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RESEARCH PRODUCT

Diffuse solar radiation statistics for Italy

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Abstract In this paper diffuse radiation is correlated with usually measured or more easy computable quantities in order to have a larger number of data available for the various applications of solar energy. Here are used two types of correlation: (a) diffuse radiation as a function of global and extraterrestrial radiation; (b) diffuse radiation as a function of ralative sunshine and extraterrestrial radiation. On the basis of the above correlations, empirical equations have been proposed and their coefficients have been calculated by fitting the experimental data of three Italian stations. The degree of accuracy of the fit has been estimated by a coefficient introduced and called by us “relative standard error of estimate.” In order to compare the proposed formulas, which have different degrees of freedom, it has been used the test of Gauss modified by us. The values of diffuse radiation obtained by the proposed relations agree very well with the experimental data.