The security of an energy storage system does not have to be a guessing game. Customers and installers alike can rest assured by selecting and installing UL-rated systems to National Fire Protection Association (NFPA) standards. While both organizations’ energy storage standards 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 policy makers – 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 a rise in temperature that eventually leads to cell short circuit or disintegration that can cause a fire. Batteries can thermal runaway from physical damage, thermal neglect and electrical abuse, but this is unlikely when energy storage systems are tested and installed to industry standards explained below.
UL 9540 – Standard for safety of energy storage systems and equipment
To have a UL 9540 certified energy storage system (ESS), the system must use a UL 1741 certified inverter and UL 1973 certified battery packs tested using UL 9540A safety methods. It’s quite a mouthful of UL, but actually the batteries and inverter in a UL 9540 certified ESS all meet product safety standards.
When an ESS provider says it has completed UL 9540A testing methods, it does not mean it is fully certified and ready to install, Maurice Johnson, business development engineer with UL’s energy systems and e-mobility group, said in a statement. press release about the tests.
“As a test method, UL 9540A testing does not provide certification, UL marking, or pass/fail results,” he said. “The information from the UL 9540A test supports important safety decisions about how the battery ESS will be installed and used.”
UL takes the results of the 9540A testing, analyzes the ESS into a few more categories, and allows the system to be presented to installers as a UL 9540-certified ESS. UL 9540 covers any technology that stores energy in any size – not just lithium batteries in predefined cabinets.
“UL 9540 sets requirements for what we want to see happen in the energy storage system,” said Ken Boyce, UL’s senior director for principal engineering, industrial. “We look to ensure that the cells are properly proven for safety and that they are properly integrated into the system and have the appropriate software and hardware controls to control the functional safety of the unit.”
An ESS without UL 9540 certification doesn’t necessarily mean it isn’t safe, but many jurisdictions now require only certified batteries to be installed.
“It is certainly possible to develop a safe energy storage system for lithium batteries, but you have to pay attention to the safety requirements laid down in UL 9540, as lithium-ion batteries can be prone to thermal runaway. It’s important to manage that potential hazard in a safe way,” Boyce said.
UL 9540A – Test method for evaluating thermal runaway fire propagation in battery energy storage systems
While it does not provide certification, the UL 9540A test method does provide some clarity on how batteries perform in a fire. If thermal runaway occurs, this test shows how the ESS would respond. A battery may fail or fail these tests, but the results help installers design systems for the most successful performance.
“UL 9540A provides us with a very science-oriented way of demonstrating what the consequences of a thermal runaway would be,” Boyce said. “We will simulate a thermal runaway in a single cell and see if it spreads. Sometimes that’s the end there – there’s no significant effect of that cascading. But sometimes you see it happen, so then we go to the next level.”
UL 9540A tests look at the battery cell, battery module, and battery unit. The test attempts to initiate thermal runaway at the cell level, then notes how it happened and how the module responded, e.g. if outgassing occurred. Next, researchers will look at how fire spreads from unit to unit to determine the potential for an explosion. Finally, a closed room test is performed to show how a fire spreads from unit to unit and responds to fire mitigation equipment.
The results of these extreme tests help fire departments and other safety organizations both install energy storage systems and successfully suppress fires or other adverse outcomes that may occur during their use.
Many other third-party organizations, such as the International Fire Code (IFC) and the NFPA, also refer to UL 9540A test methods for their own standards.
NFPA 855 – Standard for the installation of stationary energy storage systems
This National Fire Protection Association standard focuses specifically on preventing and extinguishing ESS fires by properly installing systems and providing accurate safety labels for worst-case scenarios. NFPA installation standards are not enforceable unless approved by local jurisdiction.
NFPA 855 is largely associated with non-residential systems; the group defaults to common sense installation practices for smaller batteries. For example, if a residential ESS is installed in the garage of a house, it should be placed in such a way that the risk of an accidental collision from a vehicle is limited. There is more concern about large-scale storage systems installed both indoors and outdoors due to the greater risk of loss of property and life.
NFPA 855 requires 3 ft of space between each 50 kWh of energy storage, but the AHJ can approve closer proximity for larger storage systems based on UL 9540A thermal runaway test results. The NFPA installation standard also uses results from UL 9540A test methods to determine which safety labels and fire suppression systems are required. Labels explain what type of battery is installed and what safety precautions have already been taken, so first responders aren’t surprised when they arrive at an emergency.
Different safety installation codes and standards are used in the case of huge utility-owned energy storage sites, where the inverters and batteries are housed in separate locations, and the entire project is often far from other buildings, such as the 1600 MWh installation at Moss Landing in California.
While ESS fires and explosions are rare, it’s important to at least recognize the possibility and prepare for the worst. Installing UL-certified systems to NFPA standards ensures that using energy storage is a safe option for everyday power needs.