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Further step towards an increase in the capacity of the pumped storage power station

Whilst the construction work on the underground pumped storage power station between the Emosson and Vieux-Emosson dams continues, Nant de Drance SA has launched the public display concerning the change to the concession and the building permit for the Nant de Drance Plus project. The plan is to increase capacity of the plant from 600 to 900 MW by adding two 150 MW sets to the four turbine sets originally planned.

Just over 30 days after the announcement of the public display of the Nant de Drance Plus project was published in the Swiss official gazette, the Bundesblatt dated 11 May 2010, four objections have been lodged. Three are from municipalities and concern the compensation arrangements, whilst the fourth has been issued by the société des pêcheurs du Vieux Emosson (Company of Fishermen of Vieux Emosson) which is asking for an additional study. Nant de Drance SA, a company owned by Alpiq (54%), SBB (36%) and FMV (10%), has already begun discussions with the parties concerned in order to find a satisfactory solution for everyone as quickly as possible.

An adjustment that is achievable as part of the current construction work

The Nant de Drance project provides for a 600 MW underground pumped storage power station to be built between the Emosson and Vieux-Emosson dams. With the Nant de Drance Plus project, the installed capacity could be increased to 900 MW by adding two further 150 MW sets. The volume of water retained by the Vieux-Emosson dam would be increased to 23 to 26 million m3 by raising it from 15 to 20 metres. This adjustment could be done as part of the current Nant de Drance project without delays to the timetable. Because the small environmental impact would be fully offset by practical measures, only a minor modification to the present concession and a building permit for the raising of the dam and the re-sizing of the underground chambers and the hydraulics system would be required. The final decision as to whether to implement the project or not will be made by Nant de Drance SA at the end of 2010. If the work is to be done, it could then be included in the current building project.

A concrete response to the growing need for peak and balancing energy

Given the increased demand at peak consumption times, the peak energy supplied by the hydropower schemes will have to be further developed in order to ensure a secure supply for the Swiss electricity grid, the SBB network and the private railway networks that take their supply from the SBB. Furthermore, pumped storage power stations are an answer to a growing demand for balancing energy, that is, the power needed to ensure that the energy consumed through the grid is balanced at all times by the energy generated. The main reason for the increased demand on the European markets is the growth of new renewable energies such as wind and solar power. These schemes - directly dependent on weather conditions - have an irregular generating pattern that must be topped up by balancing energy. Pumped storage power stations, with their dams, represent a real stock of renewable energy that can be injected into the grid at any time, offering an immediate and effective solution to fill the gaps when production dips.

Progress of Nant de Drance construction work

After the installation of the tunnelling equipment last winter, work is in progress to dig the access tunnel to the underground chambers at an altitude of 1700 m above the municipality of Finhaut.  It will take a total of 18 months to complete this 5.6 km underground gallery. From the end of 2010, work will begin on the excavation of the underground chambers and hydraulic conduits. The plant will gradually be brought into service as scheduled from 2016.

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