Safety Challenges and Risk Analysis of Home Energy Storage Systems

Energy System Safety Issues

With the development of renewable energy, energy storage systems are increasingly used in power systems. However, the safety issues of energy storage systems have also become prominent.

There are many types of energy storage batteries, including lead-acid batteries, lithium-ion batteries, sodium-ion batteries, flow batteries and sodium-sulfur batteries, each with its own characteristics and suitable for different scenarios. Among them, lithium batteries have become the mainstream technical route in the field of energy storage with their high energy density, long life, high efficiency and fast response. 48V 60V 72V lithium-ion batteries are widely used in electric vehicles, consumer electronics and large-scale energy systems, promoting the development of related technologies and applications.

However, lithium-ion batteries also have some significant challenges, especially in thermal stability. Lithium-ion batteries may experience thermal runaway under extreme conditions such as high temperature, overcharge or short circuit, causing fire or lithium battery explosion. These safety hazards make lithium-ion batteries face a high risk of explosion in energy storage systems, becoming one of the main causes of safety accidents.

According to incomplete statistics, in the past five years (2019 to 20241, dozens of fires or explosions occurred in energy storage power stations around the world. Among them, accidents caused by lithium-ion batteries accounted for as high as 80%. These accidents not only caused property losses, but also may endanger personal safety, triggering widespread attention and research on the safety of lithium-ion batteries. In order to meet this challenge, the industry is actively exploring technical solutions to improve the thermal stability of lithium-ion batteries and developing new energy storage battery technologies in order to achieve higher safety and reliability.

Accident Analysis Report of Beijing Jimei Dahongmen 25MWh DC Photovoltaic Storage and Charging Integrated Power Station Project of EPRI

According to the China Electric Power Research Institute’s Beijing Fengtai District Energy Storage Power Station Fire and Explosion Accident Survey Report, the Beijing Jimei Dahongmen Power Station had an accident on April 16. The report lists eight reasons for the accident:

1. Safety quality of energy storage batteries
2. Electrical topology of energy storage system
3. Battery management system (BMS)
4. On-site layout of cables and wiring harnesses
5. Fire prevention design of power station
6. Monitoring, early warning and fire extinguishing systems of power station
7. Meteorological and environmental factors
8. On-site operation and management system of personnel

Based on the reported incidents, the causes of safety accidents in energy storage systems can generally be categorized into four main types: inherent battery risks, external safety risks, insufficient safety design and protection, and operational management factors.

1.Inherent Battery Safety Risks:

• Manufacturing Defects: Internal short circuits may be caused by issues such as metal burrs or poor electrode coating during production.
• Lithium Dendrites: The formation of lithium dendrites within the cell can pierce the separator, leading to internal short circuits.
• Battery Aging: The natural aging of batteries may compromise the overall safety of the energy storage system.

2.External Safety Risks:

• Electrical Hazards: These include overcharging, over-discharging, and external short circuits.
• Mechanical Hazards: Damage caused by crushing or penetration (e.g., from sharp objects).
• Electromagnetic Hazards: Electromagnetic interference may disrupt the normal operation of the system.
• Thermal Hazards: Excessively high or low temperatures can adversely affect battery performance and safety.
• Explosion Hazards: Under certain conditions, batteries may explode.
• Unsuitable Environmental Conditions: Adverse environmental conditions can pose serious safety risks to the energy storage system.

3.Insufficient Safety Design and Protection:

• Inadequate Insulation Monitoring: Insufficient insulation protection—such as DC contactor breakdowns, busbar insulation failures, or burnt AC input wiring—can degrade insulation performance and lead to arc faults and fires.
• Poor System Protection Coordination: Ineffective coordination among protective systems can compromise overall safety.
• System Control Failures: Failures in thermal management or other control systems can result in overheating or battery fires.
• Auxiliary Equipment Malfunctions: Failures in auxiliary devices may also affect the overall safety of the storage system.

4.Operational and Management System Factors:

• Lack of Coordination Between Systems: Insufficient communication and coordination among the Battery Management System (BMS), Power Management System (PMS), and Energy Management System (EMS), or uncoordinated operation between the Process Control System (PCS) and battery protection systems, can cause system-level conflicts. For instance, restarting the PCS without checking battery status after a fault may lead to AC/DC interface issues.
• Management System Failures: These include flawed management frameworks, poor environmental control (e.g., excessive humidity or dust), and inadequate fault reporting, which can delay maintenance and increase safety risks.
• Inadequate Operation and Maintenance of Energy Storage Stations: Poor post-deployment management and maintenance may result in unresolved operational issues, potentially escalating into serious safety hazards.

Risk Identification in Energy Storage Systems

Thermal Runaway Hazard

Thermal runaway refers to a condition where the internal heat generation rate of a battery significantly exceeds its heat dissipation rate. This results in the rapid accumulation of heat within the system, which cannot be effectively released, ultimately leading to a loss of temperature control and potentially triggering fires or explosions.

The process of battery thermal runaway is usually as follows: the single cell generates excessive self-heating due to mechanical or electrical abuse. This overheating phenomenon causes the battery temperature to rise and enter the thermal abuse stage, which triggers thermal runaway. The thermal runaway process releases flammable gases and smoke, the battery begins to burn, and triggers a chain reaction, which may eventually lead to a fire or even an explosion in the energy storage power station.

