Across the United States, thousands of abandoned coal mines may soon get a surprising second life as large-scale energy storage systems. 

Researchers at Oak Ridge National Laboratory are studying how these underground spaces could be converted into pumped-storage hydropower facilities, essentially turning old mines into giant “water batteries.” The concept stores electricity by pumping water uphill when power is plentiful and releasing it to generate energy when demand rises. 

Repurposing existing mine infrastructure could lower construction costs and expand long-duration energy storage in regions that lack traditional hydropower geography. If successful, the idea could transform relics of the fossil-fuel era into valuable assets for a cleaner, more resilient power grid.