PG&E Shares Findings of September 2022 Moss Landing Megapack Incident

CASTROVILLE — Representatives PG&E presented at a Monterey County Town Hall meeting today where they updated community stakeholders with information related to PG&E’s 182.5-megawatt (MW) / 730-megawatt hour (MWh) Elkhorn battery energy storage system at its Moss Landing electric substation. 

During the meeting, Teresa Alvarado (vice president, South Bay & Central Coast Region, PG&E), Dave Gabbard (vice president, Pacific Generation, a subsidiary of PG&E), and Sam Garcia (acting director, Environmental Management, PG&E), presented findings from an independent investigation of the Sept. 20, 2022 fire incident, shared insights from a newly developed plume dispersion model, and outlined the corrective actions and mitigations that PG&E has taken since the incident. 

PG&E restarted Elkhorn battery system operations on December 30, 2022, after Energy Safety Response Group (ESRG) — an independent energy safety consulting firm — completed its investigation of the September 2022 fire incident, and after PG&E and Tesla implemented corrective actions and conducted extensive system testing.

“At PG&E, we are committed to making our system safer every day — across every part of our operations, and when designing the Elkhorn Battery, our team coordinated closely with Tesla and the North County Fire Protection District to create a comprehensive set of emergency safety plans including steps to ensure proper emergency preparation, detection, situational awareness and response,” Gabbard said. “The results of the investigation and the corrective actions we’ve implemented will help prevent incident reoccurrence and can serve as a resource for our sister utilities, stakeholders, and industry partners.”

Investigation findings, root cause analysis and corrective actions implemented

ESRG conducted and completed a root cause analysis investigation of the Fall 2022 incident, revealing that an equipment installation issue resulting in water ingress caused the battery’s cells to overheat and catch fire. 

Specifically, an improperly installed vent shield dislodged an umbrella valve on the top of the Megapack, causing an unnatural water ingress point, ultimately resulting in battery cell overheating and thermal runaway. 

The investigation identified that 88 Megapacks in total experienced water intrusion as a result of improperly installed vent shields. All 88 were inspected, damaged parts replaced and re-tested.

PG&E and Tesla have implemented several corrective actions to reduce the potential for a similar incident occurring in the future, primarily by addressing the improperly installed equipment, improving monitoring processes, and implementing additional automated features. A summary of the investigation findings and corrective actions can be found in the pdf document below.

Incident background and system safety

During the September 2022 incident, one Tesla Megapack out of 256 on site caught fire and the safety systems at the facility worked as designed and automatically disconnected the battery storage facility from the electrical grid.

PG&E immediately worked with firefighters to provide a safe area for emergency response personnel. The incident was managed consistent with the firefighting strategy outlined in the pre-fire plan (a training program and Emergency Action Plan involving both PG&E and the North County Fire District) where responders employed a defensive firefighting strategy that allowed the one Megapack to burn itself out and prevented fire damage to adjacent Megapacks.

The Elkhorn Battery system is engineered to mitigate thermal events through a series of safeguards, including Megapack fire certification, telemetry-triggered warning alarms that provide monitoring, early detection, and automated de-energization if flames are detected.

These alarms alert the Tesla Remote Monitoring team, PG&E’s Fresno Operations Center and are audibly and visually communicated across the site.

The Tesla Megapack received an industry-accepted fire safety certification and has undergone safety testing with a nationally recognized lab. 

There were no injuries to onsite personnel and no electrical outages for customers due to the incident.

Immediately following the incident, PG&E and Tesla took several actions to ensure the safety of the system and the community, including: 

• Air sampling (coordinated by the Monterey County Environmental Health Division and conducted by the Environmental Protection Agency and PG&E) indicated there was no threat to human health or the surrounding environment as a result of the fire.

• Worked with County Environmental Health and Tesla environmental teams to restore the site while preserving the local environment. Specifically:

• Collected the water deployed for fire mitigation into tanks, sampled the water and appropriately disposed of it under County oversight.  

• Conducted soil sampling in the vicinity of the impacted battery and removed impacted soils for proper disposal. 

• Importantly, subsequent testing indicated that water and airborne samples from this event showed minimal environmental impact.

• Removed damaged Megapack from the site, performed an extent of condition and inspected all other Megapacks.

• Since the September 2022 incident, PG&E has been in regular communication with state regulators and local officials and has briefed them on the investigation findings and corrective actions.

Plume dispersion modeling

In addition to the corrective actions PG&E has implemented to prevent a potential re-occurrence of a thermal runaway event at the site, PG&E has also taken actions to better inform local residents, businesses, local agencies and law enforcement on the air quality and safety impacts of a potential future incident.

In particular, PG&E commissioned the development of a “smoke plume dispersion model” which summarizes air and smoke dispersion modeling and associated impacts of a future potential battery fire at the Elkhorn facility. 

• The modeling involves several assumptions and inputs including three years of meteorological data and emissions estimates from Tesla’s third-party laboratory battery tests, to predict potential air quality impacts in the area surrounding Elkhorn. This information provides local officials and first responders with guidance around the need for any shelter-in-place orders or road closures as a result of a potential future incident. 

PG&E has also developed a customer outreach plan that outlines steps PG&E would take to inform the local community — in coordination with an Incident Command team that would be immediately established — in the event of a potential future battery fire at the site.

Read the report