Nant de Drance
Nant de Drance SA is building a pumped storage power station in the Valais municipality of Finhaut. The facility will be situated in an underground cavern between the existing Emosson and Vieux Emosson reservoirs. The power station is designed to generate electricity at peak consumption times and to balance out the irregular and variable electricity generation from renewable energy sources.
When electricity consumption is high, the water from the Vieux-Emosson reservoir plunges down two 425 metre high vertical shafts into the underground power station. Here it drives turbines and is subsequently fed into the Emosson reservoir. In reverse, when the demand for electricity is reduced the water from the Emosson reservoir is pumped back up to the Vieux-Emosson reservoir. Hence the Nant de Drance power station is able to store the energy from the excess generation. With an output of 900 megawatts, the Nant de Drance power station will generate around 2.5 billion kWh of energy per year.
Progress with construction work
Work on excavating the underground machine cavern has been under way since mid-2012. The dimensions are impressive: 194 meters long, 52 meters high and 32 meters wide. The excavation was completed in March 2014. The work to raise the height of the Vieux-Emosson dam was started in the spring of 2013. After completion of the construction work, which will take another two years through to the autumn of 2015, the dam will have gained 20 meters in height. The structural steelwork and the installation of the machines will be started in 2014. The power station will become operational in stages starting in 2018.
6 Francis pump turbines