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Vistra battery storage facility in California remains shut after overheating

08 September 2021 George Lobsenz

Vistra Energy's 300-MW Moss Landing lithium-ion battery facility in California remains offline while the company investigates why several modules overheated enough 4 September to trigger sprinkler systems, preventing a fire and any offsite impacts.

The company said 7 September the facility might be out of service for "some time" as it conducts an investigation into the incident in partnership with LG Energy Solution and Fluence, its engineering contractor, and makes any needed repairs.

The Moss Landing facility, which is on track to become the world's largest battery storage facility, in August announced the completion of a 100-MW expansion of the facility, bringing its total storage capacity to about 400 MW.

The company said the 100-MW battery system remained available for operation because it is located in a separate building at the Moss Landing site and was unaffected by the incident.

The merchant generator did not say what caused the overheating, but the battery com­ponents involved were made by LG, which earlier this year announced a worldwide recall of batteries produced in 2017 and 2018 due to manufacturing defects implicated in fires at other lithium-ion bat­tery facilities in the US and South Korea.

Researchers with DNV GL, a global engineering standards company, told IHS Markit's The Energy Daily last year that an independent investigation into LG battery fires in South Korea found that heavy cycling of batteries to shift solar power from low midday demand periods to high-demand evening periods could accelerate battery degradation and contribute to increased fire risk.

Vistra emphasized that the safety and accident mitigation facilities at Moss Land­ing—the biggest operating battery on Cali­fornia's grid—worked as designed, enabling the company to gain control of the overheat­ing late 4 September without any outside assistance.

Vistra did not respond to questions from The Energy Daily about whether the affected battery cells caught fire.

"However, consistent with Vistra's inci­dent response planning and out of an abun­dance of caution, the Moss Landing team did ask the local fire department, North County Fire Protection District of Monterey County, to respond to the site," Vistra said in a 5 September statement.

"Importantly, there were no injuries to the facilities' workers as a result of the incident and the situation is contained to the facility with no harm to the community," it added.

The Moss Landing outage comes as California is desperately in need of energy storage to firm its growing fleet of intermit­tent solar and wind facilities. Most notably, the California Independent System Operator (Cal-ISO), the state's grid operator, was forced to implement blackouts in the summer of 2020 when it fell short of power supplies on two hot summer evenings when demand soared as output from the state's solar farms dropped off. The blackouts occurred in part because Cal-ISO lacked sufficient storage or other resources it could tap to step in when solar resources dwindled.

In recent weeks, the California Public Utilities Commission (CPUC) and ISO have been scrambling to add resources to alleviate a new electricity supply short­age that has been aggravated by a sharp decline in available hydro-electric power due to severe drought across the West.

Longer term, the CPUC has ordered the state's utilities and other load-serving enti­ties to add thousands of megawatts of bat­tery storage over the next decade to back up the huge increase in renewables that will be needed for California to meet its goal of tran­sitioning to a zero-emission grid by 2045.

And in the absence of any other cost-effec­tive storage technology at present, states and utilities across the country are planning similar large battery installation programs to support their ambitious deployment of renewables.

McMicken fire

The overheating and fire problems with LG batteries were first illustrated in the US in April 2019, when a fire destroyed Arizona Public Service's (APS) 2-MW McMicken battery storage facility.

APS' investigation faulted manufacturing defects in a LG battery cell. The utility found "dendritic growth" in the battery cell caused a short circuit and set off "thermal runaway" that spread to other cells and modules in the storage facility, releas­ing flammable gases that exploded when firefighters entered the facility.

The root cause analysis found abnormally high dendritic growth in other LG batteries in the two-year-old McMicken facility and a sister battery storage unit at APS's Festival Ranch site.

The explosion at the McMicken facility forced APS to suspend its plans to deploy about 850 MW of batteries by 2025—one of the nation's most aggressive plans for using batteries to help integrate renewable resources—while it figured out what hap­pened and how to better address the risk of battery fires.

APS in December 2020 lifted that pause after the release of the root cause analysis and has resumed deployment of batteries under more stringent fire safety standards as part of its moves toward net-zero power generation.

Flawed manufacturing

Notably, however, LG batteries also were implicated in nearly 30 fires in energy stor­age systems (ESS) in South Korea from 2017 to 2019 that also were linked to flawed bat­tery manufacturing processes.

LG responded to the chronic problems in May by announcing it would replace batteries manu­factured between April 2017 and September 2018 and used in energy storage systems because of manufacturing defects linked with fire risks.

The company said it would conduct "global inspections, replacement, and safety-enhancing upgrades of battery management and control software" for affected ESS units in cooperation with its customers and with global product safety authorities responsible for product recalls in relevant markets.

LG also said at that time that a compre­hensive review of production and quality assurance processes following reports of lithium-ion battery fires revealed flaws in the production of electrodes in ESS batteries manufactured between April 2017 and September 2018.

The company said its replacement program would provide new batteries at no charge that incorporated manufacturing process improvements designed to enhance safety. In addition, LG said it would update battery diagnostic and control software at facility sites.

Vistra did not respond to questions 7 September about whether the batteries that over­heated at its Moss Landing site were among those recalled or modified by LG.

Investigators at DNV GL, which was hired by South Korean authorities to investigate the root cause of the fires at battery facilities there, pointed to the common practice in South Korea of cycling the lithium-ion bat­teries from close to 0% to 100% and then back down again on a daily basis as an underlying cause of failures in the battery cells that sparked the fires.

That hard-driving cycling pattern had been common in South Korean storage systems co-located with wind and solar farms to shift the output to periods of higher demand.

However, most batteries deployed to date in the US have been used primar­ily for fast-responding frequency regulation, leading to a narrower and less stressful band of cycling.

"If we start cycling those batteries as aggressively as we do in Korea, we will likely see similar failure rates," George Garaban­dic, DNV GL's energy storage leader for the Asia-Pacific region, told The Energy Daily in a January 2020 interview. "It should be expected that a higher component stress will result in higher levels of random compo­nent failures. In other, more developed ESS markets, the batteries are providing services similar to frequency regulation, and the component stress is relatively milder."

If accurate, DNV GL's assessment could prove problematic for US utility-scale battery developers, who are increasingly co-locating storage with solar generation and touting its ability to charge up during the day when the sun is shining and then discharging that power in the late afternoon and eve­ning—a cycle similar to those used at South Korean energy storage facilities hit by fires.

Most of the fires under investiga­tion in South Korea were at facilities co-located with renewable resources, according to local media.

--Originally published in The Energy Daily,


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