Fuzzy Modelling of Hourly Global Solar Irradiation from Sunshine Fraction and Cloud Cover

This paper presents two new models for calculating hourly global solar irradiation (HGSI) suitable for use where there are no relevant measurements. The models are based on a fuzzy algorithm using hourly sunshine (first model) and cloud data (second model). Solar irradiation measurements are not easy to obtain because of the expensive measuring equipment and techniques required. The model has been developed and tested for major cities of South Korea, during the period (1981-2010). Results of cloud cover and sunshine fraction models have been compared with the measured data using the coefficient of determination (R2), root-mean-square error (RMSE) and mean bias error (MBE). This showed that the fuzzy models were considerably more accurate and could be used for many regions as compared to sunshine fraction and cloud cover modes. It may be concluded that the fuzzy models of sunshine fraction and cloud cover presented in this study may be used reasonably well by building designers in estimating the hourly global solar irradiation where only the cloud and sunshine observations are available