This $2 Billion Water Battery Could Give Green Energy An Astonishing Backup

Nant de Drance began construction all the way back in 2008, according to the project’s official website. In that time, the company excavated more than roughly 10.5 miles’ worth of tunnels through the Valais mountains in the Swiss Alps. The 14-year construction project cost over $2 billion and required the assistance of more than 400 workers; by comparison, the Hoover Dam cost the modern equivalent of around $760 million to build, though it took 21,000 workers to produce the famous American hydroelectric plant between 1931 and 1936.

At a total capacity of 900 megawatts, the Swiss hydroelectric plant pales in comparison to some of its counterparts, holding little water to the Three Gorges Dam in China, which has a generating capacity of 22,500 MW at any given moment. However, raw power output is less important to Nant de Drance than power storage capacity. The turbine chamber built into the tunnels between the Emosson Lake and the Vieux Emosson reservoir plant is able to quickly push water in either direction based on the supply and demand of electricity from other sources. 

If there’s too much excess electricity coming from the grid, these turbines can store over 20 million kilowatt-hours’ worth of water in the Vieux Emosson reservoir built into the mountain above Emosson Lake by pulling that excess power directly from the grid. Alternatively, if there’s too little electricity to supply demand, water will be pushed back through the turbine chambers and back into Emosson Lake, powering infrastructure in the vicinity within about five minutes.