How Sungrow kept ESS safety intact under forced thermal runaway

Sungrow residential system completes UL 9540B ESS safety trial

Sungrow has reported that its SBH Series: Residential ESS has passed the world’s first UL 9540B large-scale fire test for residential energy storage systems of 20kWh and below, conducted by UL Solutions, setting out a new reference point for residential ESS safety.

The company stated that this development follows two earlier real-unit combustion verification tests on utility-scale storage units.

Sungrow explained that it has extended this approach to the residential sector as home energy storage becomes more common and concern about safety incidents grows.

The manufacturer framed the UL 9540B result as evidence that the SBH system can manage thermal runaway and restrict fire spread in demanding test conditions.

UL 9540B standard focuses on thermal runaway

According to Sungrow, UL 9540B is a safety standard designed for residential energy storage systems up to 20kWh capacity.

The test forces fully charged systems into thermal runaway to assess how they handle flammable gas build-up, venting and ignition.

UL 9540B evaluates whether a system can prevent fire spread, explosions and other secondary hazards under these conditions.

Sungrow said the SBH system was exposed to a 24 hour trial with no external intervention.

During this period, test parameters included closely spaced battery units, disabled active fire suppression and repeated ignition triggers.

The company reported that the SBH system met all evaluation criteria over the full duration of the test.

Design features limit fire spread and heat transfer

Sungrow attributed the SBH Residential ESS performance in the test to features such as cell-level fire-resistant insulation, bottom heat dissipation and multi-directional pressure relief.

When a unit entered thermal runaway, flames were confined to the pressure relief area of the cabinet.

Adjacent units recorded internal surface temperatures of 21°C, below the 154°C venting threshold defined for the test.

Eave temperatures reached 35°C, which was also well under the 150°C limit specified in the standard.

System self-extinguishes and avoids explosion risk

The company stated that structural design choices were intended to promote heat dissipation and thermal isolation between modules.

In the UL 9540B trial, thermal runaway remained confined to the bottom module within the SBH system.

With fire suppression kept offline, open flames self-extinguished within one hour of ignition.

Further ignition attempts over the remaining 24 hours produced no re-ignition of the system.

Sungrow added that no additional combustion events, explosions or projectile hazards occurred during testing while the active suppression system stayed disabled.

The cabinet structure remained intact, which the company said shows the design’s focus on fire resistance, explosion management and mechanical stability.

Broader ESS safety approach and previous testing

Sungrow noted that the SBH Residential ESS had already completed the UL 9540A Thermal Runaway Fire Propagation Test before the UL 9540B assessment.

The company positions the combination of UL 9540A and UL 9540B results as a demonstration of system-level control from individual cells through to the full enclosure.

Sungrow stated that it aims to keep developing safety-focused technologies for energy storage as residential adoption grows.

The manufacturer added that it sees adherence to demanding standards as a way to increase confidence among homeowners in residential ESS installations.