Pumped-storage station (PSH)

In brief

In French, STEP stands for Station de Transfert d'Énergie par Pompage (pumped-storage station). It is like a giant battery: electricity is stored in the form of water held high up, and recovered when it is needed.

How does it work?

A pumped-storage station has two reservoirs at different altitudes: one high up, one low down.

1. When there is surplus electricity (at night, or in full sun when solar panels produce a lot): pumps lift the water from the lower lake to the upper lake. The extra electricity is put aside!
2. When there is a shortage (for example at 7 p.m. in winter, when everyone switches on the light): the gates are opened. The water comes back down and spins turbines, which make electricity in less than 3 minutes.

Key facts

• Pumped-storage stations are one of the main ways to store very large amounts of energy.
• Grand'Maison (Isère): the most powerful in Europe, 1,800 MW.
• Revin (Ardennes): 800 MW.

Words to know

• MW (megawatt): a unit of power. 1 MW is 1,000 kW, the power of about 1,000 radiators of 1 kW.
• Efficiency: what you get back compared with what you put in.

Did you know? The idea is not new: the first pumped-storage stations were built in Italy and Switzerland at the end of the 19th century, more than 120 years ago!

Going further

A pumped-storage station does not create energy: it uses some to pump the water uphill, then recovers about 70 to 80% of it when the water comes back down. What it brings is the ability to store very large amounts of electricity, for hours, and give them back when the grid needs them.