ESTIMATION OF SOLAR RADIATION ENERGY OF ETHIOPIA FROM SUNSHINE DATA

Measurements of global solar radiation on a horizontal surface, for nine meteorological stations in Ethiopia, are compared with their corresponding values computed based on Ångström relations, Regression coefficients are obtained and correlation equations are determined to predict the global solar radiation. The result shows that Ångström relations are valid for Ethiopian locations, and the correlation equations can be used to predict the monthly mean daily global solar radiation in the locations considered in this study.

This study also proves that the results made by ENEC et al, using the generalised Frere's coefficients, is unsatisfactory for the prediction of monthly mean daily global solar radiation. On the other hand, the work of Dogniaux and Lemoine, using the regression coefficients a and b as a function of latitude and atmospheric turbidity and grouping large range latitudes to extend the application, can give better estimation. However, for more accurate estimation, several additional meteorological stations have to be evaluated and their regression coefficients have to be determined before grouping in to one relationship to express the variations of a and b under any conditions of equipment and location.