Dumas Relationships Applied to Two Italian Sites. A Comparison among Various Solar Energy Estimating Formulas

In this paper different methods for a predictive estimation of solar radiation are compard. The timeframe is 2007-2009. The comparison has been made on two sites, Manfredonia and Portici, both located in the south of Italy. Even if these sites are relatively near and subjected to a temperate climate, typical of Mediterranean region, they present some important differences in local micro- climate, which affects atmospheric behavior, particularly in the daily temperature variations. The method for estimating solar radiation proposed by Dumas (1984) has been tested and compared with various solar radiation empirical formulas, correlating solar radiation energy with temperature, as the well known Bristow-Campbell and Hardgreaves-Samani models. This preliminary study shows the potential of the Dumas method, even in the tested locations. It also shows that the Dumas relation actually performs better then the models mentioned above, in particular for sites with low values of daily temperature variations. In some cases it even offers a comparable accuracy with respect to the Ångström-Prescott formula.