Estimation of solar radiation from the number of sunshine hours

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