Safety of Grid Scale Lithium-ion Battery Energy Storage Systems

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– 11 – June 5, 2021
Figure 10: The traditional “fire triangle” does not apply to “thermal runaway”. 3. Thermal Runaway (Battery “fires”)
Li-ion batteries are sensitive to mechanical damage and electrical surges, both in over-charging and discharging. Most of this can however be safeguarded by an appropriate Battery Management System (BMS) and mechanical damage (unless deliberate and malicious) should not be a hazard. Internal cell failures can arise from manufacturing defects or natural changes in electrodes over time; these must be regarded as unavoidable in principle. Subsequent escalation into major incidents can propagate from such apparently trivial initiation.
In July 2020 a thorough failure analysis by Dr Davion Hill of DNV GL [8] was prepared for the Arizona Public Service (APS), following the April 2019 thermal runaway and explosion incident in the 2 MWh Li-ion BESS facility at McMicken, Arizona. This report is revelatory and more detailed than any other failure analysis known to us. It is essential reading for any professional involved in fire safety planning for major BESS. (Figures 11 to 13).
Figure 11: Cells stack into Modules; Modules into Racks; Racks into Strings; Strings into Systems.
Figure12:
Propagation of single Cell failure through Module; cascade to entire Rack.