DIFFUSE SOLAR-RADIATION OVER SHAMBAT, KHARTOUM NORTH

There are many locations where no measured data on diffuse radiation are available and have to be estimated from empirical correlations. Here, using correlations for predicting monthly mean daily diffuse radiation on a horizontal surface for locations in Sudan, from the experimental data of Shambat station, the applicability of the developed equations were tested by estimating monthly mean daily diffuse radiation for the location. Measurements of diffuse radiation on a horizontal surface at Shambat for 10 years were compared with predictions made by several independent methods. In the first type of correlation, formulae were used to correlate diffuse solar irradiance to the clearness index. Regression coefficients are obtained and used for prediction of diffuse solar irradiance. The predicted values were consistent with measured values (10.13%). In the second type of correlation, sunshine duration and minimum air mass were used to derive an empirical correlation for diffuse radiation. The predicted values compared well with measured values (16.31%). In the third type of correlation, a correlation connecting monthly mean daily diffuse radiation together with the clearness index and per cent possible sunshine is found to be 9.66%, the most accurate for the Shambat location.