Generation of solar irradiance

on inclined surface using along terms measurements


K. Kabidi1*, M. N. Bargach2, R. Tadili2

1 Direction Régionale de la Météorologie du Nord, Direction de la Météorologie Nationale

2 Laboratoire d’Energie Solaire et d’Environnement, Faculté des Sciences de Rabat,

Université Med V – Agdal,  B.P 1014, Rabat, Maroc

* Corresponding author. Email:

Received: 21 December 2012; revised version accepted: 28 February 2013



     Since measurements of global and diffuse irradiances impinging on a sloped surface for most parts of Morocco are not available, the correlation relations and models used until now for estimating these values for the Moroccan stations were developed by Nfaoui and Ben Kaddour.

     In this paper, we develop the correlation existing between the clearness index Kt or the nebulosity Kd, and the monthly average daily sunshine fractions. Thirty years of sunshine duration measured data related to 28 Stations over Morocco, have been used to develop models estimating monthly mean values of radiation components. Models are obtained using the least square method, and given the highest correlation coefficients and the lowest standard errors, they are next tested and compared to the models Nfaoui and Ben Kaddour

     Using FORTRAN language, GRADS software and Geographical Information System (GIS), monthly maps of solar irradiation impinging on a tilted surface are plotted for the whole country. The values of monthly average radiation on titled surface range between 2.7 kWh.m-2 (in December) in Tangier (Lat: 34°43N, Long: 05°45W) and 7.7 kWh.m-2 (in June) in Ouarzazate (Lat: 30°56 N, Long: 06°54W).


Keywords: Sunshine duration; Global and diffuse irradiances; Titled surface; Clearness index.


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