Performance of empirical correlations for predicting monthly mean daily diffuse solar radiation values at Kampala, Uganda

Existing literature lacks information on formulation and performance assessment of diffuse solar radiation models in the Eastern African region yet this region has a high potential for the utilization of solar energy. The objective of this paper is to assess the performance of seventeen diffuse solar irradiation empirical correlations, at Kampala, Uganda. The best performing correlations were determined using the ranking method. The normalized absolute mean bias error and root mean square error were computed and utilized in the ranking process. The results indicated that the correlations relating diffuse transmittance ((H) over bar (d)/(H) over bar (0)) with relative sunshine duration ((S) over bar/(S) over bar (0)) are more reliable for diffuse solar radiation predictions at least in the Uganda environment. These models are expressed in terms of first, second and third order polynomials of the relative sunshine duration and are particularly recommended for their simplicity and worldwide applicability.