29 October 2026
Today, the City of Stuttgart presented the latest construction progress of Germany's largest folding solar roof at a major press event. As the technology partner, dhp Technology was also on site and pleased to see the strong interest in this exceptional project.
Germany's largest HELIOFLEX folding solar roof is currently being built at the Stuttgart-Mühlhausen Main Wastewater Treatment Plant. Covering an area of approximately 17,500 square metres, the innovative photovoltaic system is being installed above the aeration tanks used for biological wastewater treatment. With an installed capacity of 2,745 kWp, it will also become the largest photovoltaic installation in the City of Stuttgart.
Today's press event provided an opportunity to present the project, its current construction progress and the specific technical challenges involved. Together with Stuttgart's municipal wastewater utility, dhp Technology is demonstrating how existing infrastructure can be intelligently used to generate solar energy.
A total of 5,280 solar modules will be installed across 120 movable folding roof sections. The modules are suspended from steel cables and can be automatically retracted in the event of strong winds, snow or hail.
The structure is positioned approximately five metres above the aeration tanks, ensuring that the facilities below remain accessible for ongoing wastewater treatment operations and maintenance work. This enables the existing infrastructure to serve a dual purpose without requiring additional land.
Following its planned commissioning in the second quarter of 2027, the HELIOFLEX folding solar roof is expected to generate more than 2.2 million kilowatt-hours of solar electricity per year. This will cover approximately nine percent of the wastewater treatment plant's electricity requirements.
The electricity generated will be used directly on site, particularly for the energy-intensive biological wastewater treatment process. This will reduce the need for electricity from the grid and make an important contribution to a more sustainable energy supply.
Installation work on the system has been underway since June 2026. Integrating the approximately 250-tonne steel structure into the existing infrastructure requires careful planning and close coordination among all project partners.
Lars Färber, Chief Operating Officer of dhp Technology, highlights the significance of the project:
"The challenge lies in integrating a photovoltaic system of this scale into the infrastructure of an operational wastewater treatment plant. The project demonstrates the enormous potential of existing large-scale infrastructure when energy generation, plant operations and structural requirements are considered together."
The Stuttgart-Mühlhausen project is another example of how existing infrastructure can be intelligently used to support the energy transition.
Further information about the project is available from Stuttgart's municipal wastewater utility.