Vistra Corp announced on September 7, 2021, that it has begun a preliminary assessment of the Phase 1 300 MW/1,200 MWh lithium-ion battery storage system at its Moss Landing Energy Storage Facility in Monterey Bay, California, following an overheating issue on September 4, 2021.[1] Vistra's 300 MW storage system is the largest battery storage facility in the world and began operations in December 2020. Phase II of the project, which added an additional 100 MW/400 MWh, came online in August 2021. Moss Landing operates under a long-term agreement with Pacific Gas & Electric.

According to the statement, "a limited number of battery modules" at the facility overheated, resulting in the facility going offline. Experts from Vistra, engineering contractor Fluence, battery manufacturer LG Energy Solution, and others are conducting the initial investigation into the cause of the issue. The North County Fire Protection District of Monterey County is also helping with the investigation. In a statement, the California Public Utilities Commission said that it is also investigating the incident.[2] The 300 MW unit will remain offline for the duration of the investigation. Vistra's Phase II system, located in a separate standalone building, was unaffected by the incident and remains operational.

[1] https://investor.vistracorp.com/news?item=197

[2] https://investor.vistracorp.com/2021-01-06-Vistra-Brings-Worlds-Largest-Utility-Scale-Battery-Energy-Storage-System-Online