Tucson Electric Power plans to begin construction before the end of the year on an estimated $294-million battery system for solar energy that, at peak efficiency, would store 800 MW hours. The system, sited near its Vail substation in Tucson, Ariz., would have the capacity to power approximately 42,000 homes for four hours, according to TEP.

If completed as scheduled in the summer of 2025, the Roadrunner Reserve Battery Energy Storage System, which will use lithium-iron phosphate battery cells not lithium ion cells, would be the largest battery facility of its kind on the utility’s grid and among the largest in Arizona. TEP, which will own and operate the Roadrunner Reserve BESS, currently has 51 MW of battery storage capacity.

Designed for a 20-year service life, the facility also is "one of the largest projects of its kind in the country," says Johnnie Taul, CEO of DEPCOM Power, Scottsdale, Ariz., which will deliver the project under an engineer-procure-construct contract.

Lithium-iron phosphate battery cells offer longer life at a lower cost compared with lithium-ion batteries, according to the utility. Also, unlike lithium ion batteries, LFP batteries, as they are known, don't contain nickel or cobalt, which are supply-constrained. 

The project complies with the company’s plans to reduce carbon emissions by 80% and add up to 1,400 MW of storage by 2035, according to Joe Barrios, TEP's spokesman.

“Roadrunner Reserve will help us maintain reliability as we ambitiously but responsibly expand our community’s renewable resources,” Susan Gray, TEP’s president and CEO, said in a release. The utility says battery systems help optimize wind and solar resources by shifting their output to periods of greatest need.

TEP plans to charge the grid-connected battery storage system in the morning and early afternoon, when solar power arrays are most productive, then deliver stored energy later in the day when customers’ energy use is typically highest. “This new system will be particularly important in helping us satisfy peak energy needs during the summer,” Gray says.