Advancing Radiative Transfer Models for Solar Energy Applications

Radiative transfer models that simulate atmospheric radiation under all-sky conditions have been developed and widely used for weather and climate studies. Compared to those applications, radiative transfer models for solar energy have unique requirements; thus, specific prerequisites are inherent in the model design. For instance, solar resource assessment and forecasting studies require extremely efficient computations of solar radiation over both horizontal and inclined surfaces because photovoltaic (PV) panels frequently track the sun on multiple axes. This work briefly reviews the National Renewable Energy Laboratory’s recent efforts on developing novel radiative transfer models to promote solar energy applications. The Fast All-sky Radiation Model for Solar applications (FARMS) utilizes clear-sky simulations and a parameterization of cloud transmittance and reflectance to rapidly compute broadband irradiances on horizontal surfaces. The accuracy of FARMS is comparable to two-stream approximation, but it is approximately 1,000 times faster. A FARMS for Narrowband Irradiances over Tilted surfaces (FARMS-NIT) has been developed to compute plane-of-array (POA) irradiances in 2,002 narrow wavelength bands. The FARMS-NIT has further been extended for bifacial PV panels that collect solar radiation from both front- and back-sides of the modules. This presentation will focus on the development of FARMS and FARMS-NIT and its validation and applications.