Moss Landing battery fire hit plant with older, vulnerable technology, expert says

When it opened back in 2020, Vistra Corp.’s Moss Landing battery-powered storage plant was billed as a state-of-the-art component of California’s clean energy future.

Today, that facility – once considered the world’s largest -- is in ruins from a fire last month that burned for two days, destroying 80% of its batteries.

Vistra says it cannot be certain the extent of the damage, however, because its crews have yet to enter the building where the fire occurred. Vistra has two neighboring battery facilities on the Moss Landing site that were not damaged.

The disaster hit just as the state had hopes of quadrupling battery storage beyond the nearly 200 plants already built. The idea behind them is simple: to store the solar energy generated during the day until needed when the sun goes down.

Experts say that in the five years since the Vistra plant opened, energy storage technology has rapidly evolved to avoid such a catastrophe. But the massive fire has local officials challenging the entire concept.

“I mean, nobody in that industry really knows what's happening,” said Monterey County Supervisor Glenn Church, whose district includes the Moss Landing plant. “Nobody in government really knows what to do -- and that is the problem right there.”

Church says he was already dubious of the technology after a fire hit PG&E’s separate system at the Moss Landing plant site back in 2022. He went to officials with Texas-based Vistra Corp. to ask about the larger facility housed inside the Moss Landing natural gas plant.

“I was assured with them saying: ‘You know, what happened with PG&E can’t happen here. We have this great system here,’” Church said.

Vistra officials credited the plant’s cooling system that they told him was designed to prevent overheating of batteries stacked atop each other where plant turbines had once been housed.

“It’s really no longer an emerging technology – it’s here,” says Adam Barowy, a lead researcher with Underwriters Laboratories Fire Safety Research Institute.

He says that while lithium-ion batteries are normally safe, using them on a vast scale poses significant fire safety challenges that the industry is still grappling with.

When those batteries overheat, Barowy says, that can trigger a chemical reaction known as “thermal runaway.” That process doesn’t require oxygen or flames to propagate, he says, and can release flammable gases that can ignite into fire.

“This is not your standard fuel,” he says, and once a fire starts, firefighters have little choice but to simply watch. “There's very limited things the fire service can really do at that scale.”

While Vistra’s stacked battery design relied on a cooling system to guard against thermal runaway, Barowy says that type of indoor, concentrated design is more vulnerable to mass fires, because the batteries are stacked so closely to one another.

The industry has since pivoted to what is considered safer technology: clustering batteries in smaller, compartmentalized outdoor units that resemble cargo containers. The hope is that the outdoor battery packs are spaced far enough apart to avoid catching each other on fire if there is thermal runaway.

But as PG&E learned in 2022, the outdoor battery packs are not fireproof. The utility says a roof leak – caused by faulty installation of rooftop equipment – caused a fire just months after its Elkhorn battery storage facility opened.

While the fire released toxic smoke, prompting a freeway closure and evacuations, only one of the plant’s 256 battery “megapacks” burned. PG&E says the system functioned to limit the spread of the fire. Still, the incident rattled local officials like Church.

But even as the technology has evolved toward more safe design, Barowy acknowledges gaps in the regulations remain. He says he is still confident that the technology will be able to allow the state to safely reach clean energy goals.

“We’ve already seen the technology respond to the new safety regulations—I do believe that's making them safer and I think they'll continue to get safer,” Barowy said.

But Church says the community needs to know now the existing facilities are safe. “We're learning something as we go. And this isn't right.”