Dispute Erupts Over What Sparked an Explosive Li-ion Energy Storage Accident

Previously that evening, at all around 5:forty one p.m., dispatchers had received a get in touch with alerting them to smoke and a “bad smell” in the area all around the McMicken Battery Energy Storage System (BESS) site in suburban Phoenix.

Sirens blaring, a few hearth engines arrived at the scene inside of 10 minutes. Shortly immediately after their arrival, initial responders realized that energized batteries ended up associated and elevated the get in touch with to a Hazmat response. Right after consulting with utility personnel and selecting on a approach of motion, a hearth captain and a few firefighters approached the container door shortly prior to eight:00 p.m., preparing to open it. The captain, discovered in a later on investigation as “Captain E193,” opened the door and stepped inside. The other a few stood close by.

The BESS was housed in a container arranged to maintain 36 vertical racks separated into two rows on either facet of a 3-ft-vast hallway. Twenty-seven racks held 14 battery modules produced by LG Chem, an 80 kW inverter produced by Parker, an AES Advancion node controller applied for info collection and conversation, and a Battery Security Unit (BPU) produced by LG Chem.

The battery modules in transform contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules ended up related in series, supplying a for each-rack nominal voltage of 721 V. The complete process had a nameplate capacity to source two MW of power in excess of a single hour for a life time power ranking of two MWh. With 27 comprehensive racks, there ended up 10,584 cells in the container. Right after a comprehensive working day of charging, the batteries ended up all around 90 p.c of capacity.

With the door to the BESS container open and Captain E193 at its threshold, combustible gases that had crafted up inside given that the incident commenced numerous several hours prior to received a breath of oxygen and found an ignition source.

The gases erupted in what was described as a “deflagration celebration.” Firefighters just outside of the incident incredibly hot zone said they listened to a loud noise and observed a “jet of flame” extend some seventy five ft out and 20 ft up from the door.

In the explosion, Captain E193 and firefighter E193 ended up thrown towards and below a chain-backlink fence surrounding the facility. The captain landed more than 70 feet from the open door the firefighter landed 30 ft away.

The captain’s injuries involved a traumatic mind damage, an eye damage, backbone hurt, damaged ribs, a damaged scapula, thermal and chemical burns, interior bleeding, two damaged ankles, and a damaged foot.

The firefighter endured a traumatic mind damage, 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 typically disputed. Even so, a dispute has erupted in the latest weeks in excess of what particularly occurred inside the BESS container at all around four:54 p.m. that initiated a thermal runaway that cascaded across a number of battery cells.

In a report released in late July, the utility and its 3rd-party investigator, DNV-GL, said that their overview of the evidence pointed to the failure of a one lithium-ion cell as triggering the activities.

In a individual, preliminary report submitted days later on with state officials, LG Chem, which provided the li-ion batteries, challenged that getting. The South Korea-centered battery provider said the APS report skipped a quantity of aspects about the accident. Individuals aspects, LG Chem instructed regulators, indicated that the cell thermal runaway commenced due to “intense heating” brought on by a warmth source “such as exterior electrical arcing” on a single of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technological innovation Innovation & Integration at the time of the accident, said in an interview that the utility accepts the findings of its 3rd-party accident investigation, which was completed by Davion Hill, Ph.D., the U.S. Energy Storage Leader for DNV GL. “We have self esteem in our 3rd-party investigator,” Bordenkircher said.

In its 78-webpage report [PDF], DNV GL said that what was initial imagined to be a hearth was in simple fact an substantial cascading thermal runaway celebration inside of the BESS. That celebration was initiated by an interior cell failure inside of a single battery cell, discovered as cell 7-two on Rack 15. The failure was brought on by “abnormal lithium metallic deposition and dendritic growth” inside of the cell, the report said.

As soon as the failure occurred, thermal runaway cascaded from cell 7-two through each other cell and module in Rack 15 by using warmth transfer. The runaway was aided by the “absence of enough thermal barrier protections” concerning battery cells, which in any other case could have stopped or slowed the thermal runaway.

