Energy Storage

Concerns about li-ion battery safety in the wake of fires

An Arizona utility regulator is raising questions about the safety of certain lithium-ion batteries, following fires at Arizona Public Service battery storage facilities.

In an Aug 2 letter to her fellow commissioners, commission staff and other interested parties, Commissioner Sandra Kennedy, of the Arizona Corporation Commission, said the types of lithium ion chemistries used at those facilities “are not prudent and create unacceptable risks.”

On April 19, an explosion and fire at APS’ 2 megawatt storage facility at its McMicken substation in Surprise, Arizona injured eight firefighters, four of them seriously.

Kennedy’s letter also cites a November 2012 fire at an APS storage facility at its Elden substation.

That incident had been preceded by a “near miss” in May in which a severely discharged cell in the battery was continuously charged in contravention of design parameters. Kennedy noted there were no subsequent changes to the storage facility’s control system and the event was not disclosed to APS staff by Electrovaya, the designer and installer of the system.

An investigation into the 2012 fire found “inadequate electrical circuit protection and issues with the design of the temperature sensors within the modules,” Kennedy wrote. The investigation warned of “thermal runaway” that can occur when a severely discharged battery cell is charged, resulting in cell deterioration and damage to nearby cells.

The thermal degradation can result in the release of flammable and poisonous gases, including deadly hydrogen fluoride and hydrofluoric acid. The danger is increased because that type of battery fire cannot be suppressed by water but requires a chemical suppressant to suffocate the fire, but use of a chemical suppressant “does not seem viable for a very large facility incident,” Kennedy wrote.

“Knowing now how easily a fire and/or explosion can evidently occur at these types of relatively small (2 MW) lithium ion battery facilities, it appears that a similar fire event at a very large lithium ion battery facility (250+ MW) would have very severe and potentially catastrophic consequences, and that responders would have a very difficult time trying to handle such an incident.” Kennedy wrote.

Kennedy noted that the explosive potential of a 2 MW battery facility is equal to 1.72 tons of TNT and that a 250 MW battery storage facility is equal to 215 tons of TNT. She also noted that the large amount of hydrogen fluoride that could be released could harm the public “at a substantial distance downwind.”

To plan for such a potential catastrophic event, a lithium ion battery storage facility using the same chemistries used at McMicken and Elden would have to be built “in isolation far from everything else,” Kennedy wrote.

APS in February said it plans to add 850 MW of energy storage by 2025 to help integrate a growing amount of renewable resources on its grid.

In an Aug 1 filing of its preliminary Integrated Resource Plan with the Arizona Corporation Commission, APS reaffirmed its commitment to installing 850 MW of energy storage by 2025, but added that the “the timing and sequence of resource additions” will depend on findings regarding the “equipment failure” at the McMicken storage facility.

APS is moving forward with 150 MW of battery energy storage projects being sourced via purchase power agreements selected through a 2018 solicitation, depending on the McMicken findings.The utility did, however, advise bidders participating in its solicitation for 200 MW of energy storage retrofits to stop work on their proposals until further notice.

In addition, with the revised battery project timelines, APS said it would seek short-term wholesale market purchases from neighboring utilities, market participants, and merchant owned natural gas units and demand response projects in order to meet pecking capacity needs for the summers of 2020 and 2021.

APS also said it is developing a request for proposals for up to 50 MW of demand response to be released in the near future.

In an Aug 7 update, APS said the cause of the McMicken fire has not yet been determined and the investigation is ongoing. The utility said the analysis of the factors that led to the failure is expected in September.

While lithium ion batteries hold the overwhelming majority of the utility scale energy storage market, Kennedy suggested that other technologies and chemistries should be looked at in the wake of the APS incidents. She mentioned regenerative zinc air flow batteries, nickel-iron batteries, and magnesium batteries.