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

Earlier that night, at all around five:forty one p.m., dispatchers experienced received a simply call alerting them to smoke and a “bad smell” in the spot all around the McMicken Battery Electricity Storage System (BESS) internet site in suburban Phoenix.

Sirens blaring, three hearth engines arrived at the scene within ten minutes. Shortly soon after their arrival, first responders realized that energized batteries were concerned and elevated the simply call to a Hazmat response. Right after consulting with utility personnel and selecting on a strategy of action, a hearth captain and three firefighters approached the container door soon in advance of 8:00 p.m., preparing to open up it. The captain, recognized in a later on investigation as “Captain E193,” opened the door and stepped inside of. The other three stood close by.

The BESS was housed in a container arranged to keep 36 vertical racks divided into two rows on both aspect of a three-ft-extensive hallway. 20-7 racks held fourteen battery modules created by LG Chem, an eighty kW inverter created by Parker, an AES Advancion node controller utilised for info assortment and interaction, and a Battery Defense Device (BPU) created by LG Chem.

The battery modules in switch contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules were linked in sequence, providing a for every-rack nominal voltage of 721 V. The full system experienced a nameplate ability to source two MW of electricity around a single hour for a life time electrical power rating of two MWh. With 27 complete racks, there were ten,584 cells in the container. Right after a complete working day of charging, the batteries were all around 90 {d11068cee6a5c14bc1230e191cd2ec553067ecb641ed9b4e647acef6cc316fdd} of ability.

With the door to the BESS container open up and Captain E193 at its threshold, flamable gases that experienced created up inside of given that the incident began several hours in advance of received a breath of oxygen and found an ignition source.

The gases erupted in what was described as a “deflagration occasion.” Firefighters just outside of the incident incredibly hot zone stated they read a loud sounds and saw a “jet of flame” lengthen some 75 ft out and twenty ft up from the door.

In the explosion, Captain E193 and firefighter E193 were thrown from and under a chain-hyperlink fence encompassing the facility. The captain landed additional than 70 toes from the open up door the firefighter landed thirty ft away.

The captain’s accidents integrated a traumatic brain harm, an eye harm, spine harm, damaged ribs, a damaged scapula, thermal and chemical burns, inner bleeding, two damaged ankles, and a damaged foot.

The firefighter experienced a traumatic brain harm, a collapsed lung, damaged ribs, a damaged leg, a divided shoulder, laceration of the liver, thermal and chemical burns, a lacking tooth, and facial lacerations.

The timeline and sequence of occasions is not frequently disputed. Having said that, a dispute has erupted in latest weeks around what accurately occurred inside of the BESS container at all around 4:54 p.m. that initiated a thermal runaway that cascaded throughout multiple battery cells.

In a report produced in late July, the utility and its 3rd-get together investigator, DNV-GL, stated that their evaluation of the proof pointed to the failure of a one lithium-ion mobile as triggering the occasions.

In a individual, preliminary report submitted days later on with state officers, LG Chem, which provided the li-ion batteries, challenged that locating. The South Korea-primarily based battery provider stated the APS report skipped a number of aspects about the incident. These aspects, LG Chem advised regulators, indicated that the mobile thermal runaway began because of to “intense heating” caused by a heat source “such as external electrical arcing” on a single of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Engineering Innovation & Integration at the time of the incident, stated in an job interview that the utility accepts the results of its 3rd-get together incident investigation, which was completed by Davion Hill, Ph.D., the U.S. Electricity Storage Leader for DNV GL. “We have self-assurance in our 3rd-get together investigator,” Bordenkircher stated.

In its 78-webpage report [PDF], DNV GL stated that what was first considered to be a hearth was in point an extensive cascading thermal runaway occasion within the BESS. That occasion was initiated by an inner mobile failure within a single battery mobile, recognized as mobile 7-two on Rack fifteen. The failure was caused by “abnormal lithium metal deposition and dendritic growth” within the mobile, the report stated.

When the failure transpired, thermal runaway cascaded from mobile 7-two by means of each other mobile and module in Rack fifteen by using heat transfer. The runaway was aided by the “absence of ample thermal barrier protections” in between battery cells, which in any other case may possibly have stopped or slowed the thermal runaway.

