wave field due to additional wind input (if present) would occur over distances much larger than the spacing between rows of wave energy extraction devices that are currently under consideration. This shadowing effect implies that it is erroneous to estimate the theoretical resource as the sum of the wave power density over an area as one might do for solar energy. Note that the magnitude of this shadowing effect is likely to be highly dependent on the specific characteristics of the device (e.g., size, efficiency). Although there are some initial publications with rigorous analytical approaches for quantifying the effect of an arbitrary array of point absorbers devices (e.g., Garnaud and Mei, 2010), shadowing effects due to realistic devices are a topic of active research. The planning of any potential large-scale deployment of wave power devices would require sophisticated, site-specific field and modeling analysis of the devices’ interactions with the wave field.

One approach to interpreting wave power density maps correctly is to evaluate the wave energy traveling shoreward across a line parallel to the coastline (perhaps located on a bathymetric contour). This is shown in Table 1 as the “total regional wave resource” assessment recommended by the committee. Provided that the selected line is on the continental shelf, it is reasonable to assume that the winds do not add significant energy to the wave field after the waves cross this line. In this case, the wave power density across such a line provides a reasonable approximation to the theoretical resource that represents the wave energy available to nearshore wave energy devices in a region. To do this estimate properly, wave direction information, in addition to the wave frequency spectrum, must be known.

Description of Wave Resource Estimate

The wave resource assessment group was tasked with producing estimates of the theoretical and technical resource in U.S. coastal regimes. In order to obtain estimates of the theoretical wave resource (left column in Figure 1), the wave resource assessment group utilizes a hindcast of wave conditions that was assembled by the National Oceanic and Atmospheric Administration’s (NOAA’s) National Center for Environmental Prediction (NCEP) using its wave-generation and -propagation model WAVEWATCH III. The hindcast generally provides wave parameters over a 4’ x 4’ grid, although the resolution is coarser in a few areas (Alaska, for example, is gridded at 4’ x 8’) (Jacobson et al., 2010). Thus the resolution is generally on the order of many kilometers, whereas the shelf bathymetry can vary rapidly over a few hundred meters. The assessment and validation groups first resolve several potential issues related to the available hindcast (i.e., a short data record of only 51 months, a lack of full spectral



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