August 6, 2020: A lithium battery fire at a 2MW/2MWh Arizona Public Service facility in April 2019 was caused by thermal runaway, a final report by risk management company DNV GL submitted on July 27 concluded.
The fire and explosion, which injured four firefighters and destroyed the utility’s BESS and container, was initiated by an internal cell failure within one battery cell, says the report.
LG Chem, the Korean firm that made the batteries, has rejected the claims.
“It is believed to a reasonable degree of scientific certainty that this failure was caused by an internal cell defect, specifically abnormal lithium metal deposition and dendritic growth within the cell,” says the report, written by Davion Hill, energy storage leader with DNV GL.
It also says that the fire suppression system installed in the BESS was working at first, but was not designed to prevent or stop cascading thermal runaway.
“As a result, thermal runaway cascaded and propagated from cell 7-2 through every cell and module in Rack 15, via heat transfer,” the report says. “This propagation was facilitated by the absence of adequate thermal barrier protections between battery cells, which may have stopped or slowed the propagation of thermal runaway.”
After cascading from module to module, flammable gases were released within the system, and when firefighters opened the door to the BESS after three hours, the gases were ignited and exploded.
The report was commissioned by the Arizona Public Service Company after an explosion at the McMicken Battery Energy Storage Facility, which had been in operation for just over two years.
The battery was made by Korean battery giant LG Chem, and integrated by the energy storage systems provider Fluence. It had been used to integrate solar energy with grid services.
LG Chem, with engineering and scientific consulting firm Exponent, on July 30 sent a 137-page letter plus appendices to the Arizona Corporation Commission refuting the findings, saying the APS analysis did not produce evidence of metallic lithium plating being the cause of thermal runaway, and that their tests did not show internal cell failure.
“Rather, the data collected and analyzed point to initiation of cell thermal runaway through intense heating of the incident cells caused by an external heat source such as external electrical arcing on Rack 15,” the letter says, going on to claim that the DNV GL report ignores evidence to this effect.
“It is our current preliminary opinion that the analysis and testing performed to date does not support a single cell failure initiating the BESS event.”
In South Korea, a string of battery fire incidents, beginning in 2017, resulted in 522 grid installations being dismantled. A report by market intelligence firm S&P Global said investigations into these fires showed the batteries themselves were not the cause of the fires. Instead they were due to poor quality installations, faulty operating procedures, missing protections against electrical shorts and a lack of overall control systems.