Wynau Hydroelectric Plant

The 100 year-old power plant Wynau operated by Onyx Energie Mitteland AG had to be replaced by a new installation. The latter consists mainly of a power house with two turbines and a weir system as well as a 2'900 m long pressure gallery, enabling one of the turbines to benefit from a higher fall. The realisation had to be carried out in two stages. The first stage, comprising the power house with the Aare turbine at the weir, was put into service on schedule in April 1996. The second stage comprises essentially the gallery, the underground surge chamber and the discharge unit.

Main Data

  • Turbine-discharge: 2 x 220 m³/s
  • Power
    • Aare turbine: 12 MW
    • Tunnel turbine: 16 MW
  • Annual energy generation: 139 GWh
  • Rise in output: 70 % (relative to the previous installation)
  • Gallery
    • Length: 2'900 m
    • Profile: circle ∅ 10.7 m
    • Excavation: by TBM
    • Geology: deep sweet water molasse


Onyx Energie Mitteland Ltd., Langenthal


IUB Engineering Ltd.

Construction period


Construction costs

96.065 mio. CHF

Scope of services

Feasibility studies

Preliminary project, cost estimate

Monitoring the hydraulic model tests at VAW (Laboratory of Hydraulics, Hydro-logy and Glaciology, ETH-Zurich)

Tender documents, contracts

Civil works

Hydromechanical equipment, cranes

Turbine, generator


Other works

Realisation stage 1

General supervision of project and works

Site supervision

Detailed design of the civil and electromechanical project

The quality management process was set up for the first time at IUB on the basis of this project in view of obtaining the ISO 9001 Certificate. The process was tried out and experience with quality management was gained internally as well as in conjunction with the contractors. In 1995 IUB was amongst the first engineering consultants to be awarded the ISO 9001 Certificate.