Nant de Drance pumped storage power station

In the effort to secure electricity supplies even at times of peak demand, Atel and SFR Swiss Federal Railways are planning the Nant de Drance pumped storage power station, to be built underground in the lower Valais region. In the period up to 2015, the partners are intending to invest around 700 million Swiss francs in the production of flexibly available peak energy from Swiss waterpower. The two companies will decide whether to firmly commit and go ahead with construction after detailed plans are complete in late 2007.

Electricity for consumption peaks

Nant de Drance Media Conference, 20 June 2006

In the effort to secure electricity supplies even at times of peak demand, Atel and SFR Swiss Federal Railways are planning the Nant de Drance pumped storage power station, to be built underground in the lower Valais region. In the period up to 2015, the partners are intending to invest around 700 million Swiss francs in the production of flexibly available peak energy from Swiss waterpower. The two companies will decide whether to firmly commit and go ahead with construction after detailed plans are complete in late 2007.

The project involves building a pumped storage power station in an underground cavern between the existing Emosson and Vieux Emosson reservoirs, a pair of lakes located within the border community of Finhaut, between Martigny and Chamonix in the canton of Valais.

The power station will be designed to generate electricity at times of peak consumption. With an average 300-metre height difference between the two reservoirs, water from Vieux Emosson will pass through turbine-generators on its way down to Emosson. Water will be pumped back from the lower to the upper reservoir at night and at weekends, when electricity is less in demand.

Equipped with 600-megawatt turbines and pumps, the Nant de Drance power station is expected to generate around 1,500 million kWh of peak energy a year. The pumps will require some 1,800 million kWh of off-peak energy. The cavern to house the power station lies deep under rock at an altitude of 1800 metres, with access via a tunnel five kilometres long. The tunnel entrance is in the valley, adjacent to the Le Châtelard power station operated by the SFR. 50-hertz energy passing through cables in the access tunnel and an existing string of electricity masts will feed into the 380 kV grid at Martigny.

Emosson is an ideal site for building a pumped storage facility: the two reservoir lakes are fairly adjacent as viewed from above, yet there is a large height difference between them. The power station can be started up and running at full output in less than two minutes. This kind of flexibility is a strong point of Nant de Drance, making it ideal for compensating differences between alternating periods of peak and reduced demand.

The facility will represent a significant contribution to the security of public electricity supplies by helping to meet the growth in peak demand and further heavy consumption peaks associated with railway operations. When it comes to meeting national energy requirements, it must be noted that the demand for peak period energy can be expected to increase in a similarly strong fashion to that of overall demand. With increased numbers of train connections being introduced, the power needed to keep Switzerland’s railways running on a steady basis is set to increase by as much as 65 percent over the next 20 years.

The pilot project for the pumped storage power station was concluded in August 2005. Detailed project planning will continue until late 2007, after which Atel and SFR expect to decide on a construction go-ahead. The investment sum involved is estimated at around 700 million francs, with operation expected to commence in 2014.

Further information / download press kit: www.nant-de-drance.ch