Estimation of solar radiation from the number of sunshine hours

Several expressions have been used to estimate global solar radiation from Asunshine hours for weather stations in Oman, an arid region. These included Aoriginal (linear) and modified (linear-logarithmic) Angstrom Black type Aregression functions, a quadratic function, a power relationship, a power-Atrigonometric equation and one from a new Angstrom-Black type logarithmic Amodel. For the power trigonometric model, the solar altitude of the station was used as additional information for estimating the solar radiation. All the Amodels performed well as estimators of global solar-radiation from sunshine Ahours but the non-linear models were better than the basic linear model. The Apower-trigonometric model estimated the radiation values best. The quadratic Aand linear-logarithmic models are the preferred models when only the relative Asunshine is used. ʹ(ʹ 1999 Elsevier Science Ltd. All rights reserved.