Tesla grid battery fire shows young industry’s failures and successes

The biggest grid battery complex in the U.S. is also the most fire-prone.

The latest fire ignited in the wee hours of Tuesday, September 20 at utility PG&E’s Elkhorn plant in the coastal town of Moss Landing, California. The Tesla-supplied battery plant sits at a utility substation right next door to the Moss Landing battery plant, owned by electric generating company Vistra, which suffered two fires of its own in the last year and had to shut down for months.

Monterey County confirmed that last week’s fire affected only one Tesla Megapack enclosure, and it was contained by the evening of the same day.

Nevertheless, the incident locked down a stretch of California’s iconic Highway 1, and triggered warnings to local residents ​“to keep windows closed and turn off ventilation systems” pending testing for hazardous emissions. Local press covered the economic impacts of the shelter-in-place order, and the Santa Cruz Sentinel editorial board called the incident a ​“stark reminder of new technology risks.”

Crucially, nobody was hurt in the fire. That’s a major improvement compared to the 2019 grid battery fire in Arizona that sent four emergency responders to the hospital. The energy-storage industry learned tough lessons from that and improved key elements of battery-plant design to make subsequent projects safer.

But the Tesla fire shows that even state-of-the-art battery plants are still vulnerable — and it comes just as grid battery construction is about to get turbocharged by the Inflation Reduction Act, which includes a dedicated tax credit for exactly this kind of project.

Here are five lessons from the most recent fire as California, the nation and the world gear up for faster energy-storage deployment than ever before.

1. Moss Landing is a model for the clean grid of the future, but so far it’s not working great

California is in the midst of switching from a fossil-fueled grid to a carbon-free system based on massive amounts of cheap renewable energy. But the state can only shut down its remaining gas-burning plants if it has other sources for on-demand power in the hours after the sun goes down.

Lithium-ion batteries are the current go-to choice for that role, and they’re being installed at a breakneck pace. In early 2021, California had 501 megawatts of battery capacity on the grid. Three months later, in July 2021, it hit 1,000 megawatts. By summer 2022, California wielded more than 3,300 megawatts to keep people’s air conditioners running during a sweltering heat wave.

The battery complex near Moss Landing is the world’s largest set of grid batteries built thus far. Vistra’s portion contains 400 megawatts/1,600 megawatt-hours, while the PG&E facility has 182.5 megawatts/​730 megawatt-hours. Vistra plans to nearly double its capacity by installing another 350 megawatts/1,400 megawatt-hours at its facility, the site of a former gas power plant.

These adjacent plants are nestled at a crucial transmission-grid junction south of the Bay Area, where they can pipe in solar production from inland and discharge it to serve the population center to the north.

But batteries can’t keep the lights on if they’re on fire or are shut down pending an investigation.

Vistra’s Moss Landing plant was out of commission for months after an incident on September 4 of last year. The company concluded that its batteries were actually in fine condition, but a trigger-happy smoke detector went off when it didn’t need to. Then the liquid-cooled heat-suppression system leaked and sprayed water on the battery racks, causing short-circuits and electrical arcing. That in turn triggered more water releases.

That wasn’t the fault of the batteries, but it was the fault of the energy storage plant. While repairs were still keeping that part of the plant offline, a similar issue knocked out the undamaged section of the facility in February of this year. The whole plant came back online in July, in time for the scorching summer season.

Then, just as things were humming along, one of Tesla’s units down the road went up in smoke. So far, there’s not been a lot of time when the battery plants in Moss Landing have all just done their job without incident.

2. The limited damage is a win for the industry’s safety improvements

One particular failure looms large in the storage industry’s safety efforts: the McMicken fire of April 2019, at a battery project that AES built outside Phoenix, Arizona. Explosive gases built up inside the enclosure, until emergency responders opened the door. Then an explosion hurled them across the yard, sending four people to the hospital.

Since then, the storage industry has upped its safety game considerably. Unventilated containers are out, in favor of denser blocks of batteries equipped with ​“deflagration panels” to safely channel dangerous gases up and away. The enclosures are laid out onsite with enough distance between them to prevent fires from spreading unit to unit.

There’s no way to eliminate the risk of battery fires completely. The industry has focused on preventing them as much as possible and limiting the damage when they do happen.

The recent Tesla fire demonstrates the success of the damage-limitation protocols: Nobody got hurt, and the fire did not spread. Practically speaking, all the plant owner needs to do is clean up the burned unit and drop a replacement battery block on-site.

