The National Solar Radiation Database Final Report: Fiscal Years 2022-2024

The National Solar Radiation Database (NSRDB) is the leading public source of high-resolution solar resource data in the United States, with more than 400,000 users annually. This database represents the state of the art in the satellite-based estimation of solar resource information and uses a unique physics-based modeling approach that enables improvements in accuracy with the deployment of the next-generation geostationary satellites. Making the highest-quality, state-of-the-art, regularly updated datasets available on a timely basis for users reduces costs of solar deployment by providing accurate information for siting studies and system output prediction and thereby reduces project financing costs and risks. Also, high-resolution information from the NSRDB enables moving beyond the levelized cost of energy when valuing the impact of renewables on the grid. Additionally, the NSRDB enables the integration of large amounts of solar on the grid by providing critical information about solar availability and variability that is used to enhance grid reliability and power quality. In fiscal years 2022-2024, the NSRDB data were updated using the Physical Solar Model (PSM) version 4.0.0, 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 direct normal irradiance (DNI). The updated PSM was used to generate solar radiation data for 2021-2023, including global horizontal irradiance (GHI), DNI, and diffuse horizontal irradiance. 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 the National Oceanic and Atmospheric Administration's Surface Radiation Budget (SURFRAD). According to data for 2019-2023, the NSRDB processed by the latest PSM has a mean bias error within 5% and 8% for the GHI and DNI, respectively. In fiscal years 2025-2027, we will update the NSRDB annually to extend the data to cover the period from 2024-2026. The typical meteorological year (TMY) will also be updated annually to include additional years (2024-2026). Research and development efforts will focus on improving the PSM and enhancing the accuracy of the operational NSRDB product. The model and data will be validated using ground measurements to ensure accuracy. Due to limitations in the current geostationary satellites, the Alaska region has not been included in the NSRDB. To respond to this challenge, we have started collecting high-resolution satellite data that can provide continuous coverage over the area, and we are exploring the feasibility and pathway to extend the NSRDB. We are collaborating with the National Aeronautics and Space Administration Langley Research Center to explore available satellite data and cloud products suitable for extending the NSRDB. Long-term solar radiation data over Alaska will be developed and provided to the public in the next NSRDB update. In addition, the NSRDB website and servers will be upgraded to enable the delivery of the new datasets.