The NSRDB PV Resource Product: Spectral Solar Radiation Data on Inclined Surfaces

Global horizontal irradiance (GHI) and direct normal irradiance (DNI), representing broadband solar radiation measured on a horizontal surface and those received in a narrow beam along the direction of the incoming sunlight, respectively, are the most frequently used quantities to assess the solar resource in specific locations or large-scale areas. However, GHI and DNI indirectly, and often deficiently, represent the amount of radiation that is converted into electric power by photovoltaic (PV) panels that are usually installed at tilt angles or on solar tracking systems to maximize the power output. Spectral distribution of surface radiation, affects the PV performance due to the spectral response of semiconductor materials and the solar cell designs to split spectral radiation, but this information is not directly informed from GHI and DNI data. To address this issue, we developed a Fast All-sky Radiation Model for Solar applications with Narrowband Irradiances on Tilted surfaces (FARMS-NIT) to simultaneously compute spectral radiation over horizontal and inclined surfaces using the physical properties that can be inferred by surface- or satellite-based radiometers. It utilizes the optical properties of aerosols and a pre-computed lookup table of cloud transmittance to efficiently solve spectral radiances that can be spectrally and angularly weighted to directly match the PV response. This new model has been implemented in the National Solar Radiation Data Base (NSRDB) to quantify the solar resource that is available for conversion by a PV plant. The data are referred to as the NSRDB PV Resource product to be distinguished from the routine solar resource product from satellite observations. This study will review the input data and mechanics to develop the PV Resource product as well as the procedures to access the product. To provide a critical reference in the data applications, we will evaluate the PV Resource data using surface observations from stations operated by the National Renewable Energy Laboratory (NREL), University of Oregon, and the First Solar, Inc.