As the celebration progressed, a significant volume of flammable gas was produced inside of the BESS. Missing air flow to the outside, the gases produced a flammable atmosphere inside of the container. All around a few several hours immediately after thermal runaway commenced, when firefighters opened the BESS door, flammable gases made make contact with with a warmth source or spark and exploded.

It was a “tragic incident,” Bordenkircher said.

It also was not the initial time that a lithium-ion battery had failed.

The APS report listed activities reaching back again to 2006 that associated thermal runaway activities in lithium-ion batteries. In a single extensively report incident in January 2013, a Boeing 787-eight expert smoke and warmth coming from its lithium-ion battery-centered auxiliary power unit. It was later on identified that the failure was brought on by an interior cell defect, which was exacerbated as thermal runaway cascaded through all the cells in the battery pack, releasing flammable electrolyte and gases.

“The state of the field is that interior problems in battery cells is a identified challenge,” said Hill. Even so, challenges with the technology have not been well communicated concerning, say, the own electronics sector and the automotive sector or the aerospace field and the power field.

“Overall, across the field there was a gap in know-how,” Bordenkircher said. The technology moved forward so rapidly, he said, that benchmarks and know-how sharing had not saved up.

The McMicken BESS accident also was not the initial for APS. In November 2012, a hearth destroyed the Scale Energy Storage Method (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was produced by Electrovaya and consisted of a container housing 16 cabinets that contains 24 lithium-ion cells.

An investigation into that accident identified that a severely discharged cell degraded and impacted a neighboring cell, touching off a hearth. The root lead to of the 2012 accident was found to be defective logic applied to regulate the process.

The regulate logic had been up-to-date more than two dozen situations throughout the 11 months that the BESS operated. But numerous skipped prospects could have prevented the hearth that destroyed the unit, the accident report said. It pointed in specific to an celebration the preceding May perhaps in which a cell was “severely discharged” even as the logic was “continuously charging the cell towards the intended design.” Right after the May perhaps celebration, the logic was not adjusted to handle that inappropriate behavior.

An APS spokesperson said that classes uncovered from this 2012 incident ended up incorporated into the design and operation of the McMicken BESS.

In its 162-webpage rebuttal [PDF] of the McMicken accident LG Chem refuted the utility’s getting of fault with its battery.

The battery provider said that centered on accessible evidence, “metallic lithium plating did not lead to an interior cell failure major to the initial thermal runaway event” at the McMicken BESS facility. As an alternative, cell thermal runaway commenced through powerful heating of the impacted cells brought on by an exterior warmth source, this sort of as exterior electrical arcing on Rack 15.

LG Chem said that its have 3rd-party investigator, Exponent Inc., analyzed the interior cell failure concept. It did so by forcing a parallel cell configuration into thermal runaway. It then as opposed the ensuing voltage profile to the voltage profile recorded throughout the incident. It found that the two did not match, major to the conclusion that the explosion’s lead to was not likely to have been “an interior limited inside of a one cell.”

The battery maker also said that info recorded throughout the incident confirmed a discharging present of four.9A (amps) present throughout the voltage tour. It said that though the APS report acknowledged that the present flipped from -27.9A charging to four.nine A discharging,“it provided no rationalization for the celebration.” To LG Chem, however, the simple fact that the discharging present was at four.9A, as a substitute of zero, “means the present in fact flowed to someplace else,” supporting what it said was a probable double-level electrical isolation failure and not an interior cell limited.

(Complicating the article-accident investigation was the simple fact that the hearth destroyed process regulate electronics inside of the container. That left dozens of battery modules energized with no way to discharge them. It took seven weeks for the utility to figure out a approach to remove the modules a single by a single and bleed off their stored power.)

The experiences and their divergent conclusions signal the start out of competing interpretations of accessible info as the utility and its battery provider work to uncover a one lead to for the accident.

“We don’t want a general public argument about it,” said DNV GL’s Davion Hill. For him, the major level is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The goal now should be to make storage programs safer through benchmarks growth and data sharing.

Right after the accident, APS placed a maintain on BESS deployment across its services territory. The technology is seen as crucial to meeting the utility’s declared plans to develop one hundred p.c “clean energy” by 2050. Two other BESS programs that had been functioning at the time of the April 2019 accident ended up taken offline they will continue being idle until eventually retrofits can be designed and installed.