The total OTEC resource for the continental United States was 394 TWh/yr, less than 9 percent of the total U.S. resource estimated (Lockheed Martin Mission Systems & Sensors, 2012). The Florida Straits and the East Coast account for 87 percent of the continental U.S. resource. The Gulf of Mexico, which accounts for the other 13 percent, is not a viable source in winter. The continental U.S. resource is very seasonal and limited, and it is unlikely that plant owners would want to operate only part of the year. According to the assessment, Hawaii could generate 143 TWh/yr, the Mariana Islands (including Guam) could generate 137 TWh/yr, and Puerto Rico and the U.S. Virgin Islands could generate 39 TWh/yr (Lockheed Martin Mission Systems & Sensors, 2012). A further focus on these areas where the thermal resource and the societal need coincide would be worthwhile.


The OTEC assessment group’s GIS database provides a visualization tool to identify sites for optimal OTEC plant placement. However, the resource assessment falls short in other ways. The proprietary plant model used does not allow other plant designs to be optimized. Too little information is available on the temporal variability of the thermal resource, with only seasonal averages from two anomalous El Niño/La Niña years available. In addition, too few isotherm depths are available to allow users to optimize the cold-water pipe length.

Recommendation: The OTEC GIS should be modified to display monthly resolution over a longer time period (at least a decade) to allow for evaluation of the thermal resource for the full seasonal cycle as well as for special periods such as El Niño and La Niña. Isotherm depths (at 1°C intervals) should be included in the database so other pipe lengths can be evaluated for OTEC and seawater air conditioning.

The validation effort, which was focused on the plant model instead of the thermal resource represented in their model output, is obviously an issue of great concern. There are plentiful, widely available oceanographic databases available for comparison of the thermal resource. Because the ocean’s thermal stratification is the key input for the OTEC resource assessment, it would have been more useful for the validation to have focused on its representation in the model rather than on a specific plant design.

The group’s estimate of the limit on plant spacing based on cold water supply was also physically unjustified. Instead, the focus should have

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