Tucson Electric Power Doubles Roadrunner Reserve to 400 MW, Lifting Its Storage Fleet to 550 MW
- Energy Storage News Utility-Scale BESS
Marin Holt
- 0
- 7 minutes read
- Total capacity: 400 MW / 1,600 MWh
- Second phase online: mid-June 2026
- TEP storage fleet: 550 MW
- Phase 1 investment: $350 million
- Homes covered four hours: 85,000 homes
Tucson Electric Power finished the second phase of its Roadrunner Reserve battery in mid-June 2026. The site in southeast Tucson, Arizona now holds 400 MW and 1,600 MWh, double the capacity it carried a year ago. At full charge it covers about 85,000 homes for four hours. DEPCOM Power built both phases under a full engineering, procurement and construction contract.
The expansion moved TEP from a minor storage owner to a large one. The utility held 50 MW of batteries in mid-2025 and holds 550 MW today, a tenfold gain in twelve months.
TEP put about $350 million into the first 200 MW phase, which entered service in July 2025. It has not disclosed the cost of the second. Trade coverage of the expansion repeats that same $350 million figure without stating which phase it covers. Treat any single project total for Roadrunner Reserve with care until TEP publishes one.
Both phases run lithium iron phosphate cells. Roadrunner 2 reaches the same 200 MW and 800 MWh as Roadrunner 1 using 244 battery units against 360. Energy density per enclosure improved between the two builds. TEP charges the batteries in late morning, when solar output runs high and demand runs low, then discharges them through the late afternoon and early evening peak.
The utility credits storage with holding its system together during a peak event on 2025-08-06. Temperatures hit 111 degrees F that day and hourly demand reached 2,502 MW.
The build does not stop here. Wilmot Energy Center II added 100 MW of solar and 100 MW of storage in April 2026. Winchester Solar, near Willcox in Cochise County, is due in early 2027 with 80 MW of solar and 80 MW of storage. TEP spokesperson J.D. Wallace said the utility has more coming after Roadrunner 2, naming Winchester as the next project to reach service.
Why It Matters
A 400 MW four-hour battery reshapes what an Arizona utility does at 6 p.m. Desert peak demand arrives after the sun drops, exactly when solar output falls away, and Roadrunner Reserve moves midday surplus into that window without a new gas plant. The tenfold fleet growth also shows how fast a mid-size utility now adds storage once the first project clears construction.
Watch the disclosure gap instead of the ribbon cutting. TEP published a cost for phase one and stayed quiet on phase two, so ratepayers and regulators lack a per-megawatt trend line across the two builds. That number decides whether the next 200 MW costs less than the last one.
Critical Perspective
The 1,000 percent growth figure is a base effect. TEP held 50 MW of storage a year ago, so almost any utility-scale project produces a headline multiple. The 500 MW added is the real number, and it stands on its own without the percentage.
The cost silence matters more than the ribbon cutting. TEP disclosed about $350 million for phase one and nothing for phase two, built by the same contractor on the same pad to the same rating. That is the cleanest per-megawatt comparison a regulator will ever get, and it is the one TEP did not publish. Arizona ratepayers fund the next tranche without knowing whether the second 200 MW cost less than the first.
Four hours of duration answers a normal evening peak, not the events TEP cites to justify the asset. The 2025-08-06 peak reached 111 degrees F and 2,502 MW. Heat waves of that kind run for days, and a four-hour battery has to recharge fully each midday to show up again the next evening. On consecutive extreme days with high overnight load, that recharge window is exactly what tightens.
DEPCOM built both phases and holds the ongoing operations and maintenance contract, so TEP has concentrated design, construction and long-term service for 400 MW with one vendor. The reliability claim for the 2025 peak event is also TEP describing its own asset. No independent market monitor verified it, because TEP sits outside an organized wholesale market that would produce one.
Sources
- Tucson Electric Power newsroom
- Tucson Electric Power newsroom (phase 1)
- Energy-Storage.news
- KGUN 9 Tucson
- DEPCOM Power project page
