Simple correlation for estimating the global solar radiation on horizontal surfaces in India

A long range five years (2001–2005) measured data of the global solar radiation on horizontal surface along with the bright sunshine hours of four prominent cities viz. Jodhpur, Calcutta, Bombay, and Pune of India have been analyzed. The under considered cities have varying weather conditions of the country. The regression constants have been calculated for the first, second and the third order Angstrom type correlations for each location using regression analysis method. Comparisons of monthly mean global solar radiation (H¯) between the measured and the calculated values have been made. The statistical errors are also performed for testing the accuracy of regression constants. It is observed that in comparison to first order, second and the third order Angstrom type correlations do not improve the accuracy of the estimated global radiation. Therefore, using the measured data of all four cities together, we developed the first order Angstrom type correlations and presented new regression constants, applicable to all Indian locations. Furthermore, these regression constants of all India correlation are validated by comparison with the experimental and the other theoretical results available in literature.