Methodology, Results, and Presentation
The committee benefited from three presentations by the wave resource assessment group2,3,4, and their final report (EPRI, 2011). The committee commented on the work of the assessment group on the basis of these materials and has identified concerns related to the suitability of the hindcast data set in shallow waters, the technique used to generate the aggregate theoretical resource, the lack of directional information, and the technology assumptions utilized for assessment of the total technical resource.
Shallow Water Bathymetry
At a resolution of 4 minutes globally, the WAVEWATCH III simulations cannot capture wave transformation effects due to bathymetric features over shorter spatial scales because the simulations cannot resolve such variability. However, these bathymetric effects are known to be important at depths shallower than approximately 50 m (Dean and Dalrymple, 1984). Shallow-water regions might be of significant interest to developers who seek to optimize the ratio of construction and operating costs to the expected extractable power (largely a function of cable cost/distance to the coast). The methodology used precludes providing site-specific information to such developers. Reliable site-specific information in shallow waters can only be produced using results from models with higher spatial resolution that include the consideration of shallow-water physics (e.g., shoaling, refraction, diffraction). The wave resource assessment group acknowledges that its results are not accurate in the shallower waters of the inner continental shelf, and as such the shallowest water depths analyzed are 50 m (or 20 m on the Atlantic coast, where the continental shelf is smoother and less steep). Areas where inaccuracies due to these bathymetric concerns are most prevalent are blanked out in the GIS. While these regions could be assessed in the future using a shallow-water model such as SWAN, the results of
2 P. Jacobson, Electric Power Research Institute, G. Hagerman, Virginia Tech, and G. Scott, National Renewable Electricity Laboratory, “Assessment and mapping of the U.S. wave energy resource,” Presentation to the committee on November 15, 2010.
3 G. Hagerman, Virginia Tech, and P. Jacobson, Electric Power Research Institute, “Meaning and value of U.S. wave energy resource assessments,” Presentation to the committee on February 8, 2011.
4 G. Hagerman, Virginia Tech, P. Jacobson, Electric Power Research Institute, and G. Scott, National Renewable Energy Laboratory, “Assessment and visualization of United States wave energy resource,” Presentation to the committee on September 27, 2011.