The pumped storage power 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 metres underground, between the Emosson and Vieux Emosson reservoirs, and has a storage capacity of 20 million kWh. Thanks to its highly flexible power generation, it plays a key role in stabilising the electricity grid throughout Europe and safeguarding Switzerland’s power supply.
How it all works ?
Key figures
Facilities at the pumped storage power plant
Water is passed through the turbines when electricity requirements are high, to meet demand peaks. When there is less demand for electricity or production from new renewable energies exceeds demand, water is pumped from the lower dam to the upper dam in order to store the energy.
Operating diagram
Water stored in the upper dam is passed through the turbines when electricity requirements are high, to meet demand peaks. When there is less demand for electricity or production from new renewable energies exceeds demand, water is pumped from the lower dam to the upper dam in order to store the energy.
Vieux Emosson reservoir

Vertical penstocks

Caverns (power house and transformer)

Water ways

Emosson reservoir

Access tunnel to upper part of the plant

Main access tunnel from Le Châtelard


Power house cavern
The power house cavern is located 600 metres underground, between the Emosson and Vieux Emosson reservoirs. It is the heart of the plant.
Overhead travelling cranes

Motor-generator

Spherical inlet valve

Pump turbine

Spherical outlet valve

Drainage channel

Ventilation

Frequency converters

Phase inverters

Circuit breakers

Machine control system

Cooling circuit

Suction pipe


Pump turbine
The Nant de Drance plant comprises six pump turbines, each with a capacity of 150 MW.
Spherical inlet valve

Interior diameter : 2,100 mm
Nominal design pressure : 65 bar
Weight : approx. 120 t
Pump turbine

Interior diameter : 2,100 mm
Nominal design pressure : 65 bar
Weight : approx. 120 t
Spherical outlet valve

Inner diameter : 2800mm
Nominal design pressure : 35 bar
Weight : approx. 135 t
Suction pipe


Vieux Emosson dam
The Vieux Emosson dam is located at an altitude of 2,225 metres. It has a storage capacity of 25 million m3 of water, which corresponds to 20 million kWh of energy.
Spillway

Veudale pump station

Bottom outlet

Pendulums

