The World’s Largest Folding Solar Roof – Rethinking Energy Production on Infrastructure Sites
A New Chapter for Renewable Energy in the Water Sector
At the Thunersee wastewater treatment plant (ARA Thunersee) in Uetendorf, a project has been realised that is redefining energy production in the water sector: the largest folding solar roof in the world. With the HORIZON photovoltaic system from dhp Technology, the space above several treatment basins is used to generate renewable energy exactly where it is needed — without additional land consumption and without interfering with ongoing operations.
Output, Dimensions and Energy Yield
The system was commissioned in September 2025 and officially inaugurated on 31 October. With an installed capacity of 3.6 MWp and a module surface of over 23,000 m², the solar roof generates around 3 GWh of solar power per year, corresponding to the annual consumption of about 700 households. ARA Thunersee now covers a significant part of its electricity demand itself, strengthening security of supply, economic resilience and climate protection.
Automatic Weather Protection for Maximum Operational Safety
A core feature of the solar roof is the fully automated folding mechanism, based on proven Swiss ropeway technology. In favourable weather, the photovoltaic modules are extended to maximise energy production. During storms, snow or hail, the roof retracts automatically into a protected position. This intelligent mechanism combines high energy yield with maximum safety — crucial for critical infrastructure.
Energy Production Without Disrupting Operations
The solar roof has been designed to integrate seamlessly into day-to-day operations. All treatment and process stages of the plant remain fully accessible and can continue without any restrictions. For maintenance, service or inspection work, the system can be partially or fully folded, ensuring complete access to the basins from above whenever required. The system supports the daily operation of the plant rather than obstructing it — a decisive advantage over static roof structures.
“We wanted a solution that uses our infrastructure twice while guaranteeing the highest level of operational safety. The folding solar roof delivers exactly that.”
– Ingo Schoppe, Managing Director, ARA Thunersee
Economic Benefits Through On-Site Power Generation
Wastewater treatment plants are among the most energy-intensive municipal infrastructures. Pumps, blowers, mixers, dewatering and control systems run around the clock. Generating a substantial share of electricity directly at the site results in stable and predictable energy costs, lower dependence on external power markets and a significantly improved economic resilience of the plant.
“Energy costs are a major factor for us. With the folding solar roof, we can cover a considerable share of our demand ourselves — this is a major step forward for our cost efficiency.”
– Ingo Schoppe, Managing Director, ARA Thunersee
From Concept to Commissioning
The realisation of the solar roof proceeded in several stages — from feasibility study and approvals to engineering and installation during ongoing operations. Commissioning is not the end of the journey, but the beginning of a reference project with relevance far beyond the water sector.
A Scalable Model for Europe
The project demonstrates how existing infrastructure surfaces can actively contribute to the energy transition. The concept can be applied not only to wastewater treatment plants but also to logistics areas, parking and traffic zones, industrial sites and other infrastructure facilities. Energy is generated where it is consumed — without requiring additional land.
“With HORIZON, we demonstrate how infrastructure surfaces can contribute to the energy transition — without compromising functionality or aesthetics.”
– Gian Andri Diem, dhp Technology
Conclusion
ARA Thunersee shows that infrastructure sites can become valuable energy resources for the future.
The world’s largest folding solar roof combines technological innovation, environmental responsibility and economic benefit — and proves that climate action on existing infrastructure is possible today. It serves as a benchmark for Switzerland and Europe and sets a new standard for sustainable energy production in the infrastructure sector.
