A method for estimating monthly global solar radiation

In this paper a method is followed for estimating monthly totals of global solar radiation from a combination of calculations of monthly cloudless global solar radiation, surface meteorological observations, and empirical formulae relating sunshine duration to global solar radiation. The percent deviation of calculated from observed values is not negligible, but is much less than errors obtained by using extraterrestrial solar radiation totals. In case of values of monthly global solar radiation which are estimated for other regions, the resulted possible errors should be determined again. Some techniques leading to adaptation of the regression equations for other areas are argued.