Improving the National Solar Radiation Data Base using PSM V4

The National Solar Radiation Database (NSRDB) provides comprehensive global solar resource data at a high temporal and spatial resolution. The NSRDB employs satellite-based solar modeling to retrieve cloud properties and subsequently compute solar radiation. The other input parameters - including aerosol optical properties, precipitable water vapor, surface albedo, temperature, and pressure - are also employed by the model. The NSRDB data were recently updated using physical solar model (PSM) version 4, which includes an improved gap-filling algorithm, based on machine-learning techniques, for the missing cloud properties, corrections of solar position calculations, an enhanced algorithm for computing land-surface albedo over snow or ice surfaces, and a physics-based model for computing DNI. The updated PSM was used to generate solar radiation data for 2021-2023, including global horizontal irradiance (GHI), direct normal irradiance (DNI), and diffuse horizontal irradiance (DHI). This model was also employed to reprocess all previous NSRDB data from 1998-2020. The NSRDB was validated using high-quality measurements from surface sites, including NOAA's the Surface Radiation Budget (SURFRAD). According to data for 2019-2023, the NSRDB processed by the latest PSM has mean bias error (MBE) within 5% and 8%, respectively, for GHI and DNI. This study provides users with the latest NSRDB information and outlines plans for ongoing development and updates.