Swiss rooftops are producing more and more solar power

This figure is considerably higher than that suggested by a comparable study covering the period between 2017 and 2021, which indicated a utilisation rate of just 50 percent. “Our investigation reveals a clear trend reversal: those incorporating solar installations on their rooftops are now utilising the available space much more consistently than was the case just a few years ago,” says Professor Jürg Rohrer, Head of the Renewable Energies Research Group at the ZHAW. “This is good news – we could, in purely theoretical terms, already almost achieve the national expansion targets for renewable energies using existing rooftops.”

However, the degree to which this potential is realised varies greatly between the different building size categories: in small buildings (typically single-family homes with potential rated output of less than 30 kWp), it was found that 93 percent of the available potential was utilised on average. For medium-sized buildings (e.g. larger residential buildings and commercial properties, 30 to 150 kWp), this figure stood at 76 percent. Due to complex ownership structures, such as condominium ownership arrangements, the utilisation and billing of collectively generated solar power in these buildings is significantly more challenging, which is slowing down expansion.  On large rooftops (industrial, logistics and large public buildings with a potential rated output of in excess of 150 kWp), a utilisation rate of 58 percent means significant reserves remain untapped.

If new PV systems continue to make similarly consistent use of rooftops as they did in 2023 and 2024, the expansion targets for renewable energy anchored in the Federal Electricity Supply Act could, in purely theoretical terms, be achieved using rooftop photovoltaics alone. However, for this to become a reality, the rate of expansion would have to increase considerably.