The Public Service Commission this week voted unanimously to proceed with NorthWestern’s application to purchase energy storage at the battery facility over the next 20 years at an estimated cost of $145 million.

The utility company first announced the project last spring as part of a plan to add 350 megawatts of energy capacity by contracting for storage and hydropower, while also constructing a gas-fired power plant south of Laurel.

The utility plans to charge the 50-megawatt battery facility with power purchased on the open market when prices are low and draw power when prices are high. Pending PSC approval, NorthWestern would contract with storage owner Beartooth Energy Storage LLC. The developer behind Beartooth is esVolta, a Colorado company. The storage facility would be located in Billings.