Inside Alpiq’s Nant de Drance pumped storage hydropower plant

Le Châtelard, Valais — Nearly every country in the world needs it. Switzerland has it: A way to store energy and add massive flexibility to its energy system. 

Renewable energy generation is on track to surpass coal production for the first time this year, meaning the energy supply is more tied to sun and wind – and less tied to energy demand – than ever before. Energy storage systems like batteries and pumped storage hydropower plants help bridge the gap. And as energy systems become increasingly diverse and decentralized, these storage systems are becoming more valuable than ever.  

While chemical batteries are the cutting edge of innovation, systems that use water account for more than 90% of existing storage capacity. They pump it uphill when there is extra supply and turbinate it down when there is extra demand. 

One such system: Nant de Drance, hidden here in Switzerland inside a mountain at over 2,000 meters above sea level and within walking distance of the French border. 

Capitalizing on the natural advantage created by the Alps and eyeing the enormous value of storage systems, a group led by Swiss utility Alpiq and the country’s national rail SBB invested two billion Swiss francs starting in 2008 to build Nant de Drance. 

megawatts of capacity, comparable to 400,000 electric car batteries

900

of water turbined by the plant in 2023

1.3bn cubic meters

Industrial partner

Now in operation for almost three years, Nant de Drance has 900 megawatts of capacity, comparable to Switzerland’s second-largest nuclear power plant. It can operate for 20 hours under full load, until the plant’s upper reservoir needs to be refilled. 

In total, in 2023, the plant has turbined 1,275.5 million cubic meters of water, which represents fifty times the capacity of the upper reservoir, according to the plant’s mechanical manager Mike Tripodi. This is equivalent to CHF 57.9m in operating income in 2023, the most recent time it published results, all through buying power when the price is low and selling when the price is high. The entire process is without carbon emissions. 

Behind a door into the mountain, at the end of a 5-kilometer-long access tunnel, lies the actual powerhouse of the plant. In a cavern the length of two football fields sit six General Electric pump-turbines that each weigh about 120 tonnes – the same weight as an Airbus A350. They can switch from pumping to turbining water through the plant’s 425-meter vertical shafts within 5 minutes and do so multiple times per day. A remote team working in Lausanne uses market and grid data to decide when to flip the switch. 

“Our power plants operate especially when the sun and wind produce too little or too much, and precisely by doing so, allow renewable energies to be integrated into the system,” Alpiq CEO Antje Kanngiesser said in a recent interview. Her company, an EIP partner since 2019, has become a leader in the flexible energy space. “We continue to invest in storage and flexibility,” Kanngiesser said.

While not every country has the same topographical advantage as Switzerland, if not also the engineering prowess and investment foresight, to build a plant like Nant de Drance, the power plant has an impact far beyond the country’s borders. With its armada of hydropower plants, Switzerland has become something like a battery at the heart of Europe.  

“We are a small country, but we hear from colleagues around the world interested in adding storage to their power grids and to learn about Nant de Drance,” says Nicolas Cherix, operations manager at Nant de Drance “It seems we have something that everyone wants.” 

Alpiq has been an EIP portfolio company since 2019. Read more about the company here.