EFFECT OF RAINFALL ON THE ESTIMATION OF MONTHLY MEAN HOURLY SOLAR-RADIATION FOR INDIA

The constants in the empirical equations to predict hourly solar radia tion on a horizontal surface recommended by ASHRAE were modified by th e authors [1] for Indian locations. In further studies, India is divid ed into four regions of rainfall, namely, region of heavy, medium, low and very low rainfall. Using ASHRAE equations with the modified const ants, monthly-mean-hourly solar radiation values are estimated for ten cities from different regions of India. From the comparative data ana lysis of the measured and estimated solar radiation of these cities, e mpirical correction factors for the four regions of rainfall were obta ined. The statistical analysis is carried out for the computed data wi th and without considering correction factor for rainfall and the meas ured data for four randomly selected Indian cities. Two statistical in dicators, namely, mean percentage error and normalized root mean squar e error, are used to compare the accuracy of the developed procedure. The results show that the yearly average normalized root mean square e rror with Indian constants, considering effect of rainfall for these f our Indian cities, is found to reduce to 14.86, 12.15 and 7.61% for mo nthly-mean-hourly beam, diffuse and global radiation respectively on h orizontal surface, as against the corresponding values of 23.29, 22.2 and 16% without considering the correction for rainfall. (C) 1998 Else vier Science Ltd. All rights reserved.