After 14 years of work and intensive testing, the Nant de Drance pumped storage power plant in Valais, Switzerland, was placed into operation on 1 July 2022.
The 900MW project is set to play a key role in the stabilisation of the Swiss and European electricity grids, contributing towards the security of supply of electricity in Switzerland. Nant de Drance SA and its stakeholders Alpiq, SFR, IWB and FMV are to officially inaugurate the project in September 2022.
Located 600m below ground in a cavern between the Emosson and Vieux Emosson reservoirs in the Finhaut municipality of Valais, the Nant de Drance power plant features six pump turbines with a capacity of 150MW each. The highly flexible machines make it possible to switch from pumping at full power to turbining at full power in less than five minutes. The volume of water passing through the Nant de Drance turbines, 360m3 a second, corresponds to 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. These characteristics allow Nant de Drance to play a crucial role in stabilising the electric grid.
At the peak of construction, up to 650 workers worked on the construction site and some 60 companies came together to realise this structure in the Alps at a cost of around 2 billion Swiss francs. Situated at the heart of the mountain, the power house cavern measuring 194m long, 52m high and 32m wide required the excavation of 400,000m3 of rock and the drilling of 17 km of tunnels. The Vieux Emosson dam located at 2200m altitude was raised by 21.5m in order to double the capacity of the reservoir and thus provide adequate storage capacity for the facility.
In order to minimise its environmental impact, Nant de Drance worked closely with environmental organisations right from the earliest stages of the project. Fourteen projects at a total cost of twenty-two million Swiss francs have been, are or will soon be completed to offset the environmental impact of the construction of the pumped storage power plant and the very high-voltage line connecting it to the power grid.
Most of the measures aim to recreate specific biotopes locally, especially wetlands, in order to encourage recolonisation of the area by certain rare or endangered animal and plant species in Switzerland.