3. Even a limited fire is a bad look for the industry

The fact that nobody got hurt doesn’t erase the disruption for the surrounding community of Moss Landing.

Residents had to deal with a day of lockdown and ominous warnings that toxic air could float their way until authorities gave the all-clear that evening. Local news reported how a nearby RV park lost out on tourist business. Anyone trying to cruise down the Pacific Coast Highway for their daily commute or a transcendental retreat to Big Sur found their way blocked.

Batteries are, generally speaking, better neighbors than fossil-fueled power plants. They don’t routinely emit local pollutants into the air their neighbors breathe, nor do they emit planet-warming gases. They make hardly any noise and have little visual impact on their surroundings. But those benefits could get overlooked if these battery facilities regularly force lockdowns on surrounding communities or threaten to emit noxious gases in the course of a fire and its response.

4. Tesla isn’t invulnerable, but it learns fast

Tesla is a leading provider of battery packs for power plants, on top of its better-known lines of EVs and home batteries. It has a strong reputation for its products, backed by reams of cell-performance data across its many vehicles on the road and its stationary battery packs. For the large-scale Megapack, Tesla early on adopted liquid cooling systems to keep batteries from overheating, back when other companies were still doing that with fans.

All the technological pizzazz hasn’t stopped a couple of fires from bursting out at power plants using the company’s batteries. Prior to the latest blaze at Moss Landing, a Tesla battery pack caught fire during testing at the Victorian Big Battery site in Australia in July 2021. That incident similarly did not injure anyone, and the fire only spread to one adjacent Megapack.

An independent report on that incident noted that the battery ​“failed safely,” and it pinned the root cause on ​“a leak within the liquid cooling system” that led to electrical arcing in the battery’s power electronics. That’s notably not a failure of the battery cells themselves, but of the surrounding systems that turn those cells into a full-fledged power plant.

Tesla’s thermal insulation in the walls of the enclosure prevented the fire from spreading to the next-door unit, just 15 centimeters away. But 20- to 30-knot winds pushed flames to the roof of the neighboring Megapack, where they ignited plastic components that eventually allowed the flames to reach the batteries.

By the time the investigation concluded, Tesla had already designed a new roof shielding to prevent a repeat of this particular form of propagation. It was retrofitting that onto previously installed projects and incorporating it into future designs, alongside software updates to prevent a repeat.

It’s too early to know what caused the latest fire, though something to do with errant moisture would be a logical theory to examine, given recent history.

And Tesla’s Megapack design has already moved on from the generation installed at Elkhorn. That version used nickel manganese cobalt (NMC) chemistry, the energy-dense formula long favored for electric vehicles. Since then, Tesla bloggers spotted signs of the Megapack switching to lithium iron phosphate (LFP) chemistry, known in the industry for its greater resistance to fire.

On an early September visit to the Kapolei Energy Storage plant under construction on the island of Oahu, Hawaii, Canary Media confirmed with developer Plus Power that the new Megapacks going in contained LFP batteries. In other words, Megapacks getting installed today already have new safety features added since the Elkhorn project, which began construction in July 2020.

5. The storage industry is still learning, but it can do that safely

It’s clear from these case studies that the grid battery industry is still young relative to other power plants, and that means failure modes exist that haven’t yet been identified.

While it’s crucial to ensure batteries themselves are manufactured without defects (see GM’s massive and embarrassing Chevy Bolt recall), nonbattery components can cause trouble, too. Tesla’s coolant failure in Australia reads similarly to Vistra’s Moss Landing incidents, where it wasn’t the batteries but the cooling system and the pipes that were the culprits. Presumably, storage installation will include more rigorous stress-testing of plumbing systems going forward.

But even with these unforced errors, it is possible to fail safely. Responders at the Australia fire didn’t blow through a lake’s worth of water trying to quench the insatiable thirst of a roaring battery fire. Instead, they heeded Tesla’s recommended response: Sit back and let the Megapacks burn themselves out while ensuring flames don’t leap anywhere else. Then replace the pack afterward.

Anxious neighbors might not be calmed by assertions of, ​“Don’t worry, we’ll just let the fire run its course.” But that strategy is substantially different from an approach that puts responders in harm’s way, requires obscene amounts of water and potentially incurs hazardous runoff, only to end up with the same outcome.

There’s a long history of fossil gas infrastructure blowing up and killing people. That hasn’t stopped utilities from running gas through major population centers as a matter of course. But nobody alive today remembers the rough-and-tumble early years of gas power adoption. As battery storage matures in real time, its social license depends on its ability to fail without hurting people.