The battery energy storage system BESS consists of two parts, the DC side and the AC side.
The DC side of the system comprises the battery compartment, which includes equipment such as batteries, temperature control units, fire protection systems, confluence cabinets, and containers. On the other hand, the AC side consists of the electrical compartment, housing components like energy storage converters, transformers, and containers.
In operation, batteries on the DC side generate direct current power. However, since the grid operates on alternating current, the system must convert this DC power to AC through a converter to enable power interaction with the grid.
Battery energy storage system BESS classification
According to the electrical structure, large-scale energy storage systems can be divided into:centralized, distributed, intelligent string, high-voltage cascaded, distributed.
(1) Centralized:
These systems typically consist of a low-voltage, high-power, boost-type centralized grid-connected battery energy storage configuration. Here, multiple battery clusters connect in parallel before linking to the Power Conversion System (PCS). The PCS prioritizes high power and efficiency, and the industry is currently promoting the 1500V solution.
(2) Distributed:
This type adopts a low-voltage, low-power, distributed boost grid-connected energy storage approach. In this design, each battery cluster connects to a dedicated PCS unit, and the PCS units adopt a low-power, distributed layout.
(3) Intelligent string type:
Building upon the distributed energy storage system architecture, this type incorporates innovative technologies such as battery module-level energy optimization, single-cluster battery energy control, digital intelligent management, and a fully modular design. These features enable battery energy storage systems to operate more efficiently.
(4) High-voltage cascaded high-power energy storage system:
This design uses a single-cluster battery inverter and connects directly to the power grid at voltage levels of 6/10/35 kV or above without requiring a transformer. A single unit in this system can reach a capacity of 5 MW/10 MWh.
(5) Distributed type:
In this configuration, multiple DC-side branches are connected in parallel. Each battery cluster has a DC/DC converter added at its outlet to provide isolation. Subsequently, these DC/DC converters are consolidated and connected to the DC side of a centralized PCS.
The battery energy storage technology route iteration revolves
(1) Security
Safety remains the most critical concern for energy storage power stations in the industry. Potential hazards in electrochemical energy storage facilities include electrical fires, battery-induced fires, hydrogen explosions in case of fire, and system abnormalities.
When tracing the root causes of safety incidents, we usually attribute them to battery thermal runaway. This thermal runaway can result from mechanical abuse, electrical abuse, or thermal abuse. Therefore, to prevent safety issues, operators must strictly monitor battery status and avoid conditions that could trigger thermal runaway.
(2) High efficiency
Battery cell consistency is a key factor affecting system efficiency. This consistency depends on battery quality, the energy storage technology solution adopted, and the battery’s operating environment. Moreover, as the number of charge-discharge cycles increases, differences between batteries gradually become apparent.
Additionally, variations in the actual operating environment during operation further exacerbate differences among multiple batteries. As consistency issues become more pronounced, they challenge the Battery Management System (BMS) and may even introduce security risks.
Regarding series mismatch between battery modules: the available capacity of series-connected batteries can only reach that of the weakest module, preventing other batteries from delivering their full capacity.
Similarly, in parallel mismatch between battery clusters: the available capacity of parallel-connected clusters is limited to the weakest cluster, thereby underutilizing the capacity of other batteries.
Furthermore, differences in internal resistance cause circulation among batteries. This circulation raises core temperature, accelerates aging, increases system cooling load, and reduces overall efficiency. Consequently, designers should maximize battery consistency in both design and operational plans to enhance system efficiency.
(3) Low cost
The cost of an energy storage system depends on initial investment and cycle life. Multiple factors affect battery cycle life, including material aging and degradation, charge-discharge systems, operating temperature, and cell consistency. For instance, when the temperature difference within a container exceeds 10 °C, battery life may shorten by over 15%. Similarly, temperature variations between modules can also reduce overall system lifespan.
Thus, battery energy storage systems should extend cycle life by optimizing charge-discharge strategies, minimizing temperature differences, and improving cell consistency.
