Generalized models for estimation of global solar radiation based on sunshine duration and detailed comparison with the existing: A case study for India

The main objectives of this work are the comparison and the development of models for estimating mean monthly global solar radiation in India. Meteorological data for a 15-year period (1986-2000) are used for 23 locations across India from Indian Meteorological Department, Pune. Quality control of data is performed and appropriate limits were established. From the literature, 104 models were nominated which correlate clearness index to relative sunshine duration. Models were subsequently applied to the used data. Furthermore, 7 new 'generalized' models are developed using all data. Comparison and performance assessment of all the models is conducted using some well-known statistical indicators. Moreover, statistical indicators were scaled to obtain Global Performance Indicator which is subsequently used to rank the models. According to the results, the Global Performance Indicator takes values between -7.2627 and 0.9065. The developed generalized models present superior performance compared to those nominated from literature. Top ranking models are used to assess solar radiation for six stations under different climates and it is established that these models have strong estimation capabilities. So, this study determines the most precise model demonstrating generalized behavior to assess global solar radiation anywhere in the region.