When conducting a feasibility study for the installation of photovoltaic panels, it is crucial to know the direct and diffuse components of solar radiation that reach the ground. Numerous decomposition methods have been developed to estimate the diffuse part using different predictors because, in most cases, only the global component is available. However, these models have rarely been evaluated in mountainous environments. For this reason, the first objective of this study is to assess the performance of decomposition models in alpine contexts. Six models—Orgill & Hollands, Erbs, DISC, DIRINT, Reindl, and Boland—are assessed by comparing the estimated diffuse and beam irradiance with real measurements using datasets gathered from 19 Swiss meteorological stations at different elevations.