Accurate computations of monthly average daily extraterrestrial irradiation and the maximum possible sunshine duration

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Abstract The monthly average daily values of the extraterrestrial irradiation on a horizontal plane ( H 0 ) and the maximum possible sunshine duration ( S 0 ) are two important parameters that are frequently needed in various solar energy applications. These are generally calculated by solar scientists and engineers each time they are needed and often by using the approximate short-cut methods. Using the accurate analytical expressions developed by J.W. Spencer [Fourier series representation of the position of the sun, Search 2, 172 (1971)] for the declination and the eccentricity correction factor, computations for these parameters have been made for all the latitude values from 90°N to 90°S at intervals of 1° and are presented in a convenient tabular form. Monthly average daily values of the maximum possible sunshine duration as recorded on a Campbell-Stokes sunshine recorded S ′ 0 are also computed and presented. These tables would avoid the need for repetitive and approximate calculations and serve as a useful ready reference for providing the accurate values of H 0 , S 0 and S ′ 0 to the energy scientists and engineers.