Since 2012, the Italian solar park has greatly expanded and changed, as new systems based on Si-type IBC and HJT cells, tandem cells, bifacial modules, and single- and dual-axis tracking systems are becoming increasingly popular. Estimating solar output by these new technologies requires not only the knowledge of the global but also accurate information on the direct and diffuse components of solar irradiance, since photovoltaic output depends on the actual amount of solar energy exploited by the different kinds of cells and installations.

For some types of modules, it is also necessary to know the spectral shape of the irradiance because different layers can exploit different portions of the solar spectrum. Detailed information on irradiance provides a necessary basis for planning the siting of new photovoltaic system technologies and their performance evaluation and operation management. The Automatic Radiative TransfEr Model for Irradiance with Satellite data (ARTEMIS) system aims to provide the most accurate possible estimation of spectra and integrated values over the solar band of the direct normal and diffuse component of solar irradiance at a spatial resolution of about 4 km and temporal resolution of 15′ over the entire national territory.

During this year, the methodology, whose development began in previous years and allowed estimation under clear sky conditions, was refined to obtain spectral irradiance estimation even in the presence of cloudiness in near-real time. The method exploits satellite and numerical meteorological data provided by various sources. For estimation under cloudy conditions, a specialized library was used, which requires more data than under clear sky conditions, such as spectral albedo and data characterizing atmospheric aerosols, as well as describing the vertical structure of the atmosphere and clouds detected by the Meteosat Second Generation (MSG) geostationary satellite.

To this end, statistics on the spatial and optical characteristics of clouds were obtained, and then exploited in the algorithm, by cross-referencing data from MSG and a recently installed celiometer in Milan owned by RSE. Care was also devoted to computer optimization of the code so that the calculation time of spectral radiation over all of Italy would not exceed 6 minutes.

This year the SunRiSE WebGIS portal was also updated with maps of daily normal, diffuse and global direct irradiance under clear sky conditions and maps of PV production forecasts for the seven Italian market areas.

The Report is available on the Italian site