A greater estimate of 70 GW is obtained by Csanady (1988). However, if only a small fraction can be extracted without noticeably disrupting natural ocean circulation, it is unlikely that more than a few gigawatts can be obtained from the ocean current resource in U.S. waters.

The most promising site for the exploitation of strong currents in the North Atlantic is in the Florida Straits. Modeling the flow as if it were in a confined channel would be inappropriate, as the flow takes the form of a jet with weak currents on either side of the strait. Placing turbines in the jet would tend to broaden it, maintaining the volume flux to a first approximation but reducing the current speed. If the reduction in speed is to be no more than 10 percent, then the committee estimates that no more than 20 percent (4 GW) of the 20 GW incident energy flux could be extracted. Allowing for wake losses, drag on supporting structures, and internal turbine and transmission losses, it is unlikely that more than 1 or 2 GW could practically be transmitted to the electricity grid. Additionally, high turbine density in the water column may substantially divert the Florida Current and force the current flow around the Bahamas. This would reduce the local volume flux, creating a practical extractable power that would be even less than 1 or 2 GW. These preliminary estimates need refinement to account for the actual current profile and for stratification effects. The ocean current assessment group should properly account for back effects by simulating total extractable energy using three-dimensional numerical models that include representation of turbine arrays.

The committee also believes that the assessment group needs to further explore and discuss the effects of meandering and seasonal variability of the Florida Current on the extractable power estimate, as the current shows strong meandering and seasonal variability at various frequencies (Johns and Schott, 1987; Lee et al., 1995).12 These aspects of spatial and temporal variability in the resource could potentially limit the placement of MHK devices to narrow regions with consistent flow and could impact the ability to bring ocean current power into the electrical grid. Furthermore, an accurate assessment of the large-scale technical ocean current resource requires consideration of the near-field wake effect near the device.

CONCLUSIONS AND RECOMMENDATIONS

The ocean current resource assessment is valuable because it provides a rough estimate of ocean current power in U.S. coastal waters. However, less time could have been spent looking at the West Coast

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12 Available at http://oceancurrents.rsmas.miami.edu/caribbean/florida.html.



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