Germany’s future largest solar folding roof is currently being built at the Stuttgart-Mühlhausen main wastewater treatment plant. Above the aeration tanks of the northern biological treatment stage, Stadtentwässerung Stuttgart (SES) and dhp Technology are implementing a photovoltaic system with an installed capacity of around 2.75 MWp.
The HELIOFLEX® solar folding roof comprises 120 folding roof groups and spans an area of approximately 18,000 square metres. Construction began on 8 July 2026, with commissioning scheduled for January 2027.
Solar power for a major energy consumer
Around 190,000 cubic metres of wastewater are treated every day at the Stuttgart-Mühlhausen main wastewater treatment plant, together with the residues generated during the process. This results in a substantial and continuous demand for energy.
The solar power generated above the aeration tanks can be used directly for the biological wastewater treatment process or distributed to other consumers within the treatment plant via the existing medium-voltage network.
Solar energy is therefore generated exactly where it is needed: directly on the site of a major municipal energy consumer.
A solar folding roof on a new scale
From a technical perspective, the project also reaches an exceptional scale. The system is being implemented in two construction phases and comprises a total of 60 suspension cables, along which the 120 folding roof groups move.
The project also requires extensive electrical infrastructure. The planning includes 20 inverter positions as well as DC and AC connections, fibre-optic cables and control lines.
Due to the dimensions of the installation, the steel trusses are also designed accordingly. In addition, cable trays for the customer’s lightning protection system are integrated into the structure.
Integration into the existing wastewater treatment infrastructure
One of the project’s particular challenges is integrating a photovoltaic system of this size into the existing wastewater treatment infrastructure while operations continue.
The steel structure is installed directly around the existing tanks, with the existing tank structures also being incorporated into the technical implementation. At the same time, supports and trusses, drive units, suspension and traction cables, as well as the entire electrical infrastructure, must be precisely coordinated.
The project therefore demonstrates the technical possibilities that arise when existing infrastructure is incorporated into the planning of a large-scale photovoltaic system from the outset.
The system has been taking shape since June
Since construction began on 8 June 2026, the project has been progressing step by step.
Work completed and currently under way includes drilling and anchoring, installation of the supports, and pre-assembly and erection of the large steel trusses. In parallel, motors and traction cable deflection units are being installed, cable trays and generator junction boxes are being mounted, and the suspension and traction cables are being prepared.
The next steps include installation of the folding roof groups and further electrical integration.
Commissioning is scheduled for January 2027. Once successfully completed, the approximately 2.75 MWp installation will become Germany’s largest solar folding roof.
A major project is a team effort
A project of this scale is only possible through the cooperation of numerous disciplines and partners.
The client and project owner is the City of Stuttgart, represented by the Civil Engineering Office and the municipal wastewater utility Stadtentwässerung Stuttgart (SES). The technical implementation of the solar folding roof is being carried out by dhp Technology AG.
Other companies involved in the project include:
- Peter und Lochner
- SSIFT
- Weber Ingenieure
- Weisske und Partner GmbH beratende Ingenieure
- Tüfer Gebr. GmbH as the executing construction company
- Good Elektro GmbH as executing electrical installer
A big thank you to everyone involved in the project for their cooperation and contribution to the implementation of this exceptional installation.
Stuttgart-Mühlhausen is therefore not only becoming home to Germany’s future largest solar folding roof. The project also demonstrates the potential of large existing infrastructure sites when energy generation, plant operation and structural conditions are considered together.
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