Colorado utility Platte River Power Authority has signed an agreement with NextEra Energy Resources to develop a large-scale battery energy storage system, part of a renewable power strategy that includes phasing out its coal-fired power plants.

The utility announced it will build a 100-MW/400-MW-per-hour lithium iron phosphate battery storage system adjacent to its Black Hollow solar project in Severance, Colo., about 60 miles north of Denver. 

The system will be the public utility’s first large-scale battery storage project.

“We are not able to provide details about the pricing or contractor selection status 

Construction began last summer on the 257MW solar project that will be one of the state’s largest such power plants when completed.

Platte River Power Authority and developer Qcells USA Corp. say the project is set to finish next month to serve the communities of Estes Park, Fort Collins, Longmont and Loveland.

Phase two of Black Hollow Solar will add an additional 107MW of capacity in 2026, bringing total capacity to 257MW. When operational, it will increase Platte River’s total solar capacity to 309MW.

The battery plant will connect through a new utility’substation that ties directly into its transmission system.

The projects are part of the utility’s efforts to “actively pursue a 100% noncarbon energy mix,” according to a statement announcing the storage system.

That is part of the statewide move to wind down coal-fired power operations. Platte River plans to retire its jointly owned Craig Unit 1 by the end of 2025, followed by Craig Unit 2 in 2028 and its own Rawhide Unit 1 by the end of 2029. There are four other coal-fired plants in the state, and they are expected to be closed or converted by the end of 2030.

Platte River, based in Fort Collins, supplies wholesale electricity to four municipal utilities that collectively serve more than 150,000 customers across northern Colorado.

Weld Energy Storage, a subsidiary of Juno Beach, Fla.-based NextEra, will own and operate the battery system under a long-term energy storage services agreement. The project is currently in the permitting phase and is expected to break ground in early 2026.