A water battery that can store up to 20 million kWh of electricity constructed in the Swiss canton of Valais is scheduled to start operating on 1 July 2022, announced the company Nant de Drance SA this week.
The Nant de Drance power plant is a pumped storage power plant in a subterranean cavern located between the two reservoirs of Emosson and Vieux Emosson in Valais. The plant took 14 years to build and cost CHF 2 billion.
Located 600 m below ground in a cavern between the Emosson and Vieux Emosson reservoirs in the Finhaut municipality of Valais, the Nant de Drance power plant will feature six pump turbines with a capacity of 150 MW each, a total power output of 900 MW.
The short video below shows the location of the pumped storage power plant.
The plant can be used to store excess electricity by using it to pump water up between reservoirs at different altitudes. The flow of water can then be reversed to produce hydro electricity when it is demanded. This is particularly useful for weather-dependant sources of electricity such as wind and solar. It also complements always-on production such as nuclear, which can produce excesses at off-peak times.
The large hydro battery is set to play a key role in the stabilisation of the Swiss and European electricity grids. It will also contribute towards the security of supply of electricity in Switzerland. On 18 June 2022, Federal Councillor Simonetta Sommaruga and the President of the Cantonal Council of Valais, Roberto Schmidt, inspected the power plant.
The volume of water passing through the Nant de Drance turbines will reach 360 m3 a second, roughly the flow of the Rhône at Geneva in summer. The upper reservoir of Vieux Emosson holds 25 million m3 of water, which represents a storage capacity of 20 million kWh.
At the peak of construction, up to 650 workers worked on the construction site and some 60 companies came together to realise its construction. Situated at the heart of the mountain, the power house cavern measuring 194 m long, 52 m high and 32 m wide required the excavation of 400,000 m3 of rock and the drilling of 17 km of tunnels. The Vieux Emosson dam located at 2,200 m altitude was raised by 21.5 m in order to double the capacity of the reservoir.
The facility is owned by the power companies Alpiq (39%), SFR (36%), IWB (15%) and FMV (10%).
On the occasion of its inauguration, Nant de Drance opens its doors to the general public on Saturday 10 and Sunday 11 September 2022. For security reasons, the number of spaces is limited and registration for the open day events is mandatory. You can register online at this link.