Enhanced δ-two-stream approximation model of diffuse solar radiation and its application to computation of solar irradiation on tilted surfaces

摘要

This paper presents an enhanced approximate model for computation of atmospheric radiative transfer. That model can be used for computing the solar irradiation on tilted surfaces, a current problem for many purposes and in particular for solar power installations design. The present model takes into consideration one term more than the classical δ-Eddington two-stream model in the spherical harmonics decomposition of atmospheric diffuse radiance. This makes possible a better description of the radiance near the horizon. Despite that extension, due to an additional constraint, the radiance expression results in a sum of only three exponential function of altitude, as in the original δ-Eddington two-stream model. Using that result as the source term of the diffuse radiance equation, an even better solution is easily obtained as it is easy to integrate exponential functions. Comparison is achieved with irradiance experimental values and with an empirical expression of the radiance, both extracted from the literature.