Evaluation of the global solar irradiance in the Vhembe district of LimpopoProvince, South Africa, using different theoretical models

Abstract

An attempt has been made to employ three different theoretical models for the determination of global solarradiation for the climate conditions of the Vhembe district of Limpopo Province in South Africa. The models are: 1)the Angstrom linear-based model, 2) the Hargreaves and Samani (temperature-based) model, and 3) the Garcia model.These models require the following meteorological data inputs: temperature, sunshine hours, and global solar irradianceon the horizontal surface. The regression coefficients from our previous study were also employed in the calculations.A 4-year (2007{2010) global solar irradiance and temperature data set from the Agricultural Research Council and theactual sunshine data set from the South African Weather Services were used. The monthly average global solar irradiancefor the four selected areas of study were computed and compared with the in situ data. The results obtained show thatthe Angstrom linear and temperature-based models are suitable methods for predicting the global solar irradiance inthis study area. The difference between the observed and the predicted data is less than 6.5 MJ/(m2day). Their rootmean square error varies between 0.0112 and 0.0368. Graphical representations of the irradiances versus the days of theyear showed high values during summer for all the models used.