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The Nant de Drance project enters a crucial phase in 2012

2012 promises to be a busy year at the Nant de Drance construction site. Tunnelling will be completed in the summer, while excavation of the main cavern will continue. Work on raising the Vieux Emosson dam is scheduled to begin in late spring. Over 250 people will be working at the construction site in 2012.

The tunnel boring machine, which started excavating from Châtelard at the beginning of 2010, will break through the last few metres of the principal gallery leading to the machinery cavern in summer 2012. This colossal machine, which is 142 metres long with a diameter of 9.45 metres, has already tunnelled 4 km of the total gallery length of 5.6 km. At present, it is located 180 metres beneath the bed of the Emosson reservoir and advancing at a rate of 10 to 20 metres per day. Once the machine has completed its mission, it will be dismantled and the various pieces shipped back to the lowlands by special transport.

Excavation of the machinery cavern will continue throughout 2012. This cavern is designed to house six pump turbines, each with a capacity of 150 MW. This part of the work is operated from the access tunnel to the machinery cavern. Work had to be suspended at the end of November due to snow. In order to resume the excavations as rapidly as possible, workers began to clear the road of snow in the middle of January. A total of 170,000 m3 of rock needs to be blasted away in order to construct this cavern, which will be 50 metres high, 30 metres wide and 170 metres long. Excavation is expected to be completed by spring 2014.

Emptying the Emosson reservoir between February and May will also facilitate the work on the Nant de Drance project. This unprecedented move will allow the workers to access the water intake assembly submerged in the Emosson reservoir in September 2011 and to prepare the platform for a second, similar structure to be submerged in autumn 2012. The power station will then be able to pump water from the Emosson reservoir into the Vieux Emosson reservoir and, likewise, to allow water to flow back into the Emosson reservoir after passing through the turbines.

Finally, the preparations for the raising of the Vieux Emosson dam will also begin this year. In effect, the dam will be raised by 20 metres in order to double the storage capacity of the reservoir. In springtime, access to the construction site will be prepared and the first installations erected. From June to October, the existing crest will be demolished by blasting. Throughout 2012, access to the dinosaur tracks, a popular tourist attraction, will be redirected via the Veudale Gorge. The public footpath alongside the Vieux Emosson reservoir will be closed, but hikers will still be able to reach the Vieux Emosson Hut throughout the summer.

An indispensable resource for Switzerland's new energy policy Owing to the new energy policy laid down by the Federal Council, the Nant de Drance pumped storage power station, a project initiated by Alpiq, will in future be one of the key resources for meeting the growing demand for balancing energy ensuring that the energy consumed through the grid is balanced at all times by the energy generated. The main reason for this increased demand in Switzerland and Europe is the expansion of new renewable energies, such as wind and solar power. Since these facilities are directly dependent on weather conditions, they have an irregular generating pattern that has to be topped up by balancing energy. Since pumped storage hydroelectric power stations represent a real stock of renewable energy that can be injected into the grid at any time, they offer an ideal complement to these new, more irregular energy forms, production of which is more irregular.

In order to allow the energy that will be produced at Nant de Drance to be transported and to secure the country’s electricity supply, the Swiss high-voltage grid and particularly the Valais grid will have to be upgraded. The Federal Council has in fact described the extension of the grid as being “imperative for Switzerland’s future production infrastructure”.

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