Battery energy storage is an integral part of the modern energy landscape. Not only does it support commercial and industrial applications, it also enhances the flexibility and resilience of the grid. By enabling grid operators to store energy generated from solar and wind during peak production hours, battery energy storage systems (BESS) can release that energy when demand arises.
For professionals in the energy storage field, especially developers and general engineering contractors, it is critical to understand the essential components of a battery energy storage system and their interrelationships. While various battery chemistries exist, this guide will focus on lithium-based systems, which dominate the market, accounting for over 90 percent of deployments.
Key Components of Battery Energy Storage Systems (BESS)
Battery Systems
The battery is the core component of a BESS and is used to store energy for later use. It consists of a fixed number of lithium-ion cells arranged in series and parallel within a frame to form a module. These modules are stacked and combined to create a battery rack. The voltage and current levels required by the BESS can be achieved by connecting the battery racks in series or parallel. If you are interested in the differences between these configurations, you may wish to view a comparison of series and parallel battery systems. Keheng’s battery systems utilize UL1642 cells, UL1973 modules, and UL9540A test racks to ensure safety and quality.
Battery Management System (BMS)
The Battery Management System (BMS) is critical to any lithium-based energy storage system. As the “brain” of the battery system, the BMS protects the battery from potential damage in various operating scenarios. It ensures that the battery operates within predetermined limits, with key parameters such as state of charge (SoC), state of health (SoH), voltage, temperature, and current. Advanced BMS solutions from companies such as EVESCO have a multi-tiered architecture that provides real-time monitoring and protection at the cell, module, pack, and system levels. The BMS continuously evaluates the battery’s state, analyzes the data using application-specific algorithms, manages the battery environment, and maintains balance. This is critical for effective thermal management and helps prevent thermal runaway. A well-designed battery management system is essential to any lithium-ion battery energy storage system, ensuring safety and longevity.
Power Conversion System (PCS) or Hybrid Inverter
In a BESS, batteries store and deliver power in direct current (DC), while most electrical systems and loads operate as alternating current (AC). Power conversion systems (PCS) or hybrid inverters are required to bridge this gap. These devices are more versatile than standard inverters and are capable of bi-directional power conversion. This means that DC power from the battery can be converted to AC power for the grid or electrical loads, and AC power can be converted to DC power to charge the battery. This capability allows the BESS to be charged and discharged efficiently. The PCS can be configured in various modes to accommodate the different charging and discharging strategies required for a particular BESS application. For optimal performance, the PCS or hybrid inverter must be able to access the battery’s state to manage its operation effectively.
Battery Energy Storage Systems (BESS) are complex systems that require precise management to ensure efficiency and safety. The power conversion system (PCS) is at the heart of the system, which determines when to charge and discharge the battery. For example, if a battery’s Depth of Discharge (DoD) is set to 90%, the PCS will ensure that discharge stops when the State of Charge (SoC) reaches 10%. The system can be steered by a preset policy, an external signal, or an energy management system (EMS).
The PCS has two primary configurations: ac-coupling and dc-coupling. The BESS is connected to an external AC-side solar PV system via a dedicated inverter in the AC-coupled setup. In contrast, the DC-coupled system integrates the batteries with the solar PV on the same DC bus, sharing the hybrid inverter between the PV and the BESS.
The controller is the equivalent of the brain of the BESS, managing and protecting key components while communicating with external devices such as meters. It integrates with third-party SCADA and EMS for comprehensive data collection and energy management with multiple levels of protection, including overload and reverse power protection.
The HVAC system is critical to maintaining optimal temperatures within the BESS, preventing overheating and extending battery life. Effective thermal management ensures battery cell performance and longevity.
Fire suppression systems activate during a thermal runaway event to provide additional safety for the battery. These systems can be triggered by gas, smoke, or heat detection, releasing an extinguishing agent such as Novec1230 or FM-200, which absorbs the heat, thus improving safety standards.
SCADA (Supervisory Control and Data Acquisition System) enhances monitoring within the BESS. It communicates with the controller and BMS to track battery status and can issue commands from the HMI (Human Machine Interface). Most BESS can be integrated with third-party SCADA systems to ensure complete management and control.
At Keheng, we prioritize these components to provide efficient and safe energy storage solutions that meet international standards.
Energy Management System (EMS)
Energy Management Systems (EMS) play a key role in the operational direction and scheduling of Battery Energy Storage Systems (BESS). By connecting directly to the Power Conversion System (PCS)/Hybrid Inverter and the Battery Management System (BMS), the EMS can coordinate the various field components and take into account external data from the grid, transformers, photovoltaic (PV) arrays, and loads.
The EMS is responsible for determining the optimal timing and method of discharge, a decision influenced by specific applications such as peaking, load shifting, or self-consumption. By optimizing the performance of the BESS, the EMS successfully balances application cycling data and battery life with return on asset investment while adhering to the operational constraints imposed by the BMS and the PCS/hybrid inverter. In addition, the EMS system collects and analyzes BESS performance data to simplify reporting and forecasting.
These elements ensure battery energy storage systems’ safety, efficiency, and value. Various other differences may exist between battery energy storage systems from different manufacturers. At Cohen, our battery energy storage systems come in rugged, containerized housings, and all of our 5-, 10-, and 20-foot systems are shipped fully assembled to provide appropriate plug-and-play solutions. Learn how battery energy storage systems work in our dedicated blog.