Global solar radiation models: A critical review from the point of view of homogeneity and case study.

Access to reliable solar radiation data is of paramount importance for the sustainable development of mankind. However, solar radiation measurements are available in few meteorological stations, so models are used to estimate global solar radiation from other climate variables. This paper presents a compilation of 165 global solar radiation models that is representative of the progress over the last 100 years. The models were classified according to the type of variables used and a large majority of dimensionally non-homogeneous equations were identified. Furthermore, it was observed that comparisons between various models studied in different regions over recent decades were occasionally contradictory, so that no single existing model seems to have definitively outperformed the others. In this context, homogeneity analysis provides a procedure to improve the quality of models by reducing the presence of variables implicit in numerical coefficients, which deserves to be valued as a methodological tool. In addition, a previously introduced temperature-based homogeneous model was updated using recent experimental data and revising the functional form of the local geographic factor dependent on elevation and distance to the sea. Using site-calibrated coefficients, the modified model provides accurate results at 22 meteorological stations in northern Spain, located over a distance of about 1000 km. Using a general equation, acceptable predictions are obtained for the 21 stations with the highest climatic similarity. • Homogeneity analyses are performed on 165 radiation models for the first time. • Implicit variables in coefficients limit model validity for diverse climate zones. • Any solar radiation model based on a non-homogeneous equation can be improved. • A homogeneous temperature-based model is valid at Spanish stations 1000 km apart. [ABSTRACT FROM AUTHOR]