A small after 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, hearth department’s Hazmat device, opened the doorway of a container filled with extra than 10,000 energized lithium-ion battery cells, aspect of a utility-scale storage process that experienced been deployed two decades earlier by the community utility, Arizona General public Services.
Before that evening, at all around five:forty one p.m., dispatchers experienced gained a call alerting them to smoke and a “bad smell” in the area all around the McMicken Battery Energy Storage System (BESS) web-site in suburban Phoenix.
Sirens blaring, three hearth engines arrived at the scene within just 10 minutes. Soon after their arrival, very first responders realized that energized batteries were included and elevated the call to a Hazmat reaction. Soon after consulting with utility personnel and selecting on a approach of action, a hearth captain and three firefighters approached the container doorway soon before 8:00 p.m., preparing to open it. The captain, determined in a later investigation as “Captain E193,” opened the doorway and stepped inside. The other three stood nearby.
The BESS was housed in a container organized to maintain 36 vertical racks separated into two rows on either facet of a 3-ft-vast hallway. Twenty-seven racks held fourteen battery modules made by LG Chem, an 80 kW inverter made by Parker, an AES Advancion node controller made use of for info assortment and conversation, and a Battery Security Unit (BPU) made by LG Chem.
The battery modules in turn contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules were linked in series, supplying a per-rack nominal voltage of 721 V. The whole process experienced a nameplate ability to offer 2 MW of ability more than 1 hour for a life time power ranking of 2 MWh. With 27 full racks, there were 10,584 cells in the container. Soon after a full working day of charging, the batteries were all around ninety per cent of ability.
With the doorway to the BESS container open and Captain E193 at its threshold, flamable gases that experienced constructed up inside considering that the incident began many hours before gained a breath of oxygen and uncovered an ignition resource.
The gases erupted in what was described as a “deflagration occasion.” Firefighters just outside of the incident warm zone said they read a loud sounds and observed a “jet of flame” lengthen some 75 ft out and twenty ft up from the doorway.
In the explosion, Captain E193 and firefighter E193 were thrown versus and under a chain-website link fence bordering the facility. The captain landed extra than 70 toes from the open doorway the firefighter landed 30 ft away.
The captain’s injuries involved a traumatic mind harm, an eye harm, backbone injury, damaged ribs, a damaged scapula, thermal and chemical burns, inside bleeding, two damaged ankles, and a damaged foot.
The firefighter endured a traumatic mind harm, a collapsed lung, damaged ribs, a damaged leg, a separated shoulder, laceration of the liver, thermal and chemical burns, a lacking tooth, and facial lacerations.
The timeline and series of activities is not commonly disputed. Having said that, a dispute has erupted in new months more than what precisely transpired inside the BESS container at all around four:fifty four p.m. that initiated a thermal runaway that cascaded across various battery cells.
In a report unveiled in late July, the utility and its third-occasion investigator, DNV-GL, said that their review of the evidence pointed to the failure of a single lithium-ion mobile as triggering the activities.
In a separate, preliminary report submitted times later with state officers, LG Chem, which equipped the li-ion batteries, challenged that acquiring. The South Korea-centered battery supplier said the APS report missed a number of aspects about the incident. People aspects, LG Chem advised regulators, indicated that the mobile thermal runaway began due to “intense heating” brought about by a warmth resource “such as external electrical arcing” on 1 of the battery racks.
Scott Bordenkircher, who served as APS’ Director of Technology Innovation & Integration at the time of the incident, said in an interview that the utility accepts the conclusions of its third-occasion incident investigation, which was concluded by Davion Hill, Ph.D., the U.S. Energy Storage Chief for DNV GL. “We have assurance in our third-occasion investigator,” Bordenkircher said.
In its 78-website page report [PDF], DNV GL said that what was very first believed to be a hearth was in point an substantial cascading thermal runaway occasion within just the BESS. That occasion was initiated by an inside mobile failure within just 1 battery mobile, determined as mobile seven-2 on Rack 15. The failure was brought about by “abnormal lithium metallic deposition and dendritic growth” within just the mobile, the report said.
When the failure happened, thermal runaway cascaded from mobile seven-2 as a result of each other mobile and module in Rack 15 through warmth transfer. The runaway was aided by the “absence of adequate thermal barrier protections” concerning battery cells, which if not might have stopped or slowed the thermal runaway.
