Switzerland is adding a much-needed cog to its energy supply, with the underground power station saying it has the capacity to store enough electricity to charge 400,000 car batteries simultaneously. The $2.3 billion Nantde Drance factory in canton Valais, which opened in July, operates like a giant battery, developers say.

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Its six turbines, hidden in a cave 600 meters underground between the Emosson and Vieux Emosson reservoirs, have a capacity of 900 megawatts, making it one of the most powerful pumped-storage power plants in Europe.

During periods of peak demand, Nantde Drance uses hydroelectric power. But when output from sources such as wind and solar exceeds demand, the plant stores excess electricity by pumping water into the higher Vieux Emosson reservoir. There is a loss like any storage device doing this, but the yield is very good. The efficiency over the entire cycle is about 80%.

The factory took 14 years to build and will officially open next month. It takes less than five minutes to switch from full pumping mode to full generating mode. The volume of water flowing through its turbines at 360 cubic meters per second is equivalent to the flow of the Rhone through Geneva in summer. The amount of energy that can actually be stored in this facility is enormous, around 20 gigawatt hours, which means that 400,000 electric vehicle batteries can be charged simultaneously when the Vieux Fmosson fills the tank. Keywords: engineering news, overseas news

Director Alain Sauthier said the plant typically pumps water into a reservoir in the afternoon, evening and Sunday, and then generates electricity in the morning and evening when prices are higher. This is not only important for Switzerland, but also an important factory at the European level, as it will contribute to the stability of the European energy network and the security of supply in Europe.Editor/XingWentao