SPATIAL AND TEMPORAL VARIABILITY IN THE SOLAR RESOURCE: ASSESSING THE VALUE OF SHORT-TERM MEASUREMENTS AT POTENTIAL SOLAR POWER PLANT SITES

Abstract

The U.S. National Renewable Energy Laboratory (NREL) is responding to a growing demand for high-accuracy solar resource data with uncertainties significantly lower than those of existing solar resource data sets, such as the National Solar Radiation Database (NSRDB). Measurements for long-term solar resource characterizations require years to complete, which is an unacceptable timeline for the rapidly emerging needs of renewable energy applications. NREL has undertaken a collaborative Solar Resource and Meteorological Assessment Project (SOLRMAP) with industry for high-quality ground measurements. To support the SOLRMAP effort, this contribution seeks methods of reducing the uncertainty of existing long-term solar resource data sets by incorporating lower-uncertainty site-specific ground measurements of a limited period of record. In particular, various techniques are being explored to make full use of the existing 10-km resolution radiation data in the NSRDB, and extrapolate them over time using locally measured data and other supportive information. The interannual variability in global and direct radiation is studied here using long-term data at various sites. NSRDB’s modeled data for the 1998‐2005 period are compared to qualitycontrolled measurements to assess the performance of the model, which is found to vary greatly depending on climatic condition. The reported results are encouraging for applications involving concentrators at very sunny sites. Large seasonal biases are found at some cloudy sites. Various improvements are proposed to enhance the quality of the existing model and modeled data.