The NREL validation only examined average wave power estimates produced by the assessment group and did not address the validity of the spectral reconstruction.6 The committee found that the validation was generally lacking in rigor, especially given the paucity of available data. The 44 observational locations were insufficient relative to the gradients in power density shown in the assessment, with order of magnitude changes in power density between some locations without validation. More important, no skill metrics were given.
While little can be done to address this shortcoming in the near term, data from the Northeast Regional Association for Coastal Ocean Observing System,7 Scripps Institution of Oceanography’s Coastal Data Information Program buoys,8 and the network of the National Federation of Regional Associations for Coastal and Ocean Observing9 could be used to provide additional validation information in the future.
Perhaps more important, the NREL validation group calculated wave power using a simplified formulation that is valid only in deep water, while the wave resource assessment group used the full reconstructed spectrum for this estimate. Finally, the validation effort did not report any statistical measures that would quantify the agreement between observations and estimates, such as root-mean-square error values, R2 statistics, and the like.
The wave resource assessment, especially the GIS visualization, could prove useful to developers who are interested in identifying general regions for their particular wave energy conversion devices. However, the spatial resolution of the assessment is of necessity very coarse, and there are numerous extraction and practical filters that will likely dominate the actual development of marine and hydrokinetic resources. Site-specific analysis for wave-energy facilities will still be needed at candidate locations. Additional information about the potential temporal variability of electricity generation would also be needed for electricity system operators to integrate wave power into utility-scale electricity systems.
The theoretical wave resource assessment estimates are reasonable, especially for mapping wave power density, although the accepted unit-circle approach overestimates the aggregate total theoretical resource.
6 G. Scott, National Renewable Energy Laboratory. “Validation and display of wave energy resource estimates,” Presentation to the committee on February 8, 2010.