6533b7d7fe1ef96bd1267969

RESEARCH PRODUCT

A simple model for computing diffuse solar radiation

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In this paper a very simple model for predicting the daily diffuse solar radiation at any Italian location using as input few extensively measured meteorological parameters is proposed. In fact the daily diffuse radiation D, MJ.m−2.day−1, here is correlated with only the relative sunshine duration sS and the noon altitude of the sun on the 15th of the month hn, degrees, by the following equation: D=7(sS−(sinhn)1.55 . The validity of this formula is verified using monthly mean daily data from four Italian stations displaced at various latitudes or altitudes or geographical situations (inland or coastal site). The test results show that the deviations between the measured and the computed values of D are generally low; the maximum standard per cent error of estimate Φ (%) is less than 10. Moreover a comparison of the values of D computed for each tested station by the present formula and the others considered correlations with experimental data is showed. This comparison points out that the standard per cent error of estimate Φ (%) referring to the present equation is better than ones obtained for the other considerd correlations for Adrano, Palermo and Genova whereas it is almost equal for Macerata. Consequently the very simple model herein proposed results independent of the latitude, the altitude and the geographical situation of the place and reasonably it can be considered valid and useful to predict the daily diffuse solar radiation at all Italian locations lacking in data records of diffuse radiation with good reliability.