Switzerland has switched on what is now considered the world’s largest foldable rooftop solar installation, a 3.6 MW system built above the Thunersee wastewater treatment plant in the canton of Bern. The project, described by pv magazine, uses a retractable photovoltaic roof spanning more than 23,000 square meters.
The array, developed by dhp Technology, stretches across several open treatment basins, turning unused overhead space into a power-generating platform. This dual-use model lets the facility continue normal wastewater operations at ground level while producing about 3 GWh of solar electricity each year, most of which will be consumed on-site.
The folding structure is based on Swiss cable car engineering. During heavy snow, hail, or storms, the system can fully retract itself to avoid damage and then redeploy once conditions stabilize. The design helps maintain long-term reliability without the need for extensive protective infrastructure.
The Thunersee plant’s management says the project demonstrates how existing industrial sites can help accelerate the energy transition without requiring new land. By installing solar modules above treatment basins, the facility boosts its energy independence while reducing exposure to electricity price fluctuations.
dhp Technology says the concept is scalable and well suited for locations where rooftop space is irregular or where traditional ground-mount solar farms are not viable. The company has previously installed smaller versions of the folding-roof system, but the Thunersee project is the largest deployment so far.
Plant director Ingo Schoppe said the installation shows how utilities can adopt practical solutions that support supply security and climate goals while keeping operations efficient. The long-term plan is for the solar output to cover a major share of the facility’s annual power demand, turning a critical piece of wastewater infrastructure into a cleaner and more self-sufficient energy consumer.