Achieving the European Climate Neutrality Goal by 2050 requires further enhancement of energy production from renewable sources. According to Italy’s National Integrated Energy and Climate Plan, significant growth is anticipated in solar photovoltaic (PV) installations, with a target of 50 GW by 2030 compared to the current 21 GW. This development must be accompanied by careful planning, which involves identifying the most efficient technologies based on the available primary resource. Therefore, it is crucial to accurately characterize the entire territory in relation to solar radiation. It is important to assess both the global horizontal irradiance (GHI), closely linked to flat-plate PV production, and the direct normal irradiance (DNI), due to its impact on high-efficiency PV production achieved with solar tracking systems and concentrating photovoltaic (CPV) systems. To this end, by the end of the three-year period, RSE aims to produce direct normal solar radiation maps for the national territory, obtained using an innovative method under development in the RdS 2.2 project. This method will estimate DNI based on environmental factors that determine its intensity. For the development and validation of the algorithm, spectral radiation measurements are required to deduce the environmental factors affecting DNI. During the year, RSE has managed and enhanced the national network of spectral direct normal radiation measurements (SDNI) through the HELIOS consortium, involving several Italian institutions, structuring the data into a suitable database and analyzing the collected measurements.

In relation to GHI, the RADSAF database of satellite estimates of horizontal irradiance across the entire Italian territory has continued to be updated, with a spatial resolution of 4 km and a temporal resolution of 15 minutes. These estimates have been made publicly available daily on the web GIS portal http://sunrise.rse-web.it/, and have also been used to support other RdS projects.

Since accurate ground radiation measurements are obtained only with expensive and maintenance-intensive instruments, they are quite rare in Italy. This situation has often led to indirect estimation methods, such as those based on satellite data, not being tested on our territory. Thanks to the maintenance and enhancement of the solar measurement station in Milan throughout the year, RSE’s data have been made available to the International Energy Agency – Photovoltaic Power Systems Programme (IEA-PVPS) for benchmarking different methods of estimating and forecasting GHI and DNI. The data were subjected to stringent validation according to best practices defined within Task16 of the IEA-PVPS, with RSE’s contribution. These best practices are described in this report.