In addition to battery aging and internal defects, the following factors may also contribute to thermal runaway:

• Overcharging or Over-discharging: Charging or discharging the battery beyond its designed operational limits.
• Critical Connection Failure: Failure of electrical connection points, leading to potential safety hazards.
• Management System Failure: The Battery Management System (BMS) failing to effectively monitor and control the battery’s condition.
• Manufacturing Defects: Issues such as internal short circuits or other defects during the manufacturing process.
• Battery Aging: Over time, battery performance degrades, which may lead to internal short circuits or other failures.
• Failure of Cell Protection Devices: Protection devices may deform or fail, compromising the safety of the battery.
• High or Low-Temperature Operation: Extreme temperature conditions negatively affecting battery safety and performance.
• Battery Deformation and Leakage: Deformation of the battery casing or leakage of internal liquids.
• Gas Leakage or Release of Combustible Gases: During combustion, batteries may release flammable gases, posing additional risks.

Electrical Hazards

Electrical hazards are one of the most serious safety risks in energy storage systems. As the capacity and voltage of energy storage systems continue to increase, the system voltage has gradually risen from lower levels to 1500V DC. In electrical safety, any voltage exceeding 60V DC is considered hazardous, and accidental contact with live parts can lead to electric shock risks.

Therefore, energy storage systems must have effective electrical isolation measures to prevent direct or indirect contact with the electrical components during operation. For example, the risk of electric shock posed by a reduction in insulation resistance. Insulation resistance indicates the integrity of insulation materials; when cables or connections suffer from damage, aging, or degradation of the insulation layer, the insulation resistance may decrease. In such cases, damage to the insulation layer can expose the conductors inside the cables, leading to leakage currents. This leakage increases the risk of electric shock for maintenance personnel.

Additionally, energy storage systems typically contain a large number of auxiliary electrical devices, and the installation environment is often complex. Unexpected events, such as high voltage, large currents (e.g., lightning or surges), or the aging of equipment and cables leading to failure of protection elements, may result in malfunctioning protection functions or abnormal insulation, leading to electric shock and other safety incidents.

Functional safety hazards: Functional safety is an important part of energy storage system safety, due to the risks caused by the failure or failure of the controlled equipment and its related systems.

Unsuitable working environment:

Risk Assessment of Energy Storage Systems

The safety of energy storage systems is a comprehensive and complex issue that applies to the entire life cycle of electrochemical energy storage systems, i.e., from the conceptual design and development stage of the energy storage system, the system manufacturing stage, the product operation and use stage, the service and maintenance stage to the final decommissioning stage.

Energy storage system safety risks may depend on many factors, including installation location, chemistry and size/scale (such as electricity), and need to be evaluated accordingly. The safe location of solar energy battery storage systems can be for home use, industrial and commercial applications to large-scale systems for the grid; these risks need to be evaluated accordingly.

When doing system risk analysis, the IEC 62933-5-1 standard provides many methods: top-down analysis methods and bottom-up analysis methods, such as the common FMEA analysis, fault tree analysis, HAZOP analysis, and STAMP. Through a series of analysis methods to identify potential risks, and then through the safety system design and electronic circuit development of the safety protection mechanism, reduce measures to make it reach our acceptable level.

Risk Mitigation Measures for Energy Storage Systems (ESS)

Safety issues are the red line of product quality, and ensuring the safety of energy storage systems has become a major challenge for the sustainable development of the energy storage industry. Due to the particularity of energy storage products, their safety needs to be achieved by combining multiple safety functions. As described in ISO/EC Guide 51, the risk reduction measures taken in the energy storage design process are “inherent”, “safety design”, “protective devices” and “end-user information”. Additional measures for the use phase (lifecycle safety management) are also described in the ISO/IEC 51 Guide.

The design of energy storage systems not only needs to start from the technical level of system and components, but also should consider how to predict and identify potential risks in advance, provide active protection, and solve problems at the front end when failures occur. Even in extreme cases of accidents, it can provide a bottom-up capability to ensure the safety of personnel and property.

Intrinsic Safety Design for Energy Storage Systems (ESS)

• Reasonable selection of subsystems
• Protection function design
• System function safety design
• Structural design
• Electrical design
• Fire protection design
• Ventilation and explosion relief design, etc.

Guarantee and Protection Measures

• Internal faults of subsystems cannot spread to the outside of the subsystem;
• High-voltage system, prevent remote dangerous operation;
• All components with dangerous voltage due to single insulation faults must be grounded and lightning protected according to relevant standards;
• Overcurrent protection must be provided at the external connection of the battery subsystem;
• Connection faults of the subsystems of the energy storage system must not cause dangerous situations, and the loading and unloading of batteries must be carried out using appropriate lifting equipment;
• The system casing or bracket must be made of non-combustible materials; The battery area, charging equipment area, and disconnection and discharge circuit area must be divided into fireproof zones inside the system;
• Auxiliary, control and communication system fault protection: must Meet single fault safety, no danger will occur even if the power supply is interrupted or fluctuates;
• Environmental hazard protection: outdoor energy storage systems must meet at least IPX4, and salt spray protection is required for installation near the sea;
• Both the DC and AC sides must have ground fault protection and alarm functions;
• There must be an audible and visual alarm when the battery is overcharged: the overcurrent situation inside the battery subsystem must be reported;
• The system must be equipped with a combustible gas detection system and provide audible and visual alarms;
• The system should be equipped with a ventilation system and meet the following requirements: The ventilation system must ensure the appropriate temperature inside the cabinet: strong exhaust must be provided when natural ventilation is insufficient; the vents must be able to prevent the spread of fire and the inflow of water;

Operation And Maintenance, Employee Training, Information Provided to End Users

• Safety information provided to users: warning signs and signals, labels indicating dangerous parts on site, sound and light alarm devices, safety design process flow chart;
• On-site operation must take precedence over remote operation to protect the safety of on-site workers: a safety emergency plan should be prepared; overcurrent protection must be provided at the external connection of the battery subsystem;
• Operation and maintenance manuals should be provided to the owner, and the manufacturer or system integrator must develop a regular maintenance plan;
• The manufacturer must provide guidance on the capabilities and authorization requirements of personnel operating equipment or safety systems;