3.Safety at the battery module/rack level
Thermal management and suppression of thermal runaway propagation: Unlike battery cell level safety, modules and racks need to deal with the heat and gas hazards generated by the battery itself. The release of heat from thermal runaway can cause the temperature of adjacent batteries to rise, leading to the risk of thermal runaway transmission. Moreover, module and rack designs tend towards high energy density, and the spacing between batteries becomes narrower, exacerbating this risk. The release of gases during thermal runaway poses a risk, and the emission of flammable gases may cause fires and explosions, with temperatures reaching 750-1000 ° C. The toxic compounds released, such as HF and CO, pose a threat to the environment and human health.
4.BESS architecture
4.1. Typical architecture and overall architecture of component functions: Although there are various architectural variants of battery energy storage systems, there are conceptual similarities. A typical BESS includes a battery section (battery rack), power conversion system (PCS), transformer (for grid connection), etc. The battery rack is located on the left side and contains series connected battery modules. The modules are configured in series and parallel with multiple individual batteries, providing a certain voltage range (module 20-100V, rack 200-1500V). Multiple racks are connected in parallel to achieve a total current (100-1000A). The power conversion system is located in the middle and connected to the battery rack through low-voltage DC switching equipment, including a bidirectional inverter to achieve battery charging and discharging. Its size determines the BESS power output, while controlling active and reactive power. There are multiple types (such as PCS100, PCS120) that can be extended to multi megawatt designs, and it communicates with the BESS controller to receive power setpoints. Its protection and switching mechanism is crucial for safety. Transformers and medium voltage switchgear are selected according to the requirements of grid connection (voltage, energy, and power), and are used for boosting or reducing voltage. The grid connection point is PCC, with different voltage levels and corresponding use of different switchgear.
Battery Management System (BMS): BMS is crucial for battery safety, monitoring battery voltage, current, temperature, SOC, and other states to prevent abuse. It also performs battery balancing using both passive and active balancing methods. BMS is typically designed in multiple layers, with slave BMS measuring individual battery data within the module and transmitting it to the rack BMS. The rack BMS communicates with the slave BMS and controls DC connectors or circuit breakers. The parallel connected racks are coupled through DC combiners, which provide isolation and protection and may include additional fuses and circuit breakers.
BESS controller: Integrate all components to ensure compliance with grid specifications, control charging and discharging power, receive BMS data, trigger circuit breaker operations, control fire protection, HVAC, and environmental sensors, communicate with SCADA systems, achieve smart grid integration, receive operational tasks, and send setpoints to converters.
HVAC、 Fire protection system and enclosure: HVAC maintains temperature and humidity during battery charging and discharging; The fire protection system ensures safety in case of thermal runaway or fire; The shell is easy to operate and maintain, with multiple sizes and designs (such as indoor and outdoor cabinets, containers) that can be customized, such as 10ft, 20ft, 40ft containers, etc.
4.2. System design considerations: The relationship between safety and reliability and design requirements: Safety and reliability are related and cannot be compromised. The system should be designed to “stop running” when a fault endangers safety, and to operate in “limp mode” after a fault that does not affect safety. FMEA analysis of faults is required, considering their detectability, impact on performance and safety, and whether design changes are necessary. Reliability can be estimated through various techniques (such as RBD method), taking into account component aging (MTBF calculation), design margin, software factors, etc. The design should ensure system reliability.
Factors to consider when integrating components: When integrating different components (such as new lithium-ion batteries and BMS into existing systems), in addition to basic electrical specifications, cost, delivery time, availability, warranty, and inventory, as well as supplier and product maturity, collaboration capabilities (such as sharing FMEA data), firmware modification capabilities, battery and BMS system testing (including individual and module performance, battery rack electrical testing), reliability/safety vulnerability checks (working with suppliers to consider common faults such as ground faults, protection faults, BMS communication faults, processor freezes, etc.) need to be considered. After verifying the new battery and BMS, the entire system needs to be extended with FMEA Analyze and improve system integrity through hardware and software modifications (such as adding disconnect devices, communication links, and watchdogs), ensuring safe operation and issuing warning and alarm signals. Safety standards and best practices continue to evolve with technological development, requiring professional knowledge and skills for system design, integration, control, and operation.
5.Main safety standards and regulations
Standard types and organizations: Many countries have implemented various regulations and legal requirements to ensure the safety of BESS, and provided guidelines to reduce potential operational hazards. The safety standards and specifications applicable to BESS cover battery cells, modules, racks, and system installation levels, mainly including four categories of standards: Underwriters Laboratories (UL), International Electrotechnical Commission (IEC), United Nations (UN), and National Fire Protection Association (NFPA).
6.Typical quality issues of BESS
6.1. Quality audit situation: The battery system needs to undergo factory quality audit, and a professional audit company (such as Clean Energy Associates, CEA) will conduct a comprehensive evaluation of the energy storage system to reduce operational risks. CEA’s audit of over 30GWh BESS projects identified over 1300 manufacturing quality issues, categorized by manufacturing stage into battery cell level (30%), module manufacturing level (23%), and system level (48%) issues. System level issues accounted for almost half of the total defects
6.2. Classification and Impact of Major Quality Issues
Fire safety related issues: 26% of the inspected BESS batteries have quality problems with fire detection and suppression systems, and 18% have defects in thermal management systems, which are crucial for functional safety. Malfunctions can significantly increase the risk of fire. For example, actuator failure may result in the inability to release fire extinguishing agents, unresponsive smoke and temperature sensors or improper wiring affecting smoke detection, malfunction of the fire alarm termination button may lead to misoperation (accidental release of fire extinguishing agents or misoperation of the sprinkler system), and damage to energy storage equipment.
Related issues with thermal management systems: Typical problems include valve defects and loose pipe connections leading to coolant leakage.
The root cause of system level issues is mainly due to the fact that the BESS integration process is mostly manual and labor-intensive, and upstream component defects may be overlooked in early quality checks.
7.Summary
The Importance and Security Challenges of BESS: BESS is crucial in modern energy infrastructure and has significant implications for the future transformation of sustainable energy. However, as its global deployment accelerates, safety and reliability become key issues. This article provides a comprehensive overview of key aspects of BESS security, including security considerations at all levels, standards, statistical analysis of fault events, root causes, and mitigation strategies.
Understanding and measures in terms of safety: Understanding the safety aspects from individual battery cells to the entire system is important. Lithium ion batteries require specific operating conditions, and exceeding specifications can lead to serious safety risks such as performance degradation and thermal runaway. Safety measures include the selection of appropriate battery chemical system, thermal insulation between batteries and modules, heat dissipation in modules/racks, and the use of water spray and other fire-fighting strategies to deal with combustible and toxic emissions from battery fires.
Safety design and reliability requirements: Safety cannot be compromised, and the system design should be able to enter “limp mode” or “stop” operation and issue warnings and alarms after a fault. Reliability analysis, Design for Reliability (DFR), and Failure Mode and Effects Analysis (FMEA) are crucial for the design of new BESS systems (even for existing subsystem integration), requiring specialized knowledge and skills in system design, integration, control, operation, and testing.
Fault events and response strategies: The number of BESS fault events is related to market growth, and proactive risk mitigation measures need to be taken. The root causes of faults range from battery defects to system integration and operational challenges. Implementing fault safety design, early detection systems, and strict quality control processes are key steps in preventing faults and improving system reliability.