By summer 2025, Tucson Electric Power says it plans to turn on a large battery energy storage system in southeast Tucson to store solar energy for use after the sun goes down.
TEP says its proposed Roadrunner Reserve system would be the largest energy storage system on its grid and among the largest in Arizona, with a rated capacity of 200 megawatts and a storage capacity of 800 megawatt hours of energy.
That’s enough to serve up to about 42,000 homes for four hours, the company said.
TEP will own and operate the battery system, which will be designed and built by by Scottsdale-based DEPCOM Power Inc. at a cost of $294 million, the utility said in a filing with the U.S. Securities and Exchange Commission.
The system is at a site adjacent to its existing Vail Substation, off South Rita Road south of Interstate 10.
In June, the Tucson City Council approved a rezoning of the site from rural homestead to industrial classification to accommodate the battery facility, subject to various conditions to comply with building codes, flood regulations, environmental law and aviation regulations.
Construction is expected to begin by the end of the year, TEP spokesman Joe Barrios said.
The new system will use lithium-iron phosphate battery cells, a newer technology TEP says offers longer life and safer operation than other types of battery systems.
A fire at an Arizona Public Service Co. storage battery facility in Surprise in 2019 was blamed on a failure of lithium-ion battery cells using a common nickel-manganese-cobalt-oxide chemistry, which can be prone to runaway failure and fire when overheated or damaged.
TEP says it plans to charge the grid-connected battery in the morning and early afternoon, when solar resources are most productive, then deliver stored energy later in the day when customers’ energy use is typically highest.
“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 news release. “This new system will be particularly important in helping us satisfy peak energy needs during the summer.”
The utility said battery systems help make better use of wind and solar resources by “shifting” their output to periods of greatest need, while helping to smooth out imbalances throughout the day as clouds block the sun or wind patterns change.
TEP currently has 51 MW of energy storage capacity, including its largest system 30 MW battery at the Wilmot Energy Center southeast of Tucson International Airport.
The company said Roadrunner Reserve aligns with its 2020 Integrated Resource Plan, which lays out a plan to reduce carbon emissions 80% and add up to 1,400 MW of energy storage by 2035.
To meet its goals, TEP has put out bid proposals for up to 250 megawatts of new renewable-energy resources like solar and wind farms, along with 300MW of “firm power capacity” such as battery storage.
TEP says it expects to file its next resource plan with the Arizona Corporation Commission on Nov. 1.
DEPCOM Power, a utility-scale solar and energy storage system developer, was founded in 2013 by a group including Jim Lamon, who unsuccessfully ran for the Republican nomination for Arizona senator in 2022.
The company lists a portfolio of more than 4 gigawatts of utility-scale solar and storage projects in more than 30 states, including about a dozen storage installations.
DEPCOM was acquired in 2021 by Koch Engineered Solutions, a unit of Koch Industries, an industrial conglomerate including major oil, gas and chemical operations owned by billionaire conservative activist Charles Koch and other family members.
Tucson Electric Power is bringing its biggest solar and wind projects online as it works toward 70% renewable energy.