As the occasion progressed, a huge amount of money of flammable gasoline was manufactured within just the BESS. Lacking air flow to the outside, the gases made a flammable atmosphere within just the container. All-around three hours after thermal runaway began, when firefighters opened the BESS doorway, flammable gases designed speak to with a warmth resource or spark and exploded.
It was a “tragic incident,” Bordenkircher said.
It also was not the very first time that a lithium-ion battery experienced failed.
The APS report mentioned activities achieving again to 2006 that included thermal runaway activities in lithium-ion batteries. In 1 widely report incident in January 2013, a Boeing 787-8 expert smoke and warmth coming from its lithium-ion battery-centered auxiliary ability device. It was later established that the failure was brought about by an inside mobile defect, which was exacerbated as thermal runaway cascaded as a result of all the cells in the battery pack, releasing flammable electrolyte and gases.
“The point out of the sector is that inside flaws in battery cells is a regarded difficulty,” said Hill. Even so, issues with the technological innovation have not been very well communicated concerning, say, the particular electronics sector and the automotive sector or the aerospace sector and the power sector.
“Overall, across the sector there was a gap in know-how,” Bordenkircher said. The technological innovation moved ahead so swiftly, he said, that benchmarks and know-how sharing experienced not stored up.
The McMicken BESS incident also was not the very first for APS. In November 2012, a hearth wrecked the Scale Energy Storage Technique (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was made by Electrovaya and consisted of a container housing sixteen cupboards made up of 24 lithium-ion cells.
An investigation into that incident established that a severely discharged mobile degraded and affected a neighboring mobile, touching off a hearth. The root trigger of the 2012 incident was uncovered to be defective logic made use of to manage the process.
The manage logic experienced been up-to-date extra than two dozen occasions all through the 11 months that the BESS operated. But many missed options could have prevented the hearth that wrecked the device, the incident report said. It pointed in particular to an occasion the earlier May possibly in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile versus the meant style and design.” Soon after the May possibly occasion, the logic was not modified to handle that poor habits.
An APS spokesperson said that classes uncovered from this 2012 incident were integrated into the style and design and operation of the McMicken BESS.
In its 162-website page rebuttal [PDF] of the McMicken incident LG Chem refuted the utility’s acquiring of fault with its battery.
The battery supplier said that centered on offered evidence, “metallic lithium plating did not trigger an inside mobile failure leading to the preliminary thermal runaway event” at the McMicken BESS facility. As a substitute, mobile thermal runaway began as a result of powerful heating of the affected cells brought about by an external warmth resource, these types of as external electrical arcing on Rack 15.
LG Chem said that its individual third-occasion investigator, Exponent Inc., analyzed the inside mobile failure concept. It did so by forcing a parallel mobile configuration into thermal runaway. It then when compared the ensuing voltage profile to the voltage profile recorded all through the incident. It uncovered that the two did not match, leading to the summary that the explosion’s trigger was unlikely to have been “an inside brief within just a single mobile.”
The battery maker also said that info recorded all through the incident showed a discharging present of four.9A (amps) present all through the voltage excursion. It said that even though the APS report acknowledged that the present flipped from -27.9A charging to four.nine A discharging,“it supplied no rationalization for the occasion.” To LG Chem, nevertheless, the point that the discharging present was at four.9A, alternatively of zero, “means the present without a doubt flowed to someplace else,” supporting what it said was a probably double-stage electrical isolation failure and not an inside mobile brief.
(Complicating the post-incident investigation was the point that the hearth wrecked process manage electronics within just the container. That left dozens of battery modules energized with no way to discharge them. It took seven months for the utility to determine out a approach to remove the modules 1 by 1 and bleed off their saved power.)
The experiences and their divergent conclusions sign the start off of competing interpretations of offered info as the utility and its battery supplier operate to discover a single trigger for the incident.
“We do not want a community argument about it,” said DNV GL’s Davion Hill. For him, the main stage is that “we experienced a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The goal now really should be to make storage devices safer as a result of benchmarks enhancement and information and facts sharing.
Soon after the incident, APS put a maintain on BESS deployment across its services territory. The technological innovation is viewed as critical to meeting the utility’s declared goals to make one hundred per cent “clean energy” by 2050. Two other BESS devices that experienced been working at the time of the April 2019 incident were taken offline they will continue being idle until retrofits can be made and installed.