Background

Around 5 p.m. on April 19, 2019, there were reports of smoke from the building housing the energy storage system at APS’s McMicken site in Surprise, Ariz. Hazardous Material units and first responders arrived on scene to secure the area. Approximately three hours after the reports of smoke and shortly after the door was opened, the site experienced a catastrophic failure. Injured first responders were transported to area hospitals. A thorough investigation led by APS, with first-responder representatives, the system integrator, manufacturers and third-party engineering and safety experts, was conducted to determine the cause of the incident and identify lessons that can be applied to future battery energy storage systems.



Final report of technical investigation

Following the event in April 2019, APS immediately began a collaborative effort to determine what happened and what could be learned to prevent this type of equipment failure in the future.



The investigation involved a number of key stakeholders, and APS commissioned several forensic experts and nationally recognized research institutions. APS published regular updates on this site as the investigation progressed. Once the investigative work was completed, APS chose DNV GL, based on this firm’s reputation and experience, to combine various forensic and expert inputs into the single, consolidated report published here.



Final Report: McMicken Battery Energy Storage System Technical Analysis and Recommendations (July 27, 2020)

