Subterranean pumped hydro station boosts Swiss energy supply

After 14 years of construction, the Nant de Drance underground pumped hydropower station has begun to supply electricity to grids in Switzerland and neighboring European countries. With a power capacity of 900 MW, the power plant – commissioned on 1 July 2022 – is one of the most powerful pumped hydro storage plants in Europe and will make an important contribution to Switzerland’s security of supply, according to energy utility Alpiq, the main operator of the facility.

Switzerland’s mountainous geography makes it especially suitable for operating pumped hydro power stations that are connected to Alpine reservoir lakes at high altitudes. This energy storage technology has become even more important in the wake of the Fukushima Daiichi nuclear disaster in 2011, which prompted the Swiss government to ban the construction of new nuclear plants, though legacy installations will be allowed to continue operating for as long as they are deemed safe.?

With pumped power storage, excess energy from stochastic renewable sources like solar and wind power is used to pump water from the lower to the higher reservoir, which has a dam wall that is 205 meters long and 76,5 meters high. When full, Nant de Drance offers up to 20 million kWh of storage capacity, enough to power 400.000 electric vehicle batteries. During periods of high energy demand and low supply, the stored water is released to run through an array of turbines and fed into the grid.

Nant de Drance is situated on the border with France near Mont Blanc, Europe’s highest peak. The installation was built between the reservoir lakes of Emosson and Vieux Emosson, with the powerhouse located 600 meters underground. The facility took 14 years to construct and includes six Francis turbines with a nominal output of 150 MW each for a total power capacity of 900 MW. Its twin vertical shafts are 425 meters deep and seven meters wide, and the plant includes 17 kilometers of subterranean tunnels.

The plant gives the grid operator a high degree of flexibility in grid management and fosters the large-scale uptake of green energy while enhancing grid stabilization. With a conversion factor of over 80 percent, it is one of the most efficient pumped hydropower station currently in operation. The pumped storage facility is operated by Nant de Drance SA, whose shareholders include Alpiq (39 percent), Swiss rail operator SBB (36 percent), and two regional utilities serving the regions of Basel (IWB, 15 percent) and Valais (FMV, 10 percent).

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AUTHOR

Chris Findlay, Supertrends