Modelling solar data

The objective of this paper is to present validated mathematical models for estimation of hourly and daily solar irradiation on surfaces of arbitrary orientation and tilt from irradiation on a horizontal plane. Daily irradiation on a surface may still be estimated even if only the hours of sunshine are known. To do this regression equations have been established to estimate the hourly or daily diffuse irradiation, given the corresponding horizontal global irradiation. The sky-diffuse irradiation is treated anisotropically and a semi-empirical model is established which treats the surfaces in shade and sunlit surfaces under overcast and non-overcast skies separately. The work presented here is the result of a three-year programme related to modelling of solar data.