4.2 Mesoscale Modeling as a Tool for Wind Resource Assessment and Mapping

The rapid growth of the wind energy industry in the past decade, both in the United States and elsewhere, has led to the development of new techniques for the systematic identification and evaluation of candidate wind project sites. One of those techniques is mesoscale modeling. A familiar tool of weather forecasting, mesoscale modeling offers a number of advantages for wind resource assessment, such as the ability to simulate, with reasonable accuracy, complex wind flows in areas where surface measurements are scant or non-existent. TrueWind Solutions has developed one such mesoscale modeling technique, which is marketed under the trademark MesoMap. MesoMap has been used in the past five years to create wind resource maps of about half of the United States as well as other parts of the world. Through TrueWind’s internal efforts and a public/private partnership with the National Renewable Energy Laboratory (NREL), the accuracy of the method has been assessed by comparing estimates with data from nearly 1000 surface stations. The typical root-mean-square model error, after accounting for uncertainty in the data, has been found to be 5-7% of the mean speed at 50 m. This is a useful level of accuracy, but improvements are still desirable because of the cubic relationship between the energy available in the wind and speed. The intensive validation effort has identified several common sources of model error. This paper discusses three of the most important: surface roughness parameterization, atmospheric stability in the lower boundary layer, and the mesoscale model resolution. Strategies for researching and mitigating these issues are discussed.