information at all grid points), and then move on to an estimation of wave power density near the U.S. coastline. To produce maps of wave power density, the assessment group computes a sum of the power density associated with all wave components at a given location, regardless of wave direction. This is equivalent to considering the wave energy flux (power density) impinging on a cylinder of unit diameter that extends over the entire water column. Its estimate of the total theoretical resource is then computed by lining such cylinders along an entire line of interest (e.g., a 50 m depth contour or a 50 nautical mile line) and summing the wave energy flux over all of these cylinders. The several ramifications of this definition are discussed in the next subsection.
To produce an estimate of the technical wave resource (center column, Figure 1), the wave resource assessment group adopts an approach based on analyzing the cumulative probability density function (PDF) of wave power as a function of wave height. For a given threshold operating condition (TOC) and maximum operating condition (MOC), the percentage of the wave power that can be recovered can be estimated as a function of the rated operating condition (ROC). Note that this approach considers several extraction filters (e.g., cut-in/cut-out constraints) and simplifies or neglects others (e.g., efficiencies, back effects, spacing). The group plans to generate cumulative PDFs for the sites along the U.S. coastline and to estimate the technical wave resource using the TOC and MOC values specific to three devices (Archimedes Wave Swing, Pelamis, and Wave Dragon) for various values of the ROCs.
The products of the wave resource assessment will include a database of 51-month time series at 3 hr intervals of wave parameters that can be used to reconstruct the frequency spectra, although directional spreading information is not available. In addition, the group will provide maps of annual and monthly average wave conditions (i.e., wave power density, wave height, period, direction) in a GIS format. It will use ArcIMS, which is also the GIS web-based platform for the maps in National Renewable Energy Laboratory’s Renewable Resource Data Center. Bulk numbers for the total available theoretical wave resource and the total technical resource for different regions and for the entire United States will also be produced.
Comments on Methodology and Presentation of Results
The committee benefited from two presentations by the wave resource assessment group (Jacobson et al., 2010; Hagerman and Jacobson, 2011) and had access to portions of the group’s final report (EPRI, 2010; Virginia Tech University, 2010; EPRI, 2011). The committee therefore reviewed the work of the assessment group on the basis of these materials and identified