The objective of this chapter is to discuss the filters involved in determining the practical resource; how those filters impact the size and spatial distribution of the practical resource; and how DOE might improve MHK resource assessment and development. The committee observes that, as with some other energy resources (see Box 1-3), the difference between the theoretical or technical resource estimates and the practical resource is large, making the practical resource small in a relative sense. While the theoretical (or technical) MHK resource can appear substantial (many tens of gigawatts or more), the practical resource tends to be small in most locations or diffuse in nature. When considering small-scale energy developments (typically less than 10 MW), MHK development may be feasible and valuable in some locations, but utility-scale MHK developments (more than tens or hundreds of megawatts) will involve significant infrastructure, can have substantial environmental impacts, and can potentially conflict with other uses for the same area.

As an example, extracting 1 GW from waves approaching the Washington and Oregon coastlines would probably require the deployment of a line of MHK devices extending at least 100 km parallel to and just off the coast, which could have major impacts all along the coast. Similarly, extracting more than a small fraction of the theoretical 9 GW resource from Cook Inlet’s large tidal range and associated currents would probably require construction of a continuous fence of turbines that would effectively act as a barrage, which could potentially be unacceptable for societal and environmental reasons.

Determining the practical MHK resource will require a comprehensive evaluation of how the resource interacts with social, environmental, regulatory, and economic filters. Some of the assessment groups have already been moving to further evaluate the spatial variation, which has led to selection of far fewer areas that could have potential for in-depth siting studies and/or potential device installation. Part of the siting analysis will include much more detailed modeling of backflow, circulation, and other characteristics that are then calibrated and evaluated with field data. The detailed siting studies are important, because the scale of impacts for MHK development will probably be most significant at a site-specific or local level. As plans progress for any MHK project, developers will need to contend with two types of constraints: the impacts that it could have on the physical and biological environment and the constraints of working in an ocean or a river that has multiple uses and thus multiple management objectives (e.g., social issues, spatial conflicts). These permitting-related issues are in addition to the significant economic investments faced by development of commercial-scale marine renewable energy.

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