Faithful Markets Live readers may recall a series of posts last year about a fire at the Victorian Big Battery (VBB) last year, which burned for three days.
A recently released investigation found the fire spread from the roof of one Megapack inside a neighbouring Megapack due to windy conditions near Geelong. Tesla had never tested for wind gusts above 20 kilometres per hour (km/h), and has now agreed to change the design of Megapacks after what happened to the VBB.
The VBB has since started operating and is managed by French company Neoen.
The 300 Megawatt VBB is constructed out of 212 Tesla Megapacks, which all arrived in Australia pre-manufactured in cabinets.
After the fire broke out on 30 July 2021, the Country Fire Authority attended but allowed the fire inside two Megapacks burn for three days, as recommended by Tesla. No one was injured and the fire did was limited to two cabinets, despite Megapacks being installed only 15 centimetres apart from each other.
“The origin of the fire was Megapack 1 and the most likely root cause of the fire was a leak within the liquid cooling system of Megapack 1 causing arcing in the power electronics of the Megapacks battery modules,” a recent report found.
“This resulted in heating of the battery module’s lithium-ion cells that led to a propagating thermal runaway event and the fire.”
However, investigators also found strong winds pushed fire from the roof of Megapack 1 onto the top of Megapack 2, which set on fire “the plastic overpressure vents that seal the battery bay from the thermal roof”.
Local investigators found Tesla’s own fire testing only allowed for winds of 19.3 km/h, as required for US certification. However, the winds in Geelong that day reached between 37 and 56 km/h.
“As such, the wind conditions during the VBB fire appear to have identified a weakness in the Megapack’s thermal roof design (unprotected, plastic overpressure vents in the ceiling of the battery bays) that allows Megapack-to-Megapack fire propagation,″ the report found.
Investigators have suggested three start-up procedure changes, three firmware changes, and that all Megapacks be installed with steel vent shields in the roof to prevent fire and heat entering the battery. This will now become standard on all Tesla Megapacks.
“Since the VBB fire, Tesla has devised (and validated through extensive testing) a hardware mitigation that protects the overpressure vents from direct flame impingement or hot gas intrusion via the installation of new, thermally insulated, steel vent shields,” the report noted.