In a revolutionary move for renewable energy, Switzerland has officially inaugurated the world’s largest foldable solar roof at the ARA Thunersee wastewater treatment plant in Uetendorf. Spanning an area equivalent to three football pitches, the project marks a new global benchmark for “dual-use” infrastructure.
The innovative system, developed by the Swiss firm dhp Technology, was commissioned in September 2025 and officially celebrated this month. By building vertically over existing wastewater basins, the city of Uetendorf has managed to generate massive amounts of clean energy without occupying a single square meter of new land—a critical factor in land-scarce regions.
Unlike traditional stationary solar farms, the Uetendorf installation features the patented HORIZON system. Inspired by Swiss cable-car engineering, the lightweight solar modules are suspended on high-tension cables and equipped with a fully automated folding mechanism.
In the event of strong winds, heavy snow, or hail, the entire roof automatically retracts into a protected storage position within minutes.
Because the modules are suspended up to 7 meters high with 20-meter spans between supports, plant operators maintain full, unobstructed access to the treatment basins below for maintenance and inspection.
The scale of the “Infinity Roof” at ARA Thunersee is staggering: | Statistic | Detail | | :— | :— | | Total Surface Area | 20,000+ m² (over 23,000 m² of module surface) | | Installed Capacity | 3.6 MWp | | Annual Energy Yield | ~3,000 – 3,400 MWh | | Homes Powered | Equivalent to ~700 households | | Material Efficiency | 50% less material than rigid structures |
Wastewater treatment is energy-intensive, often accounting for more than 1% of a country’s total electricity consumption. The Uetendorf project already provides one-third of the plant’s total energy needs, shielding the utility from volatile energy market prices.
“We are using existing space intelligently,” said Ingo Schoppe, Managing Director of ARA Thunersee. “The folding solar roof delivers operational safety while making a meaningful contribution to climate protection.” With the success of this flagship project, officials expect the foldable solar model to be exported globally, with potential applications for parking lots, logistics hubs, and highway rest areas.
