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The plant

The Nant de Drance power plant has a capacity of 900 MW, making it one of the most powerful pumped storage plants in Europe. It is located 600 meters underground, between the Emosson and Vieux Emosson reservoirs, and has a storage capacity of 20 million kWh. The plant offers flexible power generation, playing a key role in stabilising the electricity grid throughout Europe and in safeguarding Switzerland’s power supply.

How it all works

Please activate the subtitles to see the infographics’ explanations.


Key figures


the capacity of the Nant de Drance plant, which is equivalent to that of the Gösgen nuclear power plant


the number of Francis turbines, each with a capacity of 150 MW


million kWh
the plant's storage capacity corresponding to the capacity of 400,000 electric car batteries

No. 2

Emosson Lake is currently the second-largest reservoir in Switzerland, after Grande Dixence, and its 180-metre-high dam is the country’s fifth tallest
Less than


the time needed for the power plant to stop pumping at full speed and start turning the turbines at full speed; and less than 10 minutes to switch from turbine mode to pump mode.
More than


the plant's yield, which is currently one of the highest for a pumped storage power plant


million m3
the capacity of the Vieux Emosson, which is more than 6,500 Olympic-sized swimming pools


the water in the Emosson reservoir comes from both Switzerland and France


the height of the two vertical penstocks that connect the Vieux Emosson and Emosson reservoirs – that's 100 m higher than the Eiffel Tower (324 m)


the diameter of the two penstocks


the length of the underground turbine chamber, which is equivalent to two football fields


the time needed to empty out the Vieux Emosson reservoir


the total length of the underground galleries within the Nant de Drance plant

Power house cavern

Pump turbine

Vieux Emosson dam

Protecting the environment

One of the priorities of Nant de Drance and the licensing authorities is to reduce environmental impact as much as possible. Fifteen projects at a total cost of twenty-two million Swiss francs have been, or will soon be, completed to offset the environmental impact of the following constructions: pumped storage power plant and very high-voltage line connecting the power plant to the power grid.

The work is managed by Nant de Drance SA and monitored by an advisory group represented by WWF, Pro Natura, the public authorities concerned, the canton of Valais as well as the Swiss Federal Office of Energy.

Compensation measures

Most measures aim to recreate specific biotopes locally, especially wetlands, in order to encourage recolonisation of the area by certain rare or endangered animal and plant species in Switzerland.

  • Four measurements are being carried out on the site perimeter. They concern four areas – located in Châtelard, in Bierle (municipality of Trient), at the Gueulaz pass and at the foot of the Vieux-Emosson dam - used in particular to store the excavated material from the tunnels and caverns. Nant de Drance is rehabilitating these areas and creating environments that encourage biodiversity. It is also planned to create an educational trail in Châtelard.
  • The Salanfe SA’s overhead power line, located between the Miéville plant and Salanfe, has been installed below grade because it was dangerous for birds.
  • In Salvan, pastures have been reopened following brush-clearing work. Wet biotopes will also be created. This measure is carried out in collaboration with farmers and breeders from the region and enables to support mountain agriculture.
  • The wetland of the Fond du Mont in Vernayaz, which had been drained, has been refilled with water, in collaboration with the municipality. As part of this project, the Lantze Canal will undergo renaturation, and downstream, in Miéville, small lakes will be created along the River Salanfe.
  • In Vernayaz, the bed of the Trient River will be widened by relocating the existing dyke between the SBB bridge and the motorway bridge in order to create an alluvial zone and give more space to the river. Additionally, specific biotopes will be developed set back from the bed of the River Trient.
  • In the municipality of Dorénaz, work is being carried out as part of a project to secure the stream in Alesse and a wetland has been developed along the right bank of the Rhône.
  • From the mouth of the Trient to the Dorénaz bridge, the bed of the Rhône will be widened to give it more room to expand, particularly in the event of flooding. Considered a priority, this measure is being carried out during the 3rd Rhône correction with the financial participation of Nant de Drance SA.
  • Going up the Rhône in the direction of Martigny, the so-called “Lac des Sables” measure will consist of reclaiming a gravel quarry lake and creating wetlands.
  • In the municipality of Martigny, biotopes have been developed in the forest along the Bienvenue Canal in order to increase the amphibian population, or more specifically, yellow-bellied toads.
  • In Saxon, as part of a project to secure the municipality’s canals, Nant de Drance SA has completed the widening and regeneration of these canals in order to promote biodiversity.
  • Nant de Drance, in collaboration with WWF, is managing an on-going project to eliminate invasive plants, such as Japanese knotweed, which have colonised the banks of the Trient.

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Overhead travelling cranes
Alternator engine
Main inlet valve
Pump turbine
Main spherical valve
Drainage channel
Main inlet valve
  • inner diameter: 2,100 mm
  • nominal design pressure: 65 bar
  • weight: approx. 120 t
Pump turbine
  • maximum power: 157 MW
  • max. flow rate: 60 m3/s
  • nominal speed: 428.57 rpm/min
  • wheel diameter: 3,557 mm
  • wheel weight: 18.3 t
Main spherical valve
  • inner diameter: 2,800 mm
  • nominal design pressure: 35 bar
  • weight: approx. 135 t
Draft tube
Veudale pump station
Dam entry
Bottom outlet
Upper gallery
Middle gallery
Lower gallery
Drainage shaft
Access shaft
Winter access
Observation station
Frequency converters
Phase inverters
Circuit breakers
Machine control system
Cooling circuit
Draft tube