EPRI Battery Energy Storage Systems (BESS) Failure Incident Database

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Cell failures usually begin with short circuits within the cell leading to eventual thermal runaway. They can originate from poor cell design, manufacturing defects, incorrect installation, or cell abuse.
• Controls
A failure in the sensing, logic circuits, and communica- tion systems. Control systems coordinate the operation of the ESS, including the battery management system (BMS), energy management system (EMS), plant con- trollers, and any subsystems. Controls failures include those due to control system incompatibility, incorrect installation of the control system, defects leading to er- rors in sensors or controls, or inappropriate operation limits.
• Balance of System (BOS)
A failure in any of the elements of a BESS excluding the cells, modules, and controls. BOS typically comprises of, but is not limited to: busbars, cabling, enclosures, power conversion systems, transformers, fire suppres- sion systems, HVAC, or liquid cooling systems.
An incident may have multiple failure elements or root causes; such incidents are assigned multiple classifica- tions. The following example illustrates this classification methodology. The Elkhorn battery facility located at Moss Landing, CA, experienced a fire on September 20, 2022. The investigation report7 was shared publicly by Tesla (the BESS manufacturer and integrator) and Pacific Gas & Electric (site owner). The investigation found that rainwater intrusion
through the container caused electrical arcing within the system, leading to thermal runaway within one BESS unit on site. A water ingress point in the enclosure had been created when an umbrella valve had been dislodged during the improper installation of a vent shield. As a confounding factor, insulation loss alarms were not properly escalated to the operator. Two days after the initial insulation alarms were recorded, smoke and fire were reported to the fire department. Appropriate reporting of the insulation loss alarms could have prevented escalation of the initial failure into a fire that consumed the whole BESS unit. Therefore, the root cause was classified as both an integration, assem- bly & construction failure in the BOS and a design failure of the control system.
RESULTS
Results Overview
The following section contains insights from the 26 in- cidents that were classified. The distributions along the biaxial classification system are examined in detail. As described above, investigations into battery failures are often inconclusive, and there is a lack of transparency that further limits the sharing of lessons learned. The industry experts who provided additional information beyond public reports are based in the United States, so information on incidents in other parts of the world is more limited in this report.
7 Report: Elkhorn Battery Energy Storage System Fire of September 20, 2022 - PGE Currents. https://www.pgecurrents.com/articles/3833-re- port-elkhorn-battery-energy-storage-system-fire-september-20-2022.
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May 2024