Validating Safety at the System Level Through Extreme Testing

As energy storage systems continue to grow in scale, discussions around safety are becoming increasingly pragmatic. Rather than simply asking whether a system is certified, customers are now raising a more direct question: if the worst-case scenario occurs, how does the system respond — and can the risk still be controlled?

Recently, the SolaX ORI 5MWh large-scale energy storage system completed a full-scale system-level deflagration test with real cells under the UL 9540A:2025 proposal framework, with UL Solutions directly involved in the test design, execution and assessment. This marks the first system-level deflagration test conducted globally by UL under this proposed framework.

Recreating the most demanding system-level risk scenarios

The test was carried out on a fully integrated ORI 5MWh large-scale energy storage system. Under controlled conditions, real battery cells were intentionally driven into thermal runaway, with the emergency ventilation system kept closed throughout. The system then went through the full sequence of flammable gas release, build-up and deflagration, covering the key risk chain used in system-level safety assessment.

The test site, system set-up and operating conditions were planned by UL Solutions based on simulation work and designed to represent a highly demanding scenario. The trigger point was placed in an area where pressure waves and flame turbulence can develop more strongly, increasing the challenge for structural integrity and pressure-relief pathways.

System response aligned with design expectations

Test observations showed that during the deflagration event:

• The pressure-relief structure activated as designed

• Container doors remained closed throughout the event, with no significant deformation observed

• The container structure remained intact, with no rupture

• No components or structural fragments were ejected

• No additional risks to surrounding personnel or the environment were identified

The ORI 5MWh large-scale energy storage system’s performance under extreme conditions provides valuable engineering evidence for system-level energy storage safety.

UL Solutions engineering assessment

A UL Solutions engineer involved in the test commented: “The test was designed to optimize both the severity and realism of the deflagration scenario. However, the use of real lithium-ion battery cells inherently introduces uncertainties related to thermal runaway and free gas dispersion.

The test layout was therefore designed to minimize these uncertainties by incorporating redundant ignition sources, carefully defining the thermal runaway initiation mode of the trigger cell, and positioning the trigger cell in a location that maximizes deflagration potential, while still assessing whether the system responds according to engineering logic once deflagration occurs.

The test conditions applied to the SolaX ORI 5MWh large-scale energy storage system presented a high level of challenge to both structural integrity and safety functions, and the results provide valuable reference for understanding system-level safety boundaries.”

SolaX perspective: safety as a development baseline

SolaX R&D representatives stated: “For us, safety is not simply a compliance milestone, but a baseline that is repeatedly validated throughout the development process. Once a system is deployed, the associated risks are ultimately borne by the customer.

Identifying potential issues early and clearly defining safety boundaries through rigorous testing is our fundamental responsibility.”

Looking ahead

SolaX will continue to work closely with UL Solutions and other internationally recognized organizations to advance energy storage safety through system-level engineering validation, supporting the long-term, reliable integration of energy storage into global energy systems.