Data bank Comparison of monthly mean hourly sunshine fraction estimation techniques from calculated diffuse radiation values

Mean monthly hourly values of global I and diffuse radiation Id, along with mean monthly daily values of the sunshine fraction σd available for four locations in the United Kingdom, are used to develop six models relating Id/I with the monthly mean hourly clearness index Kt, the estimated monthly mean hourly sunshine fraction σh and the monthly mean solar elevation at mid hour α. Two available methods are used to predict the values of σh from σd and the calculated Id data are compared. Statistical tests performed for a total of six locations, including those used to develop the models, show that the best results are obtained when σh predicted with the method developed by Page is employed in the estimation correlation.