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Capturing Ocean Heat

Ocean thermal energy conversion offers a timely renewable alternative.

Fortnightly Magazine - October 2009

C (~45 degrees F) is required to produce 5,800 tons of cooling—roughly sufficient to cool 5,800 rooms. Using a 1-meter pipe and about 360 kW of pumping power (compared to 5,000 kW for a conventional AC system) would give an investment payback period of three to four years. 20,21 In the case of a co-located computer server firm, this pay-back period would be considerably shorter since the largest energy costs for these farms are those associated with cooling.

OTEC plants can perform mineral extraction. Most economic analyses show that dissolved mineral extraction from ocean water is prohibitively expensive due to energy requirements to pump the large volume of water needed and to separate the minerals from seawater; however, because OTEC plants already will be pumping the water, the cost of the extraction process is the only remaining factor. Investigations are underway to determine the feasibility of combining the extraction of elements dissolved in seawater with ocean energy production. 22

Like hydroelectric dams, most of the costs of an OTEC plant are up-front—once the infrastructure is in place, the fuel (solar energy) costs are essentially zero, and day-to-day expenses are only those associated with routine operations and maintenance (O&M). 23

OTEC plants offer economic advantages not only on a plant level, but also in terms of the broader economy. Investment in the RD&D for an OTEC infra- structure will create many new employment opportunities, not just directly but also in complimentary and spin-off industries, similar to that seen in the Apollo and Space Shuttle programs. 24

OTEC would reduce, both domestically and globally, dependence on fossil fuels, especially petroleum, of which about half of the world’s proven reserves are located in nations that are sponsors of, or allied with, terrorist groups. 25,26 Thus, while OTEC-generated electricity and liquid fuel side-products won’t eliminate oil usage, its extensive use could impact the financial re-sources of these terrorist groups.

Finally, since OTEC could supply clean and competitively-priced energy globally, engaging in international partnerships to perform the necessary RD&D would help ensure U.S. leadership in ocean, energy, and environmental issues, and could aid in reasserting our influence in the developing nations that was squandered during the past Administration. Further, by working to ensure that developing nations have access to OTEC, this will reduce their need to develop other energy sources, such as nuclear power programs, with their attendant proliferation and accident risks. 27

 

OTEC Challenges

Leaving aside the technical concerns inherent in developing and commercializing any new technologies, there are also several significant challenges to OTEC, not least among them the cost of generating the electricity; on a per-kilowatt-hour basis, OTEC electricity is expensive compared to coal, hydroelectric, and nuclear power. However, as the technology matures, this cost is expected to drop into the range that will make it competitive with technologies that already have very high energy costs.

Additional challenges include low thermodynamic efficiency. The greater the temperature difference between the heat source and a heat sink, the greater the thermal efficiency of an energy-conversion system; however, the small temperature difference between the source (warm