
Page | 001 FINDINGS AND CORRECTIVE ACTIONS SEPT. 4, 2021, INCIDENT MOSS LANDING ENERGY STORAGE FACILITY On the evening of Sept. 4, 2021, the water-based battery heat suppression system activated at the Phase I battery system of the Moss Landing Energy Storage Facility owned and operated by a wholly owned subsidiary of Vistra Corp. The ensuing incident caused damage to roughly 7% of the facility’s battery modules and to other facility systems. There were no injuries or community impacts from the incident. Vistra has prioritized safety as it conducted, in coordination with its outside experts, a five-month long investigation into the incident and developed corrective actions currently being implemented prior to a restart of the facility. Throughout this process, Vistra committed to share its learnings from the incident in order to support the battery storage energy industry and the shared goal of decarbonizing the electric system. The following is a description of the principal findings and corrective actions. 1. Background on Design of the Moss Landing Phase I Battery Heat Suppression System The 300-megawatt facility includes three 100-MW arrays. Each array consists of 32-33 cores, each of which is made up of 47-48 racks containing 22 battery modules. Altogether, the facility has a total of 99,858 modules in 4,539 racks making up 98 cores. The building housing the Phase I battery system has a fire suppression system, including sprinkler pipes. In addition, a separate water-based heat suppression system protects against thermal runaway in individual battery modules. This system includes 25 preaction zones throughout the facility, each of which services 3-4 cores. The preaction zones consist of carbon steel header pipes that are connected by flexible hoses to piping on each rack. The rack piping includes sprinkler nozzles that are inserted into each battery module. The design calls for release of water to the header pipes in a particular zone upon detection of a certain level of smoke by the Very Early Smoke Detection Apparatus (VESDA). After release to the header pipes, water will then be injected into a battery module if the temperature in that module becomes sufficiently elevated to activate the nozzle in that module. Conditions in and around the battery modules are continuously monitored, including the temperatures in each module. 2. Findings Related to the Sept. 4 Incident At approximately 6:41p.m. on Sept. 4, smoke was detected by VESDA units in the vicinity of cores 64, 57, 47 and 41, causing water to be released to preaction zone 24 and stopping the flow of electrical current through the affected cores (an automated process referred to as E-Stop). Due to an apparent programming error in the VESDA, these actions occurred at detected smoke levels below the specified design level at which water was intended to be released and E-Stop was intended to be initiated.
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