At the Birmensdorf wastewater treatment plant, the key question was not whether solar power should be produced, but how it could be integrated under real operational conditions. Critical requirements included permanent access to the tanks, the ability to carry out revisions, and uninterrupted day‑to‑day plant operation.
For this reason, the Birmensdorf Wastewater Treatment Association opted for a solution that technically integrates energy generation into existing processes rather than competing with plant operation.
A HELIOFLEX® foldable solar roof was installed above the primary and aeration tanks. The system is divided into three fields with a total of five foldable roof sections, spanning around 1,900 m² of existing tank surface area.
This configuration allows individual sections to be moved as required and ensures unrestricted access to the tanks at all times – both for maintenance and for overhead revision work. The system’s movability was a decisive factor in approving the project.
The HELIOFLEX® system has an installed capacity of 374.4 kWp, resulting in an annual solar power generation of approximately 370,000 kWh. A large share of the electricity is consumed directly on site, significantly increasing the plant’s self‑consumption rate.
Overall, the system covers around 30 % of the Birmensdorf plant’s electricity demand. For a continuously operated 24/7 infrastructure, this means a noticeable reduction in external electricity purchases and greater independence from energy price fluctuations.
Local solar power generation at the site reduces emissions by approximately 35–40 tonnes of CO₂ per year. These savings are achieved exclusively through the use of already sealed infrastructure surfaces – without any additional land use or new construction.
The Birmensdorf project demonstrates how the HELIOFLEX® foldable solar roof can be integrated as a functional part of existing infrastructure. The focus was not on maximum output or landmark size, but on a solution that works reliably in daily operation, remains fully serviceable, and delivers long‑term energy benefits.
As a result, the solar roof becomes an integral extension of plant operations – and the Birmensdorf wastewater treatment plant a practical example of how solar power can be implemented under real operational conditions.