Why we don’t need to worry too much about the latest grid battery fire

The fire that ripped through what was once the world’s largest standalone grid battery on January 16 left clean energy fans and foes alike wondering how it happened and what’s preventing another disaster.

Energy company Vistra built the Moss Landing energy storage facility, on the California coast south of Silicon Valley, as a shining example of the clean grid of the future. The facility stored solar power by day and delivered it in the pivotal evening hours when California’s households need the most energy — an emissions-free alternative to burning fossil gas for energy.

The mid-January fire all but eradicated a building that housed 300 megawatts of battery capacity. Investigators are just beginning to sift through the smoldering remains to ascertain the cause of the fire.

On Wednesday, three state legislators representing the coastal area affected by the fire asked the state’s utility regulators ​“for a fully transparent and independent investigation, updated safety enforcement, prevention enhancements, and for the Vistra BESS to remain offline until safety is guaranteed.”

In the meantime, concerned residents staring down battery plants in other parts of the country can take some solace in the fact that Vistra’s Moss Landing facility was one of a kind, conceived and designed before modern safety standards were adopted for large grid batteries. Battery safety standards have been updated multiple times since it was built.

It may sound counterintuitive to think of a storage plant completed in 2020 as outdated. But the grid battery industry has evolved at a rapid pace since then — it’s now the second-biggest source of new U.S. grid capacity, behind solar power.

In that short time, the storage industry has matured through a process of trial and error that has included several high-profile fires. None of these have killed anyone, but a pivotal battery explosion in Arizona in 2019 injured four emergency responders and forced a major reappraisal of grid storage plant design. The industry has also improved the batteries themselves since then, but those upgrades came after construction of Vistra’s landmark battery behemoth.

Moss Landing’s design was ​“unique, globally, as a facility,” given its vintage and the qualities of the 1950s-era building-turned-battery-vault, battery fire safety expert Nick Warner told Canary Media.

In this case, the lack of exact copycats is very good news: It means that the design elements that allowed Moss Landing to burn so apocalyptically are not present in newer or forthcoming battery plants. The bad news is that a handful of other battery projects built around the same time as Moss Landing are slated to operate for years to come.

Key factors in the Moss Landing battery fire

We don’t know what caused the Moss Landing fire, but we do know two big factors that help explain why the facility burned so spectacularly.

First off, Vistra used batteries manufactured by Korea’s LG (not Tesla batteries, as some news reports incorrectly claimed; a separate Tesla battery array sits next door). The LG batteries used the nickel-manganese-cobalt (NMC) chemistry, developed for electric vehicles because it packs a lot of power. That energy density can turn into a vulnerability; when defects cause these batteries to heat up, they can enter thermal runaway, a chain reaction that can quickly run out of control.

Indeed, many of the most prominent battery fires in the U.S. sprang from LG batteries in facilities built around a similar time: the Arizona 2019 explosion, the Gateway project fire of 2024, and now Moss Landing. General Motors also ripped out LG batteries in its $2 billion Chevrolet Bolt battery recall, and LG itself recalled some of its residential battery products in late 2020.

NMC was the dominant chemistry for grid storage in the industry’s early days, as a sort of hand-me-down from the much bigger EV industry. Battery manufacturers have improved their technology and added safety features in the years since Moss Landing was installed.

The grid storage market has also moved away from NMC in favor of lithium iron phosphate (LFP), a chemistry with better safety metrics. Major grid battery supplier Tesla, for instance, switched to LFP for its popular Megapack enclosures in 2021.

The other defining factor specific to Moss Landing was the choice to use a large, legacy building to house rows and rows of battery racks.

That decision made sense at the time. California was looking for big batteries to help its shift to clean energy, and Vistra had taken over the old Moss Landing power plant in its acquisition of power producer Dynegy. In hindsight, it seems that the design choice packed too much battery fuel into one enclosed space, creating the conditions for an unstoppable, 100-foot tower of flames.

Nearly all grid batteries installed in the past several years have opted not for one overarching building but for row upon row of modular battery containers. Each box contains batteries, controls, and safety equipment. Projects are designed so that if a fire breaks out at one individual container, it won’t propagate to neighboring units. This limits the amount of fuel a fire could engulf and makes it easier for emergency responders to suppress a fire with water.

Case in point: A fire broke out at the neighboring Tesla project in September 2022, but it never spread beyond one container, and responders quickly put it out.

A brief history of battery safety regulations

While industry trends have moved toward safer batteries and containerized systems, fire safety codes have also evolved.

Two major fire safety codes govern grid battery installations today: Most states, including California, subscribe to International Fire Code (IFC) guidance on large battery installations, while the remainder adhere to the National Fire Protection Association’s standard, NFPA 855. Committees of battery experts update these codes on a three-year cycle with the best new information (and a public comment process). But those cycles kicked off only recently.

IFC first added a section on large battery storage projects in 2018. NFPA 855 came out in late 2019 for the 2020 calendar year. But it takes a couple of years for states to adopt new fire codes, Warner noted. (He serves as a principal member of the NFPA 855 committee but spoke to Canary Media in his personal capacity.) Some states even fall several cycles behind, then jump to adopting the most recent code. That has left some municipalities to figure out which battery standards to impose on developers, in the absence of a state code that says anything about battery plants.

California regulators formally approved the utility contract for Moss Landing in November 2018. Vistra started construction shortly after and brought the project into operation in December 2020.

The state began enforcing the 2018 IFC update around the time construction at Moss Landing was wrapping up, so the project was grandfathered in for permitting purposes, Warner noted. Vistra brought in consultants and experts to muster the best safety practices in the industry, in lieu of an active battery fire code. The company also incorporated what it knew of the draft language being finalized in the forthcoming codes.

Moss Landing may have reflected the storage industry’s best insights into battery safety, but the industry was considerably younger then. The U.S. installed just 311 MW of storage in 2018, research firm Wood Mackenzie calculated at the time. Two years later, the first tranche of Moss Landing batteries single-handedly delivered 300 MW.

When Moss Landing was under development, the storage industry hadn’t had the opportunity to learn from mistakes. After the battery fire erupted near Phoenix in 2019, an investigation revealed that the fire suppression techniques that had been expected to handle lithium battery fires were insufficient. Another big takeaway was that explosive gases can build up when batteries combust in a closed environment, necessitating ventilation. But that report came out in July 2020, just a few months before Moss Landing got up and running.

The upshot here is that nobody building a battery project today would do it with the particular technological generation of batteries or the fire code specs that Vistra used at Moss Landing. Now the lessons learned from Moss Landing will shape the fire codes for projects that come after.

“I think more likely we will see changes in how many batteries are allowed in a space cordoned by fire walls,” Warner said. ​“We’ll see walls required to run floor-to-ceiling, we’ll see sprinklers implemented differently. … We’ll see additional barriers, like fire curtains, used to separate batteries even within a fire space.”

In another promising new trend for battery safety, leading manufacturers now perform more intensive fire testing of lithium-ion cabinets, not just individual cells or modules, said Warner, who co-founded the Energy Safety Response Group. This kind of large-scale testing with real fire is being incorporated into forthcoming safety code updates, Warner added, and provides much more realistic data for understanding how batteries behave in a fire compared with extrapolations from small-scale fire or stress tests.

The industry’s incremental progress on safety didn’t stop the residents of Moss Landing from having to flee their homes again, and that’s a major failure. But a justifiably wary public can rest assured that this particular facility has little in common with the rest of the United States’ rapidly growing grid battery fleet.