extractable energy from each of the resource types as called for in the study task statement. To do so would require not only an assessment of the practical resource base discussed by the committee earlier but also an understanding of the relative performance of the technologies that would be used to extract electricity from each resource type. Understanding the performance characteristics of the technologies that might be used to tap these different resources is either just emerging, as is the case for wave and tidal devices, or limited to modeling or sparse pilot plant demonstrations, as is the case for OTEC and ocean currents.
Some comparisons can be made based upon attributes of the different MHK resources, especially their geographical extent and predictability. Clearly, both the ocean current and OTEC resource bases have very limited geographical extent in the United States. The main potential for ocean currents is in the Florida Straits, and the coastal regions of the Hawaiian Islands and Puerto Rico are the most likely places for efficient OTEC siting. In contrast, the resource assessments for waves, tides, and in-stream show a much greater number of locations with substantial resources, though by far the largest location for tidal resources in the United States is in the Cook Inlet of Alaska. Predictability is another important characteristic to consider if a resource is to be incorporated into an electricity system. Tidal resources are highly predictable, with the timing and magnitude of tidal events being known precisely years into the future. In contrast, waves and in-stream resources are related to meteorological conditions that unfold over days and weeks. There is multiday predictability for wave and in-stream systems, especially in settings where the wave spectrum is dominated by swells or in large hydrologic basins, but the predictability is notably less than for tidal systems. The OTEC resource in the United States has little day-to-day variability but, like in-stream, is seasonally dependent. However, location and variability are but two of the many factors that will determine what MHK resources are capable of contributing significantly to power generation in the United States.