No abstract

As the demand for electrical energy in Europe is constantly increasing, particularly at peak times, the pumped storage power station under construction at Nant de Drance in the canton of Valais has assumed a central position in the new Swiss energy policy. This power station represents an ideal means of storing large quantities of energy, which is generated more and more from wind and solar with their unreliable delivery dependent on meteorological conditions. This 900 MW project is mostly being constructed underground and fits optimally into an existing hydropower complex. A system of tunnels about 15 km long is being constructed for access to the plant, including the 5.5 km and 9.5 m diameter long main access tunnel, which is being driven by a tunnel boring machine. In parallel to the underground works, the Vieux Emosson dam is being raised by 20 m, which will double the storage capacity of the headwater reservoir.The core components of the plant are the six 150 MW variospeed Francis pump-turbines, which will be housed in a machine cavern 184 m long, 52 m high and 32 m wide. Immediately next to the machine cavern are further caverns for the transformers and the gas-insulated switchgear.The investment costs for the entire project are about 1.8 billion CHF plus interest. Construction works started in 2008 and the six pump-turbines should start operation in stages in 2016 to 2018.