After more than six years of construction work, the Fionnay and Nendaz hydropower plants, as well as the waterfall that connects Lac des Dix to these two power plants, have been partially recommissioned. This is nine months ahead of the original schedule, which means that the facilities are available at a time when Switzerland is in particular need of electricity.
Almost 60 years after the commissioning of the Grande Dixence facility, the hydroelectric company has undertaken major renovation and maintenance work on the entire waterfall that links the Lac des Dix to the Rhône plain. Grande Dixence SA and its shareholders are investing a total of CHF 240 million to carry out this major work. Renovation work at the six production units of each of the two power plants at Fionnay and Nendaz has been undertaken on the valves, turbines, alternators, automatic control systems and auxiliary services. Following the discovery of micro-cracks in the lining, the overhead part of the penstock, i.e. an 850-metre section located between Péroua and Condémines, has been replaced, while the anti-corrosion protection of the underground sections has been renovated. The safety valves located at Louvie and Péroua, at the start of the penstocks, have been renewed and the valves located at the start of the water supply tunnels, at the Grande Dixence dam and at the Fionnay basin, have also undergone major renovation work.
Construction site installations at the top of Fionnay with the Mauvoisin dam in the background, November 2020 © Alpiq
Construction site installations at Louvie, November 2020 © Alpiq
Dismantling the Péroua - Condémines penstock, July 2020 © Michel Martinez
Construction of the new Péroua - Condémines penstock, May 2021 © Michel Martinez
Assembly of the valve in Louvie, June 2022 © HYDRO Exploitation
Expedited return to service
The replacement of the Péroua – Condémines overhead penstock, which began at the end of 2019, was completed seven months ahead of schedule – despite the constraints caused by the COVID-19 pandemic. The pipeline was reopened in early September 2022. The completion of this essential phase accelerated the planning of the other works in progress. Thanks to their commitment, the Alpiq and HYDRO Exploitation teams in charge of the work were able to overcome the challenges of the shortened schedule and solve the problems inherent in such work in a timely manner. As a result, four of the six units at each of the Fionnay and Nendaz power plants were brought back into service on 13 January 2023. Originally planned for the third quarter of 2023, this partial recommissioning has enabled the power plants to contribute to Switzerland's electricity supply when it is most needed, during the winter months. The entire facility, with an installed capacity of around 700 MW, will be back in service by the end of 2023.
Storage production guaranteed despite the work
A special feature of the Grande Dixence complex is that a second waterfall links the Lac des Dix to the Rhône plain. This waterfall feeds the Bieudron power plant, the most powerful hydropower plant in Switzerland with 1200 MW. Consequently, all of the water stored in the Grande Dixence dam was able to be turbined by the Bieudron power plant while the works were being carried out. One of the largest hydroelectric complexes in Switzerland was thus able to supply Switzerland with electricity without interruption.