HYCOM model, which would have better paralleled the other resource assessment efforts.

Estimate of Available OTEC Power

There are many interesting physics, chemistry, and biology problems associated with the operation of an OTEC plant. Whitehead and Gershenfeld (1981) suggested that an optimal plant size would be around 100 MW in order to avoid adverse effects on the thermal structure the plant is designed to exploit. The ultimate size of the OTEC resource itself is an interesting question and an issue which has been discussed in both old (Isaacs and Schmitt, 1980) and new literature (Nihous, 2005; 2007a; 2007b). Previous work yielded a wide range of estimates for the global OTEC resource of between 3 TW and 1,000 TW (Nihous, 2005 and references therein), which compares favorably to the current global energy consumption of about 16 TW (IEA, 2011). If the committee uses its own estimate of the power density of ∼500 kW/(m3/s) of cold water upwelling, then a total added upwelling of 10 Sv5 is equivalent to a total power of 5 TW, in agreement with Nihous (2007a). This would represent a 100-MW plant spaced approximately every 50 km in the tropical ocean. While this suggests that OTEC is a very substantial ocean energy source, the many technical and environmental obstacles to its deployment, especially the challenge of utilizing the power produced at sea, means that this concept is still quite far from such large-scale implementation.

The GIS created by the OTEC assessment group was a good way to visually identify sites that might be optimal for OTEC plant placement. However, despite the large global potential, the U.S. OTEC resource estimate provided by the assessment group seems unrealistically high. The assessment group arrives at a figure of 4,642 TWh/yr for the United States, but the majority of the resource is found near Micronesia (1,134 TWh/yr) and Samoa (1,331 TWh/yr) (Lockheed Martin Mission Systems & Sensors, 2012). Unfortunately, there is a serious mismatch between the supply and demand at those locations, as low population densities and levels of industrialization will not create a market for the electricity produced through OTEC. In addition, the 200-mile Exclusive Economic Zone was used as a limit for energy production. This does not fully address the DOE funding opportunity, which requested a discussion of both “resources available with near-shore, grid-connected ocean thermal energy systems and those requir[ing] floating offshore systems” (DOE, 2009). A more realistic limit would be needed to address nearshore options.

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5 A sverdrup (Sv) is a unit of volume transport used in physical oceanography, equivalent



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