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Arizona's largest utility restarts battery build-out after fire

Arizona Public Service will pair its solar plants with a major battery fleet built to rigorous new safety standards.

Julian Spector
Julian Spector
3 min read
Arizona's largest utility restarts battery build-out after fire

Invenergy will build the new batteries for Arizona Public Service in an outdoor cabinet design similar to the ones pictured at Grand Ridge in Illinois. (Photo credit: Invenergy)

Two years after an explosion halted grid battery construction in Arizona, utility Arizona Public Service has resumed building a fleet of batteries to deliver solar power after dark.

The renewed deployment effort carries lessons far beyond the state's borders. The 2019 disaster at APS' McMicken battery plant, which seriously injured four emergency responders, remains the most dangerous energy storage failure in recent U.S. history. But after a year of investigation wrapped up in 2020, APS believes it has crafted a gold-standard battery safety protocol.

"We feel very confident that, as of the technology [available] today, we're building the safest system you can build," Jim Piotrowski, APS' director of distributed energy resources, told Canary Media.

Energy project developer Invenergy will begin storage installation in September at five sites connected to existing solar plants from Phoenix down to Yuma, he said.

  • These projects, totaling 141 megawatts/423 megawatt-hours, should be ready to commission by June 2022.
  • Invenergy will also commence construction on the standalone El Sol battery project, with 50 megawatts/200 megawatt-hours of storage, later this year.

The build-out is also a test case for the role of regulated utilities in creating the clean grid needed to reduce climate-altering carbon emissions.

APS will own and operate the new batch of storage systems, using them to shift solar power into evening hours that would otherwise be served by natural-gas plants. That's critical for the utility's pledge to supply 100-percent-carbon-free power by 2050 — in a state where regulators recently refused to require such a step.

New battery safety features

In early 2019, APS unveiled plans to install 850 megawatts of storage by 2025 to complement existing solar power plants.

When the previously installed McMicken plant started smoking one day in April, a multiproject energy storage contract with Invenergy was "literally ready to sign," Piotrowski said.

The utility froze that contract while it investigated what went wrong at McMicken and how to prevent a repeat. That investigation produced a report in the late summer of 2020, at which point APS worked with Invenergy to craft a new supply agreement.

"We needed to design a system anticipating it will fail," Piotrowski said. "What is not acceptable is to have anybody get hurt."

Instead of putting battery racks in "buildings the size of a football field," Piotrowski said, the companies reimagined the projects to eliminate "occupiable spaces." The batteries will sit in outdoor enclosures at least 100 feet away from any buildings a human could set foot in.

One thing didn't change: Invenergy was always going to buy lithium ferrous phosphate (LFP) battery systems from Powin Energy, the Oregon-based storage integrator. Powin, which champions the safety properties of LFP cells, raised $100 million in February to ramp up grid battery integration work.

Invenergy had favored LFP since "way before it was cool," due to its safety and lack of cobalt, said Derek Price, vice president for renewable engineering. Invenergy now has moved to non-occupiable spaces for the design concepts used in all its storage development. But he stressed that, besides engineering changes, collaboration with first responders is crucial to ensuring improved safety.

"This really focused us on communication, documentation and training on the first-responder level," he said. "There are always ways that you can get better."

Tapping utility cash to decarbonize the grid

Given the lost time, 2025 may be "a little tight" for getting all 850 megawatts of storage up and running as initially envisioned, Piotrowski said.

But the utility is already evaluating bids for 60 megawatts of four-hour storage for sites in the communities of Red Rock and Chino Valley by 2023. More procurement is on the way after that.

"We're moving forward; it's full speed ahead," Piotrowski said. "We're going to make Arizona carbon-free from a utility perspective."

That's well beyond what Arizona law requires. State regulators watered down and ultimately rejected a 100 percent clean energy plan earlier this month.

Some of the battery plants will be owned by developers and contracted to the utility, as in the First Solar battery peaker that beat out gas plant competitors in 2018.

But APS has shown a willingness to own and operate batteries. This approach leverages a traditional strength of utilities — building large grid infrastructure backed by the money flowing from customer power bills — to deploy energy storage, a crucial piece of more renewably powered grids.

A few other utilities have become comfortable with owning large batteries — PG&E owns a portion of its Moss Landing project, and Florida Power & Light is building the massive Manatee project. But for the most part, large battery plants have been led by independent developers mustering their own financing.

“It’s not very often that you see utilities spending hundreds of millions of dollars on this equipment to own it long-term," said Danny Lu, senior vice president at Powin. "This is where the [storage] industry is really going to take off. Once it starts getting rate-based, it’s turning into a super mature industry.”

Energy Storage

Julian Spector

Julian reports on the rise of clean energy. He worked at Greentech Media for nearly five years, and before that he reported for CityLab at The Atlantic.