The Disagreement between Anisotropic-Isotropic Diffuse Solar Radiation Models as a Function of Solar Declination: Computing the Optimum Tilt Angle of Solar Panels in the Area of Southern-Italy

Emanuele Calabrò

Department of Physics, University of Messina, Messina, Italy..

DOI: 10.4236/sgre.2012.34035                

Abstract

In this paper a simulation to maximize the global solar radiation on a sloped collecting surface was applied to typical latitudes in the area of southern Italy, to calculate the optimum tilt angle of solar panels on building structures or large photovoltaic power plants located in that geographical area. Indeed, the area of southern Italy and in particular Sicily and Calabria are the top of European locations for acquiring solar energy. Some models of diffuse solar irradiance were taken into account to determine panels inclinations that maximized the impinging solar radiation by means of global horizontal solar radiation data provided from the Italian Institute of ENEA (Italy). An algorithm was used for the simulation providing a set of tilt angles for each latitude. The optimum tilt angle values obtained from the simulation resulted to be strictly related to the model of diffuse solar radiation that was used. Indeed, the disagreement between the values obtained using anisotropic models of diffuse solar radiation and those obtained from the isotropic model resulted to decrease significantly with increasing solar declination, showing that the isotropic model can be reliable only in summer months.

Keywords

Global Solar Radiation; Diffuse Solar Irradiance; Isotropic Model; Optimum Tilt Angle; Solar Panel

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	B. Y. H. Liu and R. C. Jordan, “The Interrelationship and Characteristics Distribution of Direct, Diffuse and Total Solar Radiation,” Solar Energy, Vol. 4, No. 3, 1960, pp. 1-19. doi:10.1016/0038-092X(60)90062-1
[2]	A. Angstrom, “Solar and Terrestrial Radiation,” Quarterly Journal of the Royal Meteorological Society, Vol. 50, No. 210, 1924, pp. 121-126. doi:10.1002/qj.49705021008
[3]	S. A. Klein, “Calculation of Monthly Average Insolation on Tilted Surfaces,” Solar Energy, Vol. 19, No. 4, 1977, pp. 325-329. doi:10.1016/0038-092X(77)90001-9
[4]	L. Robledo and A. Soler, “Modeling Irradiance on Inclined Planes with an Anisotropic Model,” Energy, Vol. 23, No. 3, 1998, pp. 193-201. doi:10.1016/S0360-5442(97)00083-2
[5]	F. J. Olmo, J. Vida, I. Foyo, Y. Castro-Diez and L. Alados-Arboledas, “Prediction of Global Irradiance on Inclined Surfaces from Horizontal Global Irradiance,” Energy, Vol. 24, No. 8, 1999, pp. 689-704. doi:10.1016/S0360-5442(99)00025-0
[6]	L. Wenxian, G. Wenfeng, P. Shaoxuan and L. Enrong, “Ratios of Global Radiation on a Tilted to Horizontal Sur- face for Yunnan Province, China,” Energy, Vol. 20, No. 8, 1995, pp. 723-728. doi:10.1016/0360-5442(95)00016-A
[7]	J. LeQuere, “Rapport sur la Comparaison des Methods de Calcul des Besoins de Chauffage des Logements,” CSTB TEA-S 87, CSTB, Paris, 1980.
[8]	T. M. Klucher, “Evaluation of Models to Predict Insolation on Tilted Surfaces,” Solar Energy, Vol. 23, No. 2, 1978, pp. 111-114. doi:10.1016/0038-092X(79)90110-5
[9]	E. Calabrò, “An Algorithm to Estimate the Solar Energy Maximum Collection on Inclined Panels from Global Horizontal Solar Radiation,” International Journal of Sustainable Energy, 2012, Submitted.
[10]	S. Naihong, N. Kameda, Y. Kishida and H. Sonoda, “Experimental and Theoretical Study on the Optimal Tilt of Photovoltaic Panels,” Journal of Asian Architecture and Building Engineering, Vol. 5, No. 2, 2006, pp. 399-405. doi:10.3130/jaabe.5.399
[11]	E. Calabrò, “Determining Optimum Tilt Angles of Photo- voltaic Panels at Typical North-Tropical Latitudes,” Journal of Renewable and Sustainable Energy, Vol. 1, No. 3, 2009, Article ID: 033104. doi:10.1063/1.3148272