Switzerland develops underground hydroelectric power

Switzerland has developed an underground hydroelectric power plant that says it has capacity to store enough electricity to charge 400,000 car batteries simultaneously.

The plant, which has taken 14 years to build, will be officially opened next month.

Developers of the 2.2 billion Swiss franc ($2.30 billion) Nant de Drance plant in the canton of Valais, which came online in July, claim the facility operates like a giant battery.

A water battery or pumped storage power plant is a type of hydroelectric energy storage. The battery is made from two large pools of water located at different heights.

It can store excess electricity by pumping water from the lower pool up to the higher pool, effectively “charging” the battery.

When electricity is needed, the direction of the water is reversed. The flow of water rotates a turbine which generates hydroelectric power.

It has six turbines which are tucked into a cavern 600 metres below ground between the Emosson and Vieux Emosson reservoirs.

The turbines have capacity of 900 MW, making it one of the most powerful pumped storage plants in Europe.

During peak demand, Nant de Drance produces electricity from hydroelectric power. However, when output from sources such as wind and solar exceeds demand, the plant stores the surplus electricity by pumping water into the higher Vieux Emosson reservoir. 

It takes less than five minutes to switch from full pumping mode to full power generation. At 360 cubic metres per second, the volume of water passing through its turbines corresponds to the summertime flow of the Rhone river through Geneva.

Typically the plant pumps water into storage in the afternoon, at night and on weekends, then generates power in the morning and evening when prices are higher.

The battery is located 600 metres underground between the reservoirs of Emosson and Vieux Emosson in Valais.

It took 14 years to complete because of considerable logistical and engineering challenges. To create the plant, 18 kilometres of tunnels had to be dug through the Alps.