Solar radiation measurements in the Alps: a comparison of different datasets

Accurate measurements of the solar radiation available at the Earth's surface are essential for a wide range of practical applications in the field of renewable energy and agriculture, as well as for the investigation of climatological and hydrological processes. In particular, the characterization of the temporal and spatial distribution of incoming solar radiation is very challenging in mountainous areas, where orographic shadowing and altitude effects, together with local weather phenomena, greatly increase its variability. At present, many different methods are employed for solar radiation mapping, including the interpolation of surface measurements and the orographic downscaling of satellite data. The accuracy and the suitability of these two approaches for complex-topography regions are still under debate.

A high-resolution (200 m) solar atlas has been recently developed for the Alpine region of Trentino in the Southern Alps, on the basis of global radiation observations provided by the local radiometric network for the years 2004-2012. Monthly and yearly climatological radiation maps were obtained by combining a GIS-based clear-sky model (r.sun module in GRASS GIS) with geostatistical interpolation techniques (kriging). Moreover, 2-km resolution satellite data derived by the MeteoSwiss HelioMont algorithm were used for missing-data reconstruction and in the final mapping, integrating ground-based and remote-sensing information. The results are compared with existing solar radiation datasets for the region of interest, such as the two PVGIS databases produced by the Joint Research Center Institute for Energy and Transport. The accuracy of the different ground- and satellite-based datasets is evaluated for the study area, also in comparison with long-term simulations carried out by means of the WRF model for the study area (2-km resolution).