A regression model for the beam transmittance of the atmosphere based on data for Shenandoah, Georgia, U.S.A

A model for the beam transmittance of the atmosphere based on the hourly clearness index useful for decomposing hourly global irradiation into beam and diffuse components is presented. The development of the five-year data base for this model which was assembled from observations at the site of the Solar Total Energy Project at Shenandoah, Georgia, is outlined. The five-year model is shown to be preferable to any annual model from a constituent year. The resulting model is shown to be similar to the well-known Randall-Whitson model except in the highest range of clearness indices. Available evidence tends to support a preference for the new model in the region of disagreement.