Zizers, 31 October 2025 – The world’s largest foldable solar roof has been officially inaugurated at the ARA Thunersee wastewater treatment plant. Swiss Federal Councillor Albert Rösti personally attended the ceremonial opening during a site visit. The installation will produce around 3 million kilowatt-hours of solar electricity per year and represents a significant milestone for Switzerland’s renewable energy supply. The project was developed and realised by the Swiss cleantech company dhp Technology AG, based in Zizers (GR).
The innovative foldable solar roof spans several treatment basins and makes dual use of existing infrastructure surfaces – wastewater treatment below and solar power generation above. Based on proven Swiss cableway technology, the roof can automatically fold up in extreme weather conditions such as storms, snow or hail. This combines operational safety with reliable energy production – without interfering with the plant’s ongoing processes.
“This project demonstrates how we can advance the energy transition in a pragmatic and effective way,” said Ingo Schoppe, Managing Director of ARA Thunersee, at the inauguration. “By making intelligent use of existing surfaces, we actively contribute to security of supply, economic efficiency and climate protection. The foldable solar roof strengthens our energy independence and serves as a model for other infrastructure facilities.”
With an installed capacity of 3.6 megawatts peak, the system generates around 3 gigawatt-hours of renewable electricity annually – equivalent to the consumption of approximately 700 households. A large share of the electricity produced is used directly on site, marking an important step towards self-sufficiency and sustainable plant operation.
“ARA Thunersee proves that infrastructure is part of the energy future,” said Gian Andri Diem, CEO of dhp Technology. “The world’s largest foldable solar roof stands in Switzerland – developed with Swiss engineering expertise and innovative spirit. This project highlights the enormous potential of energy generation on existing surfaces, creating progress without consuming additional land.”
Project data
Location: ARA Thunersee, Canton of Bern
Technology: HORIZON foldable solar roof by dhp Technology
Module area: over 23,000 m²
Capacity: 3.6 MWp
Annual production: approx. 3 GWh
Special feature: foldable PV system with automatic weather protection
Benefits: dual land use, high on-site self-consumption rate
Wastewater treatment plants, logistics areas, water utilities and parking facilities offer significant potential for energy generation. The HORIZON foldable solar roof enables sustainable electricity production on surfaces that were previously unused – without soil sealing, without land-use conflicts and with maximum operational safety.