Validating a Physical Model for Satellite Based Solar Resource Assessment

Models to compute Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI) have been in development over the last 3 decades. These models can be classified as empirical or physical based on the approach. Empirical model relate ground based observations with satellite measurements and use these relations to compute surface radiation. Physical models consider the radiation received at the satellite and create retrievals to estimate surface radiation. While empirical methods have been traditionally used for computing surface radiation for the solar energy industry the advent of faster computing has made operational physical models viable. The Global Solar Insolation Project (GSIP) is an operational physical model from NOAA that computes GHI using the visible and infrared channel measurements from the GOES satellites. GSIP uses a two-stage scheme that first retrieves cloud properties and uses those properties in a radiative transfer model to calculate surface radiation. NREL, University of Wisconsin and NOAA have recently collaborated to adapt GSIP to create a 4 km GHI and DNI product every 30 minutes. This paper presents an outline of the methodology and a comprehensive validation using datasets from NREL's Solar Resource and Meteorological Assessment Project (SOLRMAP) and NOAA's Surface Radiation (SURFRAD) Network. Also presented are possible methods to improve the accuracy of the datasets.