Another 20 metres for the Vieux-Emosson dam

Work to raise the height of the Vieux-Emosson dam by 20 metres has just been completed with the pouring of the final concrete block. This work was carried out as part of building the Nant de Drance pumped storage power station. It enables the storage capacity of the Vieux-Emosson reservoir to be doubled, thereby ensuring sufficient flexibility to benefit fully from the future station's installed capacity of 900 MW. Commissioning of the power station is planned for the end of 2018. It will make a significant contribution to Switzerland's new energy strategy.

In order to ensure sufficient flexibility and to benefit fully from the capacity of the future Nant de Drance pumped storage power station, the height of the Vieux-Emosson dam has been raised by 20 metres. 475 concrete blocks 1.5 metres high by 12 metres wide, i.e. 68,000 m3 of concrete, have thus been added to the original dam, 20 metres of the upper section of the dam first having to be demolished. This work to raise its height, started in the spring of 2013, was finished on 25 September 2014. The Vieux-Emosson dam now measures 76.5 metres high and 205 metres long at the top. The reservoir's storage capacity has thus been doubled, reaching 25 million m3, which equates to approximately 20 hours of turbine operations. Some finishing work, such as injection work to guarantee that the dam is water-tight, will need to be carried out in 2015 before the reservoir is filled.

Other work on the Nant de Drance site is progressing as planned. Excavation of the machine cavern was finished in March 2014 and preparations for the installation of the six groups of pump turbines have also started. Drilling of the second vertical shaft was completed in June and installation of liners is underway in various sections. The power station will become operational in stages starting in 2018.

An essential tool for security of supply

With a total power capacity of 900 MW, the six groups of pump turbines at Nant de Drance will enable the generation or storage of large quantities of energy at very short notice, according to needs. When electricity demand is high, water stored in the Vieux-Emosson dam upper reservoir will be turbined to generate energy. Conversely, when electricity demand is low, water from the Emosson reservoir will be pumped to the Vieux-Emosson reservoir for storage of the energy.

The future Nant de Drance power station is very well suited to the Swiss Federal Council's energy strategy. Electricity generation and electricity consumption can be balanced by providing balancing energy. This is particularly important, considering the growing, irregular production of electricity from new renewable energies. Nant de Drance will make an important contribution to the stability of the European electricity grid and to Switzerland's security of supply.

The shareholders – Alpiq (39%), SBB (36%), IWB (15%) and FMV (10%) – are investing nearly 1.9 billion Swiss francs in its construction.

For further information on Nant de Drance: www.nant-de-drance.ch