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Addressing Safety Concerns at Energy Storage Systems using Lithium-Ion Technology

Jens Conzen

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Jul 23, 2019

In recent months, there have been several reported fires at grid-connected lithium-ion battery energy storage facilities in South Korea and the United States. This included a fire with subsequent explosion at a relatively new 2MW installation in Arizona. These fires have raised questions about the safety of the technology and the impact on future regulation.

Lithium-ion battery technology provides a versatile energy storage option that has been successfully used for powering consumer electronics, tools, electric vehicles, as well as backup power systems. Grid scale energy storage has reached a new dimension as megawatts of electrical power are being stored. Compared to other battery technologies, lithium-ion batteries are more resilient to damage from excessive discharging and can cycle more times without significant loss of capacity. Lithium-ion batteries also have a higher energy density than traditional battery designs providing a footprint advantage.

So are these systems safe? Energy Storage Systems (ESS) using lithium Ion can be susceptible to catching fire under certain conditions. For instance, an internal failure of one or a small number of cells can lead to an internal short circuit that generates enough heat to initiate thermal runaway. Other triggering events could be overcharging, mechanical abuse, or an ordinary electrical fire inside the ESS container near the battery cells. When thermal runaway occurs, the fire propagates through an entire module unless the batteries are adequately cooled. This is mainly achieved with water spray as clean agents are typically only effective to suppress the conventional fire. Aside from the high heat during thermal runway, lithium-ion battery fires can also produce toxic and flammable gases. Upon bursting of a battery cell, the electrolyte is discharged under high pressure. The discharged cloud may be flammable and is water reactive forming hydrofluoric acid (HF) by reacting with the humidity in the air. HF is noxious and poses a serious inhalation danger. That’s where ventilation comes in.

Energy storage systems are being adapted quickly—faster than policymakers can create standards for them. The National Fire Protection Association has recently released the second draft version of NFPA 855, Standard for the Installation of Stationary Energy Storage Systems, which provides useful guidelines to suppliers, system integrators, and operators/owners. The final draft is scheduled for release and comment next year with the final version scheduled for release in 2020.

Many companies are looking to get ahead of any forthcoming regulations and assess the safety and fire protection of their energy safety systems. They start by developing a process hazard analysis at the design stage to safely mitigate any known hazards. From there they can characterize the fire, explosion, and toxic gas hazard from a lithium-ion battery failure and begin to design a system to address these failure points.