Swiss 'water battery' boosts Europe's energy storage plans

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.

Balancing role between electricity production and consumption

"When there is too much electricity in the grid, coming for example from solar or wind production, Nant de Drance pumps water from the lower reservoir into the upper reservoir. In doing so, it consumes electricity. Conversely, when electricity demand is higher than production, Nant de Drance turbines the water from the upper reservoir and returns it to the lower one, thus producing electricity," Aline Elzingre-Pittet from the company that operates the power station told DW.

The upper reservoir, like a huge ecological battery, stores energy until it is needed, thus maintaining the balance between production and consumption on the electricity grid.

"Nant de Drance is a net consumer of electricity. Its role is to store energy produced at a time when it is not needed. It does not produce additional electricity," explained Elzingre-Pittet. This means it returns about 80% of the electricity it takes in back to the grid and stores around 20 hours of backup energy.

Open-flow pumped storage hydropower stations built on river systems traditionally require dam construction and disrupt wildlife and damage ecosystems. Andrew Blakers, an engineering professor at the Australian National University, estimates that to power a city with 1 million inhabitants for 24 hours requires around two square kilometers of flooded land.

Nant de Drance, meanwhile, used existing dam and reservoir infrastructure, with most of the work carried out underground, thus limiting its impact on the landscape.

This technology is also ideal for combining with other renewables. For example, two of the reservoirs at the Linth–Limmern Power Stations near Linthal in Switzerland are linked to a nearby solar farm.

Green ownership

The power station is operated by the company Nant de Drance SA, which is owned by four partners: Alpiq (39%), Swiss Railways (SBB) (36%), Industriellen Werke Basel (15%) and Swiss hydroelectricity producer FMV (10%). The share capital of the company is 350 million Swiss francs.

"With the Swiss Federal Railways being part owners, it's not surprising that this kind of storage/production is very useful for powering public transport," Jonas Schmid from environmental group WWF Schweiz told DW.

"SBB currently operates with a 90% share of hydropower, the majority of which is generated by our own power plants. From an environmental perspective, this makes SBB one of Europe's leading railway operators. However, we also rely on domestic electricity from the 50 hertz grid for our buildings, railways stations and technical facilities. This makes Nant de Drance an important and flexible storage space that will help to stabilize the Swiss and European power grids," said Vincent Ducrot, CEO of SBB.

The four partners bear the costs in proportion to their shareholding. In return, they benefit from the power station's production and pumping capacities, also in proportion to their shareholding, and manage the energy according to their needs, said Elzingre-Pittet.

The upfront costs of constructing hydropower facilities are high and Nant de Drance finances itself on debt and equity markets whenever needed, she added.

However, initial expenses pay dividends in the medium and long term. Dams and stations require minimal maintenance and very low operational expenditures compared to other renewable power sources.

"We are also very aware that hydropower development has had enormous effects on freshwater ecosystems and biodiversity throughout Europe due to inundations, fragmentation or hydropeaking [when the water level increases suddenly — Editor's note], which has led to a loss of habitat and disappearance of, for example, migratory fish populations, and a wide array of organizations are working towards restoring those habitats," said WWF's Schmid.

In 2021, Nant de Drance SA, WWF and Pro Natura announced 15 projects to offset the environmental impact of the power plant's construction. The projects were mostly aimed at recreating local biotopes, especially wetlands, to encourage the recolonization of the area by animal and plant species that are endangered in Switzerland.

Hydropower: Future with a past

Limiting the global temperature rise to 1.5 degrees Celsius (2.7 Fahrenheit) will require doubling global hydropower capacity by 2050, according to last year's forecast by International Energy Agency. Hydropower generates 16% of the world's total electricity, the same as wind and solar combined, and around 60% of all renewable electricity.

Pumped storage hydropower could provide energy security outside of Europe, too. Major new projects, like the Wudongde project in southwest China, are cases in point. The 10,200-megawatt project began full operation last year and consists of 12 turbines, each with the capacity to generate 850 megawatts.

Edited by: Ashutosh Pandey