Nant de Drance’s official website states that construction on the project first started in 2008. The business dug a total of more than 10.5 miles of tunnels beneath the Swiss Alps’ Valais mountains during that time. In contrast, the Hoover Dam cost the modern equivalent of roughly $760 million to build, yet it took the 21,000 workers between 1931 and 1936 to develop the well-known American hydroelectric plant. The 14-year construction project cost over $2 billion and required the cooperation of more than 400 people.
The Three Gorges Dam hydropower facility in China, which has a generating capacity of 22,500 MW at any given time, dwarfs the Swiss hydroelectric plant, which has a total capacity of only 900 megawatts. However, Nant de Drance places more value on power storage capability than raw power production. Based on the supply and demand of electricity from other sources, the turbine chamber incorporated within the tunnels connecting Emosson Lake and the Vieux Emosson reservoir facility can swiftly pump water in either way.
These turbines can store more than 20 million kilowatt-hours of water in the Vieux Emosson reservoir, which is carved out of the mountain above Emosson Lake, if there is too much extra electricity coming from the grid. In the event that there is insufficient power to meet demand, water will be forced back through the turbine chambers and into Emosson Lake, powering nearby infrastructure in around five minutes.