14 Years In The Making, 20 GWh Pumped Hydro Storage Facility Comes To Switzerland (With Video)

Switzerland is about to bring one of the largest pumped hydro facilities in the world online. 14 years in the making, the Nant de Drance installation has a maximum energy storage capacity of 20 gigawatt-hours. And of course, being a pumped hydro system, it can theoretically store energy for months or even years, something battery storage technology cannot do as easily.

The installation uses gravity. The Emosson reservoir is an artificial lake built high in the Alps near the border with France in 1955 and has a capacity of 25 million cubic meters (about 6.5 trillion gallons). Over the past 14 years, miles of tunnels have been dug into the mountains to connect it to the Vieux Emosson reservoir to the south.

In between is a giant underground cavern tall enough to fit the Eiffel Tower, where 6 of the largest water-driven turbines in the world are waiting for water rushing down from above to make them spin and generate electricity. Between 2012 and 2016, the height of the Vieux Emosson dam was raised by some 20 meters to increase the reservoir’s capacity and thus store more energy, according to a report by Swiss Info.

The theory behind pumped hydro is simple. Fill the upper reservoir and when you need electricity, let the water flow downhill to power turbines. When there is an abundance of electricity, use it to pump water back uphill for use later. “It is an ecological battery that uses the same water over and over. “The output is more than 80% — for every kilowatt-hour of electricity used to pump the water upstream, 0.8 is fed into the grid,” explains Alain Sauthier, chief engineer and director of the Nant de Drance pumped hydro facility. “The electric storage capacity of the reservoir surpasses that of 400,000 electric car batteries.”

“In the future, it will be increasingly necessary to store large amounts of electricity, as renewable sources gradually replace nuclear and fossil energy,” Sauthier says. He adds that solar and wind power are volatile resources that do not necessarily generate electricity when it is needed, which is why systems such as this are so important. They can store energy and help keep the entire European electrical grid stable.

Inside The Nant de Drance Pumped Hydro Facility

Since the project began 14 years ago, 18 kilometers of tunnels have been cut into the Valais Alps between the two reservoirs. Heavy vehicles used those tunnels to bring in all the material and equipment needed to complete the project, from prefabricated buildings with offices to ball valves weighing over 100 tons. The engine room at the heart of the system is 200 meters long, 32 meters wide, and 52 meters high. With a capacity of 900 megawatts, Nant de Drance is one of the most powerful generating plants in Europe.

Sauthier is especially proud of the 6 pump/turbines, which are almost unique in the world in terms of their sheer size and the technology used. “In less than ten minutes, we can reverse the direction of rotation of the turbines and switch from electricity production to storage. Such flexibility is key in order to react promptly to the needs of the electricity grid and adapt electricity generation and consumption. Otherwise, you risk a collapse of the grid and blackout, as happened in Texas at the beginning of the year.”

The plant is vital in order to guarantee electricity supply and grid stability, “but it is far too big for Switzerland,” according to Sauthier. “It can play a role in stabilizing the grid at European level. We are geographically at the heart of the continent and energy flows pass through Switzerland. If there is an overproduction of wind power in Germany, we can use the surplus electricity to pump and store water.”

The Nant de Drance power plant is owned by a consortium led by electricity producer Alpiq and Swiss Federal Railways. Once it is operational, it will need to be profitable to justify the investment needed to make it a reality. This is no easy feat in a sector that has had to contend with financial difficulties and the unpredictability of the electricity market in recent years.

“We are working on the price differential. We need to react quickly and pump when the price is low and (generate electricity) when it is high. In the past, we used the turbines by day and pumped by night, but now the situation has changed, with consumption peaking late in the evening,” Sauthier says.

Nant de Drance will be fully operational for commercial production by summer 2022. Its owners hope it will become profitable once nuclear power plants have finally been shut down and when renewable energy sources have taken over from fossil fuels.

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616,000 Pumped Hydro Sites Worldwide

According to Matthew Stocks of the Australian National University, there are 616,000 sites around the world where closed circuit pumped hydro facilities could be built. Building just 1% of them could solve all problems associated with the storage of intermittent energies based solely on geographical considerations, he says.

In the future, pumped storage power stations will enable the storage of ever greater amounts of green electricity, for release later in times of shortage, writes the Association of Swiss Electricity Companies. “Thanks to its power plants, Switzerland can help balance irregularities in electricity production in Europe. However, we should not overestimate their role, which above all depends directly on the capacities of existing lines,” the association adds.

“Pumped-storage hydro-power is a mature technology,” says Benoît Revaz of the Swiss Federal Office of Energy. More progress is needed however, he believes, to make the system more flexible compared with current operating conditions. Together with 11 other countries, Switzerland is taking part in an international forum aimed at reinvigorating the development of pumped hydro storage in electricity markets.


Bringing the Nant de Drance pumped hydro facility on line this summer couldn’t come at a better time for Europe. The war crimes being perpetrated by Russia on Ukraine have roiled European energy markets as the supply of cheap methane from Russia has been dramatically curtailed.

Switzerland is planning a number of steps to lower the demand for electricity this winter. First the government will request voluntary conservation steps, then it plans to curb non-essential uses like illuminating shop windows, using mobile heaters, or other uses of nighttime lighting. Finally, it could order as many as 30,000 companies to save up to 30% of their electricity usage if necessary. It is estimated those three steps could cut power demand by up to 30%. As a last resort, the government could shut down parts of the electrical grid.

“You have to imagine this as a puzzle. Individual segments would be removed for four hours, then turned back on while others are removed. Some parts of the network — the pieces of the puzzle — would have no power for four hours, then have power again for four or eight hours again depending on the situation,” Michael Frank, director of the VSE association of Swiss electricity companies, tells Reuters.

The Takeaway

Pumped hydro may seem like a magic bullet by many proponents of renewable energy. But at 14 years from start to finish, development times are similar to new nuclear power plants — in other words, way too long. Plus, too, and also, it can’t be built just anywhere, which means high voltage transmission lines need to be constructed to link the renewables with the storage.

But for those situations where it makes economic sense, it’s a brilliant solution to the energy storage problem. There are no lithium, nickel, cobalt, or manganese deposits that have to be mined or processed in order to manufacture batteries. The only active medium is water and so once construction is complete, there are no carbon emissions associated with pumped hydro facilities. Some even suggest all that water in the reservoirs are a perfect opportunity to add floating solar to the picture, which does seem like a match made in heaven for renewable power advocates.


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