Local radiation maxima in snow-covered mountains and its influence on PV winter production

Mountains receive increased solar radiation because of a thinner atmosphere, the presence of snow on the ground and – in many regions such as the Alps – decreased winter cloudiness. In complex terrain, multiple terrain scattering further leads to radiation concentration at certain locations. We quantify this effect and present for the first time a surface radiative transfer model, which combines a bidirectional reflectance distribution function (BRDF) with multiple terrain scattering. It is shown that both effects, the anisotropic scattering properties of snow and the multiple terrain scattering contribute significantly to local radiation maxima and lead to an average increase in area-wide radiation input. This has not only implications for the local surface energy balance but also for PV production in snow covered mountains: high elevation installations of PV panels at steep angles can produce a large amount of winter electricity in mid latitudes. Using the example of Switzerland, it is shown how this can help to close an existing winter energy gap.