Analysis and countermeasures of safety problems in battery energy storage power stations

0 Preface

With the continuous commissioning of battery energy storage power stations, their safety issues have gradually become prominent. Since 2018, there have been 23 serious fires in the energy storage industry in South Korea, and many fires have occurred in the energy storage industry in my country after 2017, such as the automatic generation control (AGC) frequency modulation project of a power plant in Shanxi and a user in Yangzhong, Jiangsu Fire in the side energy storage project. Therefore, carrying out research on the safety of battery energy storage power stations has important practical significance for promoting the sustainable and healthy development of battery energy storage power stations.

1 Development status of battery energy storage

The battery energy storage is composed of many electrochemical units connected in series and parallel, and each unit is charged and discharged through the oxidation-reduction reaction of the positive and negative electrodes to realize the mutual conversion of electric energy and chemical energy. The characteristics of the battery energy storage power station are: the power and capacity can be flexibly configured according to different application requirements, the charging and discharging are fast, the location is less restricted by geographical conditions, and it is suitable for large-scale applications and mass production.

At present, there are various types of battery energy storage technologies, including lithium batteries, flow batteries, sodium-sulfur batteries, lead-acid batteries, etc. The technical indicators of the above types of batteries are different, and the comparative analysis can be found in the literature.

Battery energy storage power stations can be flexibly configured on the power supply side, grid side, and load side of the power system to meet the needs of differentiated energy storage applications. The typical application scenarios of battery energy storage in different configuration locations are shown in Table 1.

Although the application scenarios of battery energy storage are diverse, they mainly include three parts: battery, power transformation, and civil construction. The battery part includes battery modules, thermal management systems, battery management systems, two-way converters, energy management systems, etc. composed of single cells in series and parallel. The substation part includes electrical primary part (transformer, outlet, etc.) and secondary part (central control system, fire fighting system, etc.). The civil engineering part includes electrical battery room or outdoor battery pack foundation and factory related projects. Fire accidents are an extreme and representative safety accident of battery energy storage power stations, which are characterized by strong destructiveness, large economic losses, and high social attention. Table 2 shows the statistics of fire accidents in battery energy storage power stations that have been published in recent years.

It can be seen from Table 2 that from the point of view of fire locations, fire accidents of battery energy storage power stations are mainly concentrated in South Korea, while power station fire accidents have also occurred in the United States, Japan and China. From the perspective of energy storage types, the main type of battery energy storage technology is lithium batteries. This is because lithium batteries account for the largest proportion of installed capacity among all types of batteries; on the other hand, because there are many exothermic reactions inside lithium batteries, thermal runaway is prone to occur under certain conditions.

2 Safety risk factors of battery energy storage power station

The safety risk factors of battery energy storage power stations mainly include fire, explosion, poisoning, electric shock, and burning. Among them, the fire risk is particularly prominent.

2.1 Fire

Fire risks include not only traditional transformer fires and cable fires, but also battery fires. Compared with water-based batteries such as flow batteries and lead-acid batteries, organic lithium batteries have a more prominent fire risk. Under abusive conditions such as overcharge and overdischarge, short circuit, squeeze, etc., a series of exothermic reactions such as the reaction of the positive and negative electrodes with the electrolyte and the decomposition of the electrolyte occur inside the lithium battery, causing the thermal runaway of the battery and leading to fire. Lithium battery fire has the characteristics of fast fire speed, strong toxicity of thermal decomposition products, and difficulty in extinguishing fire.

In addition to lithium batteries, sodium-sulfur batteries have a greater fire risk. When the sodium-sulfur battery is running, once the ceramic electrolyte is damaged and a short circuit is formed, the liquid sodium and sulfur at high temperature will directly contact, and a violent exothermic reaction will occur. This kind of exothermic heat will instantly generate a high temperature of 2000°C, which is quite dangerous.

2.2 Explosion

The explosion risk mainly includes the explosion of the battery body and the explosion of the substation equipment.

(1) The battery body explodes: After the thermal runaway of the lithium battery occurs, a large amount of alkane combustible gas will be generated. If the energy storage device is arranged indoors, when the combustible gas reaches a certain concentration, it will explode when exposed to an open flame. In addition, the aqueous solution of flow batteries and lead-acid batteries will explode after hydrogen evolution after overpressure electrolysis.

(2) Explosion of substation equipment: If the step-up transformer of the energy storage system is equipped with oil, the internal fault of the transformer will cause the arc to heat up, which may cause combustion and explosion.

2.3 Poisoning

The risk of poisoning is mainly reflected in the toxic smoke produced by the burning of the battery and the crystals produced by the dissolution.

When a lithium battery burns, a large amount of gas is produced, mainly combustible gases such as hydrogen and methane, and toxic gases such as hydrogen chloride and hydrogen fluoride. Toxic gases will have a strong irritation effect on the eyes and respiratory mucosa, and can cause respiratory inflammation, pulmonary edema, ulcers, etc.

