Multi-location approach to estimate solar energy radiation in the EU countries with a diffuse fraction correlation model

The availability of hourly and daily data of solar radiation represents an essential condition for the design and development of solar energy conversion systems. The most solar radiation data registered in common weather stations are global irradiance data on the horizontal plane. Nevertheless, the components of the global irradiance, i.e. direct and diffuse irradiance, are required for many purposes and they are often not immediately available requiring to be estimated. Aim of this paper is to present a parametric model to assess the components of solar radiation for European Union mainland analysing the solar radiation data available in the World Radiation Data Centre (WRDC) collected from 44 weather stations of 11 European countries. A correlation analysis among the solar radiation components has been conducted considering different regression functions and the best fitting one was determined by means of different statistical indices as key performance factors. The developed model allows predicting the diffuse and direct irradiance profiles for a generic European site, considering its climate conditions. Finally, this paper presents an application of the proposed approach, in particular the multi-location model has been applied to determine the solar radiation components on a tilted surface in the city of Bologna (Italy).