The U.S. Department of Energy (DOE) Wind Energy Program's wind resource assessment group, at the National Renewable Energy Laboratory (NREL) in Golden, Colorado, routinely evaluates climatic data sets acquired for use in wind resource assessments. These assessments result in the production of wind resource maps and atlases used by DOE, utilities, and the U.S. wind energy industry.
An important component of NREL's wind resource assessment methodology is the use of available upper- air data to reconstruct detailed vertical wind profiles for a study region. Currently, the most useful set of upper-air data for this type of analysis are archived observations from approximately eighteen hundred rawinsonde and pilot balloon stations worldwide. However, significant uncertainty exists in the accuracy of the reconstructed profiles for many regions. This is due to the irregular horizontal and vertical spatial coverage of the upper-air stations, and limited data at many of these stations. The Reanalysis data set, created by the National Center for Atmospheric Research and the National Centers for Environmental Prediction has the potential to improve the quality of the vertical profiles. Reanalysis data has two major characteristics that improve upon over NREL's current upper-air data set. First, the Reanalysis process used many data sources, plus a dynamic data assimilation model, to create an even distribution of wind, temperature and other meteorological variables on an approximate 200 km grid worldwide. Second, the Reanalysis data assimilation model produces output for 28 vertical levels, including 10 levels in the lowest 3 km of the atmosphere. Reanalysis data also uses a terrain-following coordinate system, ensuring the vertical resolution of the wind information for each grid point is consistent no matter the surface elevation of a particular region.
At present, NREL has purchased 24+ years (1993-1997) of Reanalysis data. This period of record is the same as that in the upper-air observation data set. We plan to generate from the raw Reanalysis assimilation model output (grbsanl files), for the lowest 3 km above ground level, the types of data files used in NREL's upper-air analysis. Each Reanalysis grid point will be treated as if it were a rawinsonde station. An initial evaluation of the usefulness of the Reanalysis data for wind resource assessment will consist of contrasting Reanalysis derived vertical profiles of the wind characteristics to those generated from upper-air observations for comparable locations during the same period. These comparisons will be made in several different climatic areas including polar, mid-latitude, and tropical wind regimes. The paper will discuss the preliminary results of the evaluation and the status of integrating Reanalysis data into NREL's wind resource assessment methodology