Solar spectral irradiance under clear and cloudy skies: measurements and a semiempirical model

Abstract

To investigate how the spectral transmission of clouds deviates from an assumed neutral density filter, the measured spectra are compared with simulated clear-sky spectra. A correlation is established between the cloud thickness and the relatively higher transmission of clouds in the ultraviolet and blue region of the solar spectrum. Using this approach, a semiempirical model is proposed based solely on global and diffuse broadband irradiance measurements, precipitable water-vapor data, and the sun's position. The model, called SEDES1, is applied to calculate spectral irradiance in short time steps (30 or 60 minutes) that are needed for either the design and performance analysis of spectrally selective solar energy conversion systems or to predict daylight availability. -from Authors