Solar radiation estimates from sunshine hours on horizontal surface at Karachi, Pakistan

A regression analysis of the relative monthly values of global solar radiation corresponding values of sunshine for the period of seven years was carried out to determine the constants a and b of the Angstrom formula, for Karachi. These constants were also obtained by method of Rietveld and the graphical method of Frere et al. The values of regression constants evaluated for Karachi are in close agreement with the predicted values of Modi and Sukhatme for Pakistan. Solar radiation for Karachi was estimated from these methods and compared with the measured values. A good correlation is found between measured and estimated radiation. (author)