With the perspective of Switzerland’s phase-out from nuclear energy, solar energy potential may take an important role for the country’s future in renewable energy. Based on 12 years of satellite-derived, spatially distributed data of daily average cloud factor, this work analyses cloud cover persistence over all of Switzerland. We used extreme value analysis to study spatial variation of extremal behaviour and to estimate return levels of weeklong cloud cover events throughout Switzerland. Extreme events show different patterns in winter and summer, but overall they occur more frequently and more severely in the northern part of the country and in Ticino.