AES said it plans to investigate the cause of a smoldering fire at one of its lithium battery storage facilities in Chandler, Arizona.

The 10 MW Dorman battery storage facility is owned by AES and provides energy to the Salt River Project (SRP), Chandler’s local electric utility.

Chandler firefighters had kept an eye on the facility since the smoldering began on April 18, according to the Arizona Republic. Hazardous gas leaks prompted first responders to evacuate nearby homes. Firefighters later used a robot to first enter the building on April 21, according to the newspaper’s report.

On April 29, after days of not detecting smoke, firefighters turned off the facility’s fire suppression sprinklers, opened the doors and added forced air to ventilate the building and start the facility drying-out process.

The fire was declared out on May 1, and the Chandler Fire Department shifted management of the building back to AES.

“We hope to begin the investigation in the next couple of weeks, as soon as the building dries out,” said Mark Miller, AES market business leader for California and Arizona. He said the investigation into the cause will “likely take several weeks.” No date was given for when the system might come back online.

Construction on the Dorman facility began in 2018. It was completed in 2019 and provides energy storage to SRP under a 20-year agreement. The 600 square-foot building contains more than 3,000 batteries supplied by Fluence, the energy storage joint venture launched by Siemens and AES.

The 10 MW, four-hour-duration storage project was built as part of a pilot initiative so that SRP would be better prepared to scale future battery storage technologies.

In 2019 a battery storage facility built by AES and owned by Arizona Public Service (APS) caught fire in Surprise, Arizona, injuring firefighters after gases built up in the storage building and combusted violently.

According to investigation findings, the fire was caused when a rack of lithium-ion batteries supplied by LG Chem, and operated by storage company Fluence, heated up and caught fire. The fire suppressant deployed to douse the fire proved ineffective, leading to a build-up of explosive gases that ignited when firefighters opened a door, sending several to the hospital.

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