By Kelly Pickerel
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The safety of an energy storage system doesn’t have to be a guessing game. Both customers and installers can take comfort by choosing UL-rated systems and installing to National Fire Protection Association (NFPA) standards. Although energy storage standards from both organizations are relatively young (UL 9540 began in 2016; NFPA 855 in 2020), they received input from hundreds of stakeholders, including engineers, manufacturers, first-responders and safety policymakers — all in an effort to prevent loss of life and property.
Many safety concerns, especially with lithium-based batteries, relate to thermal runaway — when a battery experiences an increase in temperature that eventually leads to cell short-circuiting or disintegration that can spark a fire. Batteries can go into thermal runaway through physical damage, thermal neglect and electrical abuse, but the chances of this are slim when energy storage systems are tested and installed to the industry standards explained below.
UL 9540 – Standard for Safety of Energy Storage Systems and Equipment
In order to have a UL 9540-listed energy storage system (ESS), the system must use a UL 1741-certified inverter and UL 1973-certified battery packs that have been tested using UL 9540A safety methods. It’s quite a UL-mouthful, but basically, the batteries and inverter inside a UL 9540-certified ESS have all met product safety standards.
When an ESS provider says it has completed UL 9540A test methods, that doesn’t mean it’s fully certified and ready to install, said Maurice Johnson, business development engineer with UL’s energy systems and e-mobility group, in a press release about the tests.
“As a test method, UL 9540A testing does not provide a certification, UL Mark or pass/fail results,” he said. “The information from UL 9540A testing supports important safety decisions about how the battery ESS will be installed and used.”
UL takes the results of the 9540A tests, analyzes the ESS in a few more categories and allows the system to be presentable to installers as a UL 9540-certified ESS. UL 9540 covers any technology that stores energy in any size-rating — not just lithium batteries in predetermined cabinets.
“UL 9540 has requirements for what we want to see going on inside the energy storage system,” said Ken Boyce, UL’s senior director for principal engineering, industrial. “We look at making sure the cells are appropriately proven for safety and that they’re being integrated into the system the right way and have the right software and hardware controls to govern the functional safety of the unit.”
An ESS without UL 9540 certification does not inherently mean it is not safe, but many jurisdictions now require that only certified batteries be installed.
“It’s certainly possible to develop a safe lithium battery energy storage system, but you have to pay attention to those safety requirements that are codified in UL 9540 because lithium-ion batteries can be susceptible to thermal runaway. It’s important to manage that potential hazard in a safe manner,” Boyce said.
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