SOLAR RADIATION STUDIES AT KARACHI PAKISTAN

Solar radiation studies have been carried out to work out the feasibility of possible and efficient utilization of Solar Energy at Karachi, Pakistan.From the analysis of the monthly average daily and hourly global solar radiation data, the prospects of solar energy utilization are very bright.Karachi receives about 19.50 MJm-2d-l of solar isolation with an annual total of 7000 MJm-2 .The influx of global solar radiation is very consistent and has a variation of only 22.8% in the last 27 years. Except for the monsoon months, solar radiation incidence is very encouraging, from the application point of view. Correlation equation of the first and second order polynomials have been developed for Karachi, to estimate the monthly average daily diffuse solar radiation, employing relative sunshine hours and clearness index. The diffuse radiation shows a peak value during monsoon months, while average diffuse to global ratio is 0.32 and diffuse to extraterrestrial ratio is 0.19, throughout the year.The results from these correlations are in agreement with the results from Page's equation.Stanhill and Iqbal overestimates, while Liu and Jordan underestimate the diffuse radiation value.Monhly average hourly diffuse radiation have also been studied and analysed. Monthly average of hourly and daily global solar radiation incident on an inclined, south facing surface has been computed from solar radiation data. The Hourly and daily values of solar insulation on inclined surfaces are then compared. The difference between the results obtained is very small. Annual and monthly average of solar radiation are also evaluated from hourly values besides averages for the heating and cooling seasons .Monthly and annual variations of global solar radiation incident on inclined surface for various off south orientation and inclinations have also been computed. From the results, west of south orientation is not recommended at all, for Karachi, as far as solar energy income is concerned.Estimation of monthly average daily global solar radiation on horizontal surface via six different correlations and its comparison with the measured data recommends Angstrom's equation and Frere et al.relation to be the best for use. The regression constants 'a' and 'b' show year to year fluctuations with an average value of a=0.326 and b=0.405,in agreement with the predictions of Modi and Sukhatme.The sum (a+b) however remain fairly constant, through the years. These prediction formulae are then subjected to statistical tests in order to establish the superiority of one correlation over the other. Correlation equations have also been developed for Karachi, to obtain the monthly average daily global, beam and diffuse solar radiation from the fraction of possible bright sunshine hours. The global, beam and diffuse radiation obtained via these correlations are then compared with the measured data with fine agreement. Diffuse and beam radiation can also be estimated even in the absence of global solar radiation