The 600-acre cavern will allow Akron-based FirstEnergy Corp. to store energy generated by wind and solar technology for use when customers need it most, the company said.
"The wind doesn't always blow when customers need electricity," said FirstEnergy spokeswoman Ellen Raines.
The utility, which has 4.5 million customers in Northern Ohio, Pennsylvania and New Jersey, has no timetable to begin using the mine, located in the Akron suburb of Norton.
But FirstEnergy says once operational, the commercial-scale compressed-air generating station would be the second in the U.S. and only the third in the world. Other compressed-air generating stations are working in McIntosh, Alabama, and Bremen, Germany, the company said.
Other power companies are investing in the technology.
PSEG Energy Holdings, of New Jersey, is investing about $20 million in similar power storage research and plans to market and license the technology.
During off-peak hours mainly at night, FirstEnergy would generate electricity to run pumps that would fill the cavern with compressed air, Raines aid. The utility would release the air during peak daytime use hours, and it would turn turbines that generate electricity.
Even though there would be a net energy loss from the original electricity used to run the pumps, the system would still benefit the environment because it would cut the need to run power plants during peak use times, and it would store renewable energy, Raines said.
The company would start small with about 268 megawatts of generating capacity, but the mine has the potential to generate 2,700 megawatts, FirstEnergy said.
The purchase price for use of the mine plus 92 acres above it was not disclosed. FirstEnergy's generating subsidiary bought rights to the mine from CAES Development Co. LLC.