As the occasion progressed, a large volume of flammable gas was produced within the BESS. Missing air flow to the outside, the gases developed a flammable atmosphere within the container. All-around three hours soon after thermal runaway began, when firefighters opened the BESS door, flammable gases designed make contact with with a heat source or spark and exploded.

It was a “tragic incident,” Bordenkircher stated.

It also was not the first time that a lithium-ion battery experienced failed.

The APS report shown occasions achieving back again to 2006 that concerned thermal runaway occasions in lithium-ion batteries. In a single extensively report incident in January 2013, a Boeing 787-8 experienced smoke and heat coming from its lithium-ion battery-primarily based auxiliary electricity device. It was later on established that the failure was caused by an inner mobile defect, which was exacerbated as thermal runaway cascaded by means of all the cells in the battery pack, releasing flammable electrolyte and gases.

“The point out of the market is that inner flaws in battery cells is a regarded situation,” stated Hill. Even so, challenges with the engineering have not been properly communicated in between, say, the own electronics sector and the automotive sector or the aerospace market and the electrical power market.

“Overall, throughout the market there was a hole in know-how,” Bordenkircher stated. The engineering moved forward so immediately, he stated, that benchmarks and know-how sharing experienced not retained up.

The McMicken BESS incident also was not the first for APS. In November 2012, a hearth destroyed the Scale Electricity Storage Procedure (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was created by Electrovaya and consisted of a container housing sixteen cabinets containing 24 lithium-ion cells.

An investigation into that incident established that a severely discharged mobile degraded and influenced a neighboring mobile, touching off a hearth. The root trigger of the 2012 incident was found to be defective logic utilised to handle the system.

The handle logic experienced been current additional than two dozen situations for the duration of the 11 months that the BESS operated. But several skipped chances could have prevented the hearth that destroyed the device, the incident report stated. It pointed in individual to an occasion the past May well in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile from the intended design.” Right after the May well occasion, the logic was not improved to handle that poor actions.

An APS spokesperson stated that lessons uncovered from this 2012 incident were integrated into the design and operation of the McMicken BESS.

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

The battery provider stated that primarily based on available proof, “metallic lithium plating did not trigger an inner mobile failure foremost to the initial thermal runaway event” at the McMicken BESS facility. As an alternative, mobile thermal runaway began by means of extreme heating of the influenced cells caused by an external heat source, these kinds of as external electrical arcing on Rack fifteen.

LG Chem stated that its own 3rd-get together investigator, Exponent Inc., tested the inner mobile failure theory. It did so by forcing a parallel mobile configuration into thermal runaway. It then as opposed the resulting voltage profile to the voltage profile recorded for the duration of the incident. It found that the two did not match, foremost to the summary that the explosion’s trigger was not likely to have been “an inner brief within a one mobile.”

The battery maker also stated that info recorded for the duration of the incident confirmed a discharging recent of 4.9A (amps) existing for the duration of the voltage tour. It stated that even though the APS report acknowledged that the recent flipped from -27.9A charging to 4.9 A discharging,“it provided no rationalization for the occasion.” To LG Chem, on the other hand, the point that the discharging recent was at 4.9A, as an alternative of zero, “means the recent indeed flowed to someplace else,” supporting what it stated was a possible double-issue electrical isolation failure and not an inner mobile brief.

(Complicating the submit-incident investigation was the point that the hearth destroyed system handle electronics within the container. That still left dozens of battery modules energized with no way to discharge them. It took 7 weeks for the utility to figure out a strategy to take away the modules a single by a single and bleed off their saved electrical power.)

The reviews and their divergent conclusions sign the begin of competing interpretations of available info as the utility and its battery provider work to uncover a one trigger for the incident.

“We do not want a general public argument about it,” stated DNV GL’s Davion Hill. For him, the primary issue is that “we experienced a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The objective now need to be to make storage methods safer by means of benchmarks advancement and information sharing.

Right after the incident, APS placed a keep on BESS deployment throughout its service territory. The engineering is seen as vital to meeting the utility’s introduced aims to create 100 {d11068cee6a5c14bc1230e191cd2ec553067ecb641ed9b4e647acef6cc316fdd} “clean energy” by 2050. Two other BESS methods that experienced been running at the time of the April 2019 incident were taken offline they will continue to be idle till retrofits can be built and set up.