In the last decade, the energy transition began with an ever-increasing penetration of renewable sources in the energy production sector. Among renewable sources, solar is expected to grow further in the coming decades at a global level and in Italy, also in order to achieve the objectives of containing the effects of climate change. In this context, concentrating photovoltaics (CPV) could make a significant contribution thanks to its high efficiency. In order to identify the most suitable locations for the installation of new CPV plants, based on the availability of the primary resource and to deepen the knowledge of the relationships between the different types of CPV cells and the distribution of spectral direct normal irradiance (SDNI) on captation surface, it would be appropriate to have reliable SDNI measurements throughout the Italian territory. These measurements are rarely made, due to the high costs of the necessary tools and their need for continuous maintenance. Methods for indirect estimation of SDNI are therefore being developed, based on meteorological information closely related to SDNI.

Accurate ground measurements are also required to validate these new methodologies. To meet the demand for spectral irradiance data, in 2019 RSE also managed and enhanced the first national SDNI measurement networks, with measurements made by members of the HELIOS consortium.

To increase SDNI measurements in areas of Italy with a high potential for CPV development, RSE installed a spectrophotometer in the Cagliari area, thanks to a collaboration with Sardegna Ricerche and Università di Cagliari, in a site equipped with experimental CPV modules. This made it possible to perform the first comparative analyses between power data and SDNI measurements. The comparisons highlighted the important effect of atmospheric components, such as precipitable water content, ozone, presence of aerosols on the spectral distributions of DNI and the consequent production.

This type of study provides significant indications for the research of new systems for estimating or forecasting SDNI and, in parallel, for developing CPV production estimation methods, suggesting which are the determining parameters for production. Consequently, it is necessary to estimate and predict these parameters with the greatest possible accuracy to achieve a good CPV production forecast.

The RADSAF database containing estimates of global irradiance on a horizontal plane has also been populated with satellite data, relating to the whole of Italy, with a spatial resolution of 4.5 km and a temporal resolution of 15 minutes, starting from 2005 to today.

RADSAF data has been made available this year for the IEA’s international Photovoltaic Power Systems Programme (PVPS) to support PV penetration in the electricity system. Collaboration with IEA PVPS Task 16 Partners has enabled comparison of different PV generation forecasting models for aggregate areas by market zone and the entire country.

Finally, always for the purpose of validating various methodologies for estimating and forecasting solar irradiance components, data acquisition and management of the solar station were also maintained at the RSE headquarters in Milan.