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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.

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