If lithium-ion battery fires are near impossible to completely prevent, then containing thermal runaway events is crucial. Battery energy storage system (BESS) provider Viridi recently hosted a live fire demonstration to show how properly engineered cell modules can prevent flame propagation.
“The real problem is not the thermal runaway event,” Jon Williams, CEO Viridi told pv magazine USA. “It’s the propagation of a fire from one cell to another. That’s where you get catastrophe.”
During the live demonstration portion of Viridi’s battery safety event, held on May 15 at its 43-acre technology center in Buffalo, NY, in partnership with the Soteria Battery Innovation Group, technicians initiated a thermal runaway event in a standard battery pack, resulting in cell-to-cell propagation. The test of a second pack equipped with Viridi’s thermal isolation and anti-propagation barriers confined the fire to the triggered cell without affecting the others.
“When you set off a 50 kWh pack and you witness the energy and the smoke and the gas that come out of that pack, you have a tremendous respect for that technology,” Williams said. “The good news is it’s really energy dense. On the flip side, it’s really energy dense.”
While there are many strategies for reducing the risk of thermal events, from battery chemistry selection to managing the operational environment, the fact is when you have a large installed base in the field something is going to happen.
Williams said JR Linna, Viridi’s head of research and development, told him that there is a probability of failure for of one in so many million cells no matter who makes them. Because at some point, you can get a short that creates enough heat and sends the cell into a catastrophic failure no matter how many sensors you put on it.
Eventually, Williams related, an event is going to run past all the safeties. He wondered how that can be stopped, but Linna said it really can’t be stopped.
For this reason, Williams said his company’s approach is to start with an effective chemistry and then engineer the strongest containment package for it. Viridi originated in 2018 making battery packs for the construction industry, where Williams says equipment is routinely roughly handled. The company produces a battery container made from quarter-inch, grade 50 steel as the first line of defense against thermal events. The goal was to take physical damage out of the equation.
“In the compact construction market, equipment gets beat up pretty bad,” he said. “They lift stuff up on buildings, they put it on the back of trucks, they drop it off stuff, it falls in ditches, it goes into ponds. Compact construction equipment are really just fancy hammers; they beat them to death.”
In addition to reducing the risk of physical damage to the BESS unit that might trigger a fire, the containment system is designed to prevent propagation of a fire in one cell from affecting adjoining cells. As calculated above, as some point a battery is going to short or otherwise fail in such a way as to produce a thermal event. Since it is not always possible to predict where the failure will occur, every cell package must be as strong as possible.
Williams explained that Viridi’s BESS modules are designed to contain the three aspects of a thermal runaway event: the tremendous heat (upwards of 700 degrees Celsius); particulates exploding out; and a concussion wave. Fluid-based heat sinks produce channeled steam that prevents adjacent cells from rising over 170 degrees Celsius, Williams said. Spacers between the cells dissipate concussive force upwards to prevent it from compressing the sidewalls of adjoining cells.
Fire safety of lithium-ion batteries is a growing concern to a widening range of stakeholders beyond manufacturers and users, increasingly including people who live among vehicle batteries and BESS installations. As a result, first responders, regulators and codes and standards organizations are struggling to catch up with appropriate rules and techniques.
Earlier this month, BESS provider Sungrow announced that its liquid-cooled PowerTitan 2.0 system had received approval from the New York City Fire Department that clears the way for deployment of its lithium-ion system within the city. Last year, Sungrow had hosted its own fire test to demonstration the thermal management capabilities of the PowerTitan.
In that test, which was conducted a test facility in China and live-streamed to stakeholders, explosion relief panels atop the unit in which the fire was set automatically vented the fire upward to prevent it from spreading to adjacent battery units. The test event unfolded without intervention by personnel or fire suppression systems until the fire burned itself out.
According to Mandy Zhang, Sungrow’s battery storage product manager for overseas regions, the widening installation of lithium-ion batteries in many fields is making any fire incident highly publicized. This leads to a perception of increased fire risk.
“We believe the industry’s focus on fire risk is mainly due to a lack of understanding of fire in energy storage systems,” Zhang told pv magazine USA. “Statistical data shows that the actual fire risk is relatively low. Reports from organizations like the National Fire Protection Association and the U.S. Consumer Product Safety Commission support this.”
Zhang believes that current fire safety certifications and standards in certain regions are lagging behind the rapidly increasing installed base of lithium-ion battery storage. She said that battery manufacturers must work with relevant standards bodies to keep them up to date on battery storage and management systems.
John Zahurancik, president, Americas, of battery-maker Fluence Energy, agrees that expertise needs to flow readily between supplies, contractors, operators and first responders to prevent thermal events from making the news and warping public perceptions of lithium-ion battery safety.
“When things don’t go well, we have to talk about that in the spirit of, hey, everybody shouldn’t have to learn this lesson on their own,” Zahurancik told pv magazine USA. “We’re part of the American Clean Power Association and, one of its big pushes is to collect some of this information and propagate the best safety approach.”
Industry is responding with more intensive testing and evaluation methods for BESS. In March UL Solutions unveiled its new UL 9540A methodology to determine a battery technology’s susceptibility to thermal runaway.
Nevertheless, Viridi’s Williams said the BESS industry and its regulators are still coming to grips with how to manage thermal events and how to manage BESS more broadly.
“All of the testing that happens right now is observational testing,” he said. “So you can pass 9540 and still have an explosion later due to something unseen. We need a conversation around that. We haven’t even started to scratch the surface of the storage we need in this country, so there is a long way to go there.”
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