ENERGY SECURITYSwiss “Water Battery” Boosts Europe's Energy Storage Plans

By Jo Harper

Published 1 December 2022

A Swiss company has built what is being called a giant water battery deep under the Alps that provides an energy storage capacity equivalent to 400,000 electric car batteries. It could be a game changer.

A 2-billion-Swiss franc (€2.05 billion/$2.10 billion) project could help stabilize Europe’s increasingly expensive electricity as it shifts to renewable energy.

The so-called water battery, Nant de Drance, located between two reservoirs in a cave 600 meters (nearly 2,000 feet) underground in the Swiss canton of Valais, is being described as a big step in Europe’s transition to green energy. Europe will need to develop 200 gigawatts of energy storage capacity by 2030 — more than fourfold its current capacity, the European Association for Storage of Energy estimates. 

The project, which took 14 years to finish, is made up of 17 kilometers (10.5 miles) of underground tunnels, housing six huge turbines powered by water cascading down a steel pipe in a cavern the length of two football fields. At the peak of construction, 650 workers were on-site, working to excavate some 1.5 million cubic meters of mountain rock at an altitude of 2,000 meters.

The project involved raising the water level of one of the two reservoirs, the upper one (Vieux-Emosson) by 21.5 meters to double its capacity. It now holds as much water as 6,500 Olympic-sized swimming pools (25 million cubic meters of water).

Crucially to its success, Nant de Drance uses variable speed pump turbines, said Pascal Radue, CEO of GE Renewable Energy Hydro, which supplied equipment for the facility.

This means the power-pumped hydropower plant can switch from pumping at full power to running the turbine at full power within five minutes. The volume of water passing through the turbines, 360 cubic meters a second, corresponds to the flow of the Rhone River in Geneva in summer, a spokesperson said.

Pumped storage hydropower plants are important for renewable energy, because wind and solar don’t provide a consistent power supply. These variable-speed turbines supply electricity to the grid quickly, reducing the risk of blackouts.

Nant de Drance has a rated power of 900 megawatts and a storage capacity of 20,000 megawatt hours, which can help facilitate Switzerland’s transition to a renewable energy-powered future. With the addition of Nant de Drance, the installed capacity of pumped hydro storage in Switzerland has jumped 35% to 3,462 MW.

According to an analysis by the International Energy Agency, renewable energy, mostly solar and wind energy, will need to contribute to 90% of the global electricity generation to achieve net-zero emissions by 2050. Solar and wind energy comprised about 71% of the global annual net capacity additions in 2021, said Lin Lu from the Australian National University.

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