At around 10 a.m., during preparation for the start-up of a lithium-ion (Li-ion) battery energy storage system (ESS), a fire occurred on one of the containers. The system consisted of 212 containers in which Li-ion batteries were installed of total capacity 300MW/450MWh. The day was devoted to a test phase on half of the containers. At 7.20 a.m., one of them, not forming part of the test batch, was stopped manually by cutting it off from the power sources. At 10 a.m., the personnel on site detected smoke emissions from this container. The personnel electrically isolated all the containers and called the fire department. When they arrived, they established a 25m safety perimeter and cooled the area near the container. At 10.30 a.m., flames were detected on the container and, around 12 p.m., they reached a nearby container, located 15cm from the other one. Upon the recommendation of the battery manufacturer, the firefighters did not fight the fire and continued to cool the containers in the surrounding area. The fire was brought under control 6 hours after the appearance of smoke. Monitoring was organised for 3 days using thermal imaging cameras and drones.

The manufacturer said that the outbreak of fire was most likely due to a coolant fluid leak causing electric arc and a short circuit and then thermal runaway. The real-time data monitoring and acquisition system (SCADA) had to operate for 24 hours in order to report the data correctly. The SCADA system on the container where the fire started had been stopped after 13 hours, so it was therefore not possible for the safety measures to be triggered when the coolant fluid leak occurred. The distance of 15cm between the 2 containers had been approved during certification tests. The flames coming from the roof of the first container reached the second one, helped by strong gusts of wind. The upper part of the second container’s thermal roof set the internal components on fire, in particular the lighting system and plastic overpressure vents, providing a direct path for the flames and hot gases to penetrate the battery compartment. As the batteries were exposed to temperatures exceeding the temperature triggering thermal runaway (139°C), the fire developed in the second container.

The operator revised:

• the assembly and verification of the cooling circuit equipment;
• the alarms to prevent the risk of a coolant fluid leak;
• the connection time needed for information feedback from the SCADA system, from 24 hours to 1 hour;
• the design of the overpressure vents on the roof of the containers to ensure that they are heat-resistant. Under these conditions, the tests did not call into question the 15cm spacing between 2 containers.