SK On said on Tuesday its energy storage system (ESS) has completed a large-scale fire test evaluation and met assessment items under UL 9540A, a North American ESS fire safety standard. The large-scale fire test (LSFT) replicates real ESS fire conditions to verify whether fire spreads to adjacent containers. It tests how far heat spreads to surrounding areas when thermal runaway occurs in one battery location.

The test was conducted under strengthened requirements. Detailed requirements were tightened in March to assess whether fire spreads based on clearer standards. The company said the heat from the ESS container where the fire occurred did not cause battery cells inside an adjacent container to go into thermal runaway, and internal container temperatures also stayed within the evaluation criteria.

SK On explained it designed the system so heat generated by the ESS is dispersed and released over a long period. It said this prevents a sharp rise in the heat release rate and lowers the risk of fire spreading to nearby containers. The company plans to accelerate its push into the global ESS market after obtaining the UL test report.

The company signed a contract in September last year to supply an ESS with a capacity of 1 GWh to U.S. renewable energy company Flatiron. In August, it signed a contract with U.S. ESS company Neovolta Power to supply lithium iron phosphate (LFP) batteries for ESS use. In South Korea, it secured 284 MW, more than half of the total 565 MW, in the second central contract market in February this year. Its Seosan plant in South Chungcheong province is converting 3 GWh of its total 7 GWh production lines into dedicated lines for ESS LFP batteries.

An SK On official said, "This test confirmed the fire safety of SK On's ESS, which suppresses fire spread and maintains key safety performance even under actual fire conditions." The official added, "We will continue to strengthen safety technology and product competitiveness to provide customer-tailored ESS solutions and expand our presence in the global market."