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Pumped storage power station capacity increase investigated

As part of the construction of the underground pumped storage power station between the Emosson and Vieux-Emosson dams, Nant de Drance SA is examining the possibility of increasing the installed capacity from 600 to 900 MW. The main reason is the growing need for control and peak energies, and the increase in capacity would also involve the raising of the Vieux Emosson dam by 15 to 20 metres. The project design work and environmental impact studies will be carried out in 2010, as the Nant de Drance building work continues. The decision about this adjustment to the initial project will be made at the end of 2010.

The Nant de Drance project involves the construction of a 600 MW underground pumped storage power station between the Emosson and Vieux-Emosson dams. It represents an investment of CHF 990 million by the Nant de Drance SA shareholders, Alpiq (54%), SBB (36%) and FMV (10%). Having begun in the spring of 2008, the work is proceeding according to schedule with the digging of the tunnels to access the caverns. The construction work on the underground powerhouse and pressure shaft between the two dams will begin in the spring of 2011, once the access tunnels are complete.

Pumped storage power station: an essential complement to the development of the new renewable energies and to meet the growing need for peak energy Given the increase in peak consumption demand, the peak energy supplied by the hydropower schemes must be increased in order to ensure a secure supply for the Swiss electricity grid, as well as for the SBB railway network and that of the private railways supplied by the SBB. Moreover, pumped storage power stations meet the increased need for control energy, in other words, the energy needed to ensure a balance at all times between the energy produced and the energy consumed in the network. The higher demand for control energy on the European markets can be explained mainly by the growth in the new renewables such as wind and solar power. These schemes, which are directly dependent on the weather, have an irregular generating pattern that must be topped up by control energy. The pumped storage power stations, with their dams - a real reserve of energy that can be injected into the grid at any time - offer an immediate and effective solution to make up for these decreases in generation.

Preliminary project investigation: 900 MW capacity instead of the planed 600 MW In March 2009, Nant de Drance SA launched a preliminary project aimed at examining the possibility of increasing the capacity of the pumped storage power station from 600 to 900 MW, by adding two additional generating sets of 150 MW each to the four sets initially envisaged. The feasibility study carried out this year shows that the adjustment to the scheme would be possible under the present configuration and timetable of the project. The volume of water retained by the Vieux-Emosson dam would have to be increased to 23 to 26 million m3, or raising the dam by 15 to 20 metres. This adjustment to the Nant de Drance project would require a minor change to the current terms of the concession, and a building permit for the raising of the Vieux-Emosson dam and the re-sizing of the caverns and the hydraulic system. The decision will be taken by Nant de Drance SA at the end of 2010, once the detailed studies of the project and its environmental impact have been completed.

Remarks: Further information about the project can be found at or obtained by emailing