ARA Grenchen (SO): Foldable Solar Roof Turns Clarification Basins into Power Plants

Summary:
A state-of-the-art foldable solar roof spans the clarification basins of ARA Regio Grenchen. With an installed capacity of 890.96 kWp, 46 folding roof tracks, and 2,072 modules, the system generates around 750 MWh of solar power annually—making use of an area that was previously unused. Commissioning took place in March 2024, with final acceptance on June 6, 2024. This makes Grenchen one of the largest dhp installations of its kind.

Background & Objective

ARA Regio Grenchen aimed to significantly reduce its electricity consumption without compromising the primary function of the basins. This is where the HORIZON foldable solar roof demonstrates its strengths: secondary use of space above existing basins, large support spacing thanks to lightweight construction, and fully automated folding and unfolding depending on weather conditions.

The Solution: HORIZON Above the Clarification Basins

The Grenchen project consists of two system sections (including above biological and primary clarification basins). The folding mechanism on tension and support cables enables large spans, protects the modules during storms, hail, and snowfall through automatic retraction, and remains operational via an uninterruptible power supply (UPS) even in the event of a power outage. This ensures uninterrupted operation of the ARA at all times.

Implementation & Project Timeline

  • Construction period: November 2023 – April 2024
  • Commissioning: March 2024
  • Final acceptance: June 6, 2024
    Additionally, an independent acceptance inspection was carried out on May 28, 2024.
  • Client/Representation: ARA Regio Grenchen, represented by Benno Schläfli
  • Design author: dhp technology AG
  • Public perception: The project attracted significant media attention (including SRF “Schweiz Aktuell”) and was internally recognized as the “largest realized foldable solar roof to date” (as of September 2024).

Impact & Added Value

  • High self-sufficiency: Expected approx. 750 MWh/year—a substantial contribution to the plant’s energy supply.
  • Zero additional land use: 7,385 m² of covered area above existing infrastructure makes efficient use of idle space—without hindering basin operations.
  • Built-in operational safety: The system automatically retracts in high winds, hail, or snowfall; the UPS ensures retraction even during power outages.

Project Factsheet

  • Location: Grenchen (SO), Archstrasse 68
  • System: HORIZON foldable solar roof (foldable modules on support cables)
  • Installed capacity: 890.96 kWp
  • Expected annual output: ~750 MWh
  • Covered area: 7,385 m²
  • Folding roof tracks: 46
  • Number of modules: 2,072
  • Construction period: 11/2023–04/2024
  • Client: ARA Regio Grenchen

Why This Reference Stands Out

  • Innovation: Folding mechanism with weather-adaptive control instead of a static PV canopy.
  • Visible sustainability: Generating power where it’s needed—without sealing additional land.
  • Scalability: Modular system; adaptable to different basin layouts.