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
