonia produced by a 500-megawatt plant to equal the capital invested in the plant.


Although the prospects are apparently good that large OTP plants can be built at costs competitive with nuclear power plants, OTP is still an expensive, highly centralized, capital-intensive technology which will leave consumers dependent on large corporations for power. By contrast, electricity from solar cells will eventually enable customers to own and operate their own minielectric power plants on their rooftops.

Another, more basic problem is that the tropical OTP resource is not ideally situated to supply power to the U.S. The best sites for OTP plants are far from the U.S. in tropical oceans where water temperature gradients are largest and where the oceans are relatively calm. To provide electricity to the U.S., OTP plants might have to be located much farther north in the Gulf of Mexico near the southeastern U.S., or off Puerto Rico, or off Hawaii. But near the southeastern U.S., the water is cooler than in the tropics and the plants would be less efficient; also, strong currents and frequent hurricanes would make stable mooring a problem there.

Although no fundamentally new technology is required for OTP, some engineering problems remain. Very large pipes, up to 4,000 ft. in length, would have to be deployed in the ocean for some OTP designs. Also, not much is known about possible environmental effects of OTP operations resulting from the cooling of the ocean's surface and the mixing of the plant's cold-water discharge plume with warmer subsurface layers. Even a small (100-megawatt) plant would ingest 8 million gallons of cold water per minute and discharge it near the surface. Certain forms of marine life might be adversely affected, and large numbers of OTP plants might even have a perceptible effect on the climate. In addition, some damage would probably occur to marine life sucked into the plant, buffeted by its exhaust stream, or prone to thermal shock from its cold-water outlet.

Whereas an OTP plant designed for electrical generation would be basically pollution-free in normal operation, propane or ammonia could be spilled in an accident or during routine maintenance. Ammonia is very toxic, and propane would present an explosion hazard. The plants might also regularly discharge chlorine used in preventing biofouling of heat-exchanger surfaces, and copper from condensers also could leach into the water with adverse environmental effect.


No OTP plants are currently operating, but the U.S. is planning to build a small pilot plant by the late 1980s. In addition to producing power, OTP plants may one day also be used to create fresh water for irrigation in arid regions, and other plants may produce liquid hydrogen for use as an energy source on shore.

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