Methodology for Estimating Worldwide Solar Radiation Resources

Under the auspices of the U.S. Department of Energy's Resource Assessment Program, the National Renewable Energy Laboratory (NREL) is developing a methodology for producing solar radiation data grids. A data grid is a framework of uniformly spaced locations (grid points) for which data are available. For example, a solar radiation data grid will likely contain monthly averages of direct normal,diffuse horizontal, and global horizontal daily-total solar radiation energy in units of megajoules per square meter (MJ/m2) or kilowatt-hours per square meter (kWh/m2). The data grid could also contain other statistics such as interannual variability, diurnal variability, and cumulative frequency distributions. Results to date include the development of a model for estimating monthly meandaily-total solar radiation and the acquisition of worldwide data for most of the required input parameters. Aerosol optical depth is the one input parameter for which data are very limited. NREL currently has the ability to generate data grids (40 km spacing) with monthly mean solar resource information for any country or region in the world. Plans have been made to improve this technologyduring the next several years.