Evaluation of Empirical Models for Estimating Daily Solar Radiation Temperature-Based in Four Climate Region of Iran

Daily solar radiation is an important element in the application of solar energy. Measuring solar radiation requires advanced tools and equipment. Hence, solar radiation measured data are not always available in the all the meteorological stations. Generally it needs to be estimated by empirical models based on frequently available meteorological records such as hours of sunshine or temperature. This paper evaluates the behavior of five empirical models based on the difference between maximum and minimum temperatures (the models of Bristow & Campbell, Hargreaves, Samani, Chen and Li). With statistical error tests, the performance of the models is validated by comparing together against the measured data at 12 meteorological stations in Iran located in four region climate humid, semi-humid, semi-arid and arid. Results show that the models are more accurate in the arid regions as compared to humid regions. Hence, these models can be recommended for estimating daily solar radiation in arid regions where only air temperature data are available in Iran.