I. What is an energy storage system?
In analyzing energy storage processes, the defined area of objects or space used to determine the research object is called the energy storage system. It includes the input and output of energy and matter, and the energy conversion and storage devices. Energy storage systems often involve multiple energy sources, devices, materials, and processes, making them complex energy systems that change over time. Multiple indicators are needed to describe their performance. Commonly used evaluation indicators include energy density, energy storage power, energy storage efficiency, energy storage price, and environmental impact.
II. What are the components of a battery energy storage system?
The energy storage system mainly consists of a battery system, a PCS converter system, a prefabricated substation system (if any), a station service transformer system (if any), an energy management system and monitoring system (SCADA system), primary and secondary cables, etc.
1. Battery system
Currently, energy storage methods are mainly divided into three categories: physical energy storage (pumped hydro storage, compressed air energy storage, flywheel energy storage, etc.), chemical energy storage (lead-acid batteries, redox flow batteries, sodium-sulfur batteries, lithium-ion batteries), and electromagnetic energy storage. Due to economic reasons and application scenarios, chemical energy storage is the most widely used, except for pumped hydro storage. From the perspective of international and domestic markets, lithium-ion batteries are more widely used in chemical energy storage.
2. PCS converter system
A bidirectional energy storage converter (PCS) enables AC/DC conversion between batteries and the grid, facilitating bidirectional energy flow between them. Through control strategies, it manages the charging and discharging of the battery system, tracks grid load power, controls the charging and discharging power of the battery energy storage system, and controls the grid voltage under normal and islanded operation modes. It features high conversion efficiency, a wide voltage input range, rapid grid-connected/off-grid switching, and convenient maintenance. It also possesses comprehensive protection functions, such as islanding protection, DC overvoltage protection, and undervoltage ride-through (optional), meeting the requirements for grid connection and off-grid operation.
3. Prefabricated substation system (if any)
If a high-voltage (6kV, 10kV, 20kV, 35kV, etc.) grid-connected system is used, a box-type substation must be used to complete the voltage boosting task. In order to minimize electromagnetic interference and circulating current effects between the two branches, the box-type substation system uses a double-split transformer. Other parameters are not significantly different from those of wind power and photovoltaic power.
4. Station auxiliary power substation system (if any)
This power supply provides AC power to equipment within the substation, such as lighting, HVAC, maintenance, protection panels, energy storage motors in high-voltage switchgear, switch energy storage, and power supply for living and working facilities, requiring operational power. If forming a multi-energy complementary power station with wind power or photovoltaic power, it can share a single station service transformer system with the wind or photovoltaic power source. Simultaneously, the appropriate station service transformer capacity is selected based on the electricity load.
5. Primary and secondary cables
AC ZR-YJV22 or ZR-YJV23 flame-retardant cross-linked polyethylene insulated power cables feature high mechanical strength, good resistance to environmental stress, excellent electrical properties, and resistance to chemical corrosion. They are lightweight, simple in structure, and easy to use. This product is suitable for AC power transmission and distribution lines with a rated voltage of 35kV and below.
ZR-RVVP control cables are low-smoke halogen-free flame-retardant cables. These cables not only have flame-retardant properties but also low smoke emission and are harmless (with low toxicity and corrosiveness), making them suitable for locations with special requirements for cable flame retardancy, smoke density, and toxicity index.
6. Battery Management System (BMS) and Energy Management System (EMS)
The Battery Management System (BMS) primarily manages the charging and discharging protection of the battery pack. When fully charged, it ensures that the voltage difference between individual cells is less than a set value, achieving equal charging of all cells in the pack and effectively improving the charging performance under series charging methods. Simultaneously, it detects overvoltage, undervoltage, overcurrent, short circuit, and overtemperature conditions of each individual cell in the pack, protecting and extending battery life. The BMS system is provided with the lithium-ion battery pack.
The Energy Management System (EMS) primarily monitors the real-time operating status of the power plant, including system power curves, battery voltage and temperature information, cumulative processed power information, and other agreed-upon monitoring data. It can also establish remote monitoring software on the server, enabling remote control and data download, real-time alarms, and transmission to designated mobile phones.
7. Monitoring system and related access system equipment
The basic functions of a battery energy storage monitoring system include: measurement and monitoring, data processing, analysis and statistics, operation control, event alarm, protection management, human-machine interface, accident recall and historical data retrieval, historical data management, remote control and forwarding, and system maintenance.
