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canton of Valais.

Six pump turbines send water from the lower reservoir of Emosson to the upper reservoir of Emosson Vieux during times of overproduction.

With a capacity of 25 million m3, the water battery has a power output large enough to power as many as 900,000 homes.

Water batteries have become a popular way to store energy, with figures from the US Office of Energy Efficiency and Renewable Energy revealing that 93 percent of energy storage in the country coming from pumped storage hydropower.