The all-vanadium redox flow battery will dissolve out when the indoor temperature is poorly controlled, and produce vanadium pentoxide, vanadium trioxide and other salts, among which the precipitated crystals are highly toxic. The precipitated crystals have a damaging effect on the respiratory system and skin, and can cause inflammation of the respiratory tract, severe itching of the skin, and kidney damage.

2.4 Electric shock

The battery energy storage system is an object containing high-energy substances. When it is not powered on or the system is turned off, some components may still be in a live state. When touching the system, if the corresponding protective equipment is not worn, electric shock is very likely to occur.

2.5 Burning

The risk of burning mainly comes from corrosive battery electrolyte or electrode materials. If the corrosion resistance of the materials and processes of the electrolyte transportation pipeline, storage tank, and battery casing does not meet the requirements, it will cause equipment corrosion; if long-term severe corrosion occurs, leakage of electrolyte or electrode materials will occur, such as the electrolysis of flow batteries Liquid transportation pipelines, liquid storage tanks, etc. have leaked due to long-term severe corrosion. The positive active materials of sodium-sulfur batteries are liquid sulfur and sodium polysulfide molten salt. Because sulfur is corrosive, the battery casing is prone to leakage. If the power station operation and maintenance personnel do not wear protective clothing or protective gloves during normal maintenance or accidents, it may cause burns and injuries.

3 preventive measures

The safety risk factors of battery energy storage power stations are diverse, and the occurrence of extreme accidents such as fires and explosions can cause serious property losses and casualties. Researchers have carried out a number of valuable studies on the safety of battery energy storage and achieved many results, but there are still many shortcomings. In the follow-up, the following work should still be done.

3.1 Research on multi-dimensional fire prevention and control technology for lithium battery

In order to reduce the risk of lithium battery fires, it is necessary to carry out a series of fire prevention and control technology research from the "source-early warning-extinguishing" multi-dimensionality. In terms of source, focusing on the three elements of ignition source, fuel, and oxidizer that need to be met in the event of a fire, the basic events that have a large impact on battery fire risk (electrode materials are easy to decompose, electrolyte is flammable, etc.), and targeted high melting point SEI membranes are developed. , Flame-retardant electrolyte, etc., to improve the intrinsic safety of batteries. In terms of early warning, collect data such as smoke, battery surface temperature, voltage, and current before battery fires, and use big data technology to extract relevant characteristic quantities of battery fires, and strive to find and deal with them early to avoid accidents or expansion. In terms of extinguishing, although existing experiments have proved that heptafluoropropane has a fire extinguishing effect on single cells and battery clusters, heptafluoropropane has not extinguished the fire in the prefabricated lithium battery cabin fire accidents that have occurred, and a large amount of water was finally used to extinguish the fire. Research on the effectiveness and boundary conditions of large-capacity lithium battery fire extinguishing agents can shorten the fire time and reduce fire losses.

3.2 Establish a layered linkage emergency mechanism for battery energy storage power stations

In order to reduce the loss of battery energy storage power station accidents, it is necessary to develop a layered linkage emergency mechanism for energy storage power stations. In terms of stratification, for various types of safety accidents, according to the characteristics of the accident, the accident level is divided, and the emergency plan for each level of accident is formulated in a targeted manner to improve the accuracy and scientificity of the plan, and reduce the accident loss. In terms of linkage, once extreme accidents such as fires and explosions occur, they will cause serious economic losses, and will affect social order and pollute the natural environment to a certain extent. Therefore, it is necessary for extreme accidents to formulate involving electricity, public security, fire protection, environmental protection, and hospitals. , Publicity and other multi-departmental linkage accident emergency plans to reduce the social impact of the accident and reduce environmental pollution. In addition, it is necessary to establish an accident investigation system to find out the cause of the accident, clarify the responsibility for the accident, and carry out the accident investigation and property damage compensation in a timely manner.

3.3 Develop safety technical standards for battery energy storage power stations

In order to better guide the sustainable and healthy development of the battery energy storage industry, and timely summarize the advanced experience of the leading regions in energy storage development, it is necessary to formulate safety technical standards for battery energy storage power stations as soon as possible, clarify equipment requirements, fire protection configuration, operation and maintenance procedures, etc. In view of the fact that the operating characteristics of battery energy storage are closely related to the type of energy storage technology, application scenarios and other factors, it is advisable to have both common energy storage standards and individual energy storage standards under different technology types and application scenarios in the safety technical standards.

4 Conclusion

First, it summarizes the development status of battery energy storage power station from the main technology types, typical application scenarios, energy storage system composition, and energy storage power station fire accident statistics; then, the five major safety risk factors of battery energy storage power stations (including fire and explosion , Poisoning, electric shock, scorching, etc.); finally, it puts forward suggestions for conducting multi-dimensional lithium battery fire prevention and control technology research, establishing a layered linkage emergency mechanism for battery energy storage power stations, and formulating safety technical standards for battery energy storage power stations. The sustainable and healthy development of battery energy storage power stations provides a useful reference.

Information source: Electric School

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