A test of Suehrcke’s sunshine–radiation relationship using a global data set

Abstract

In this paper we investigate a new relationship between duration of sunshine and solar radiation on the earth’s surface that was derived recently by Suehrcke (Solar Energy, 68(5) (2000) 417). We test the relationship using over 70,000 measured monthly sunshine and radiation data from nearly 700 sites compiled by the World Radiation Data Center. We show that Suehrcke’s equation accounts adequately for the sunshine–radiation relationship on an average sense. There is a large dispersion (12% on average) in the values of solar radiation calculated by the new equation, however it is unclear how much of this dispersion could be accounted for by a better model. The predictive capabilities of the new model are actually roughly equivalent to those of older models such as Ångström–Prescott when the peculiarities of local climatic conditions are not taken into account.