Energy storage system safety certification: UL9540 and UL9540A standards
2025-04-25
UL 9540: Energy storage system and equipment safety standard
UL 9540 is a safety standard for energy storage systems (ESS) and equipment developed by Underwriters Laboratories (UL). It mainly targets the design, manufacturing and installation safety requirements of lithium-ion battery energy storage systems, fuel cell energy storage systems, and other energy storage technologies. This standard ensures the safety of energy storage systems when operating under normal and abnormal conditions, and is widely used in residential, commercial, industrial and grid-level energy storage systems.
1. Scope of UL 9540
This standard applies to complete energy storage systems including energy storage equipment, control systems and energy management, such as:
• Lithium-ion battery energy storage system
• Sodium-sulfur battery
• Lead-acid battery
• Solid-state battery
• Flywheel energy storage
• Supercapacitor energy storage
• Fuel cell energy storage
UL 9540 is mainly applicable to the safety certification of the following energy storage systems:
• Photovoltaic + energy storage (Solar + Storage) system
• Industrial-grade large-scale energy storage
• Grid-level energy storage
• Grid-level energy storage
2. Main test items and requirements
UL 9540 covers multiple key safety tests, including thermal runaway, electrical safety, mechanical safety and environmental adaptability tests. The main test requirements are as follows:
(1) Battery system safety
• Thermal runaway protection: The battery system will not experience thermal runaway, fire or explosion under extreme conditions.
• Short circuit test: Simulate internal short circuit conditions to ensure that the system will not cause serious safety accidents.
• Overcharge/overdischarge test: Verify that the battery system can operate safely under extreme voltage conditions.
• Temperature cycle test: Test the reliability of the battery in a long-term high and low temperature environment.
(2) Electrical safety
• Insulation withstand voltage test: Ensure the insulation reliability of high-voltage components to prevent electric shock or short circuit.
• Leakage current test: Ensure that the system does not generate excessive leakage current that affects personal safety.
• Grounding protection: Test whether the equipment can effectively conduct current to the ground in the event of a fault to avoid the risk of electric shock.
(3) Mechanical safety
• Shock and vibration test: Ensure that the energy storage system will not be damaged by vibration or impact during transportation, installation and operation.
• Enclosure protection test (IP rating): Test the system's dust and water resistance to ensure that it can still work normally in harsh environments.
(4) Environmental adaptability
• Temperature and humidity test: Simulate extreme temperature and humidity environments to verify the weather resistance of the energy storage system.
• Salt spray corrosion test: For energy storage systems in coastal areas, ensure their corrosion resistance.
• Fire and smoke test: Verify the safety of the system under fire conditions and reduce smoke and toxic gas emissions.
(5) System-level safety
• BMS (battery management system) function verification: Ensure that the BMS can monitor the battery status and provide protection against overcharge, overdischarge, temperature abnormalities, etc.
• Thermal runaway propagation protection: Ensure that thermal runaway of a single battery will not cause the entire energy storage system to lose control.
• Emergency power-off function: In abnormal circumstances, the system can automatically cut off the power supply to reduce risks.
3. UL 9540A: Thermal runaway test
UL 9540A is a special test method for thermal runaway of energy storage systems. UL 9540A is not an independent certification standard, but is used to evaluate the propagation of thermal runaway of energy storage systems. This test is usually part of UL 9540 certification and is particularly suitable for lithium-ion batteries.
UL 9540A main tests:
• Single cell thermal runaway (Cell Level Testing)
• Battery module thermal runaway (Module Level Testing)
• Battery pack/battery cabinet thermal runaway (Pack/System Level Testing)
• Thermal propagation of the entire energy storage system (ESS Level Testing)
Many local governments (such as New York City) require lithium battery energy storage systems to pass the UL 9540A test to prove that thermal runaway will not spread throughout the system.
4. Relationship between UL 9540 and other standards
UL 9540 certification usually requires the following sub-standards to be met:
• UL 1973: Safety standard for energy storage batteries (applicable to battery modules)
• UL 1741: Safety requirements for inverters and converters for energy storage systems
• UL 1998: Safety standard for software control systems
• UL 9540A: Thermal runaway propagation test (for lithium battery systems)
• NFPA 855: Fire safety requirements for energy storage systems
UL 9540 can be used in conjunction with **international standards (such as IEC 62619, IEC 62933)** to meet the access requirements of different markets.
5. Why is UL 9540 certification important?
UL 9540 certified energy storage systems have been rigorously tested and meet global energy storage system safety standards, with the following advantages:
● Meet North American market access requirements (United States, Canada, etc.)
● Reduce the risk of fire and battery thermal runaway, and improve safety
● Improve market competitiveness and enhance brand reputation
● Meet local fire regulations (such as New York, California, etc.)
● Improve market competitiveness and enhance brand reputation
● Meet local fire regulations (such as New York, California, etc.)
For lithium battery energy storage companies, energy storage equipment manufacturers and new energy project developers, obtaining UL 9540 certification is a key threshold to enter the North American market.
6. Conclusion
UL 9540 is a key safety standard for energy storage systems, covering battery, electrical, environmental, mechanical and system-level safety tests. Especially for lithium battery energy storage systems, UL 9540 certification is not only a prerequisite for market entry, but also reduces the risk of thermal runaway and fire, and improves the safety and reliability of energy storage systems.
If you are engaged in the development or export business of lithium battery energy storage systems, it is recommended to plan the UL 9540 certification process in advance and ensure compliance with relevant standards such as UL 9540A, UL 1973, etc. to enhance product competitiveness.
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