What should be paid attention to when using energy storage batteries off-grid or on-grid?

When industrial and commercial energy storage batteries are used off-grid, if the battery cabinet already contains PCS, an external inverter is generally not required for the following reasons:

• The PCS function covers the inverter function: PCS is an energy storage inverter, which is a key device that connects the battery system to the grid or load. It has a bidirectional conversion function and can convert the DC power stored in the battery into AC power for transmission to the grid or load. It can also convert AC power into DC power to charge the battery. This function is consistent with the core function of the inverter. For example, in industrial and commercial energy storage systems, PCS can flexibly switch between grid-connected and off-grid modes according to the control instructions of the system, complete the conversion and transmission of electric energy, and meet the power demand under different working conditions.

• System integrated design: Modern industrial and commercial energy storage systems usually adopt an integrated design concept, which highly integrates PCS with equipment such as battery cabinets. This integrated design not only improves the compactness and reliability of the system, but also optimizes the performance and control logic of the system. In an integrated energy storage system, PCS and battery management systems (BMS) work together to realize functions such as battery charge and discharge management, status monitoring, and power quality regulation, without the need for external inverters to achieve additional functions.
• Cost and efficiency considerations: If an external inverter is added to a battery cabinet system with an existing PCS, the complexity and cost of the system will increase. On the one hand, it is necessary to purchase additional inverter equipment and supporting connection cables, mounting brackets and other accessories, which increases hardware costs; on the other hand, too many device connections will increase the energy loss of the system and reduce the overall efficiency of the system. The use of a battery cabinet system with integrated PCS can effectively reduce system costs and energy losses while meeting the requirements of off-grid functions, and improve the economy and operating efficiency of the system.

1. Equipment selection and configuration

(1) Battery type and performance: Select the appropriate energy storage battery type according to the usage scenario and needs, such as lithium-ion batteries, lead-carbon batteries, all-vanadium liquid flow batteries, etc., and consider its energy density, cycle life, charge and discharge efficiency, safety and other performance indicators. For example, lithium-ion batteries have high energy density and long cycle life, but they need to pay attention to heat dissipation in high temperature environments.

(2) PCS and inverter selection: If the battery cabinet does not contain PCS, it is necessary to select a suitable PCS or inverter based on the power, voltage and other parameters of the energy storage system. The PCS should have bidirectional conversion function, complete protection function and good power quality regulation capability; the inverter should be selected according to the load type and power. For example, for inductive loads, a sine wave inverter should be selected.

(3) Capacity configuration: The capacity of the energy storage battery should be reasonably configured, and it should be calculated based on factors such as load power, power consumption time, and backup power duration. At the same time, the battery charge and discharge depth should also be considered to avoid excessive charge and discharge that affects battery life. For example, in an off-grid photovoltaic power generation system, the required photovoltaic array capacity and energy storage battery capacity can be calculated based on the local sunshine conditions and load requirements.

2. Installation and connection

(1) Installation environment: The energy storage battery should be installed in a dry, ventilated, and cool place, avoiding direct sunlight, humidity, high temperature and other environments to prevent battery performance degradation and safety accidents. At the same time, it should be ensured that the installation site meets the safety requirements such as fire prevention and explosion prevention.

(2) Electrical connection: When connecting batteries, PCS, inverters, loads and other equipment, the connection should be firm and reliable to avoid looseness that leads to poor contact, heating and other problems. The connection line should use appropriate specifications and materials to meet the current and voltage requirements of the system, and take insulation and grounding protection measures.

(3) Grid connection point selection: When connected to the grid, it is necessary to select a suitable grid connection point based on factors such as the capacity and voltage level of the energy storage system. The grid connection point should have sufficient capacity and stability to avoid impact and influence on the power grid. For example, it is generally recommended that the user-side energy storage system adopts the transformer low-voltage side access method, but the capacity and load of the transformer need to be verified.

3、System control and protection

(1) Control strategy: The energy storage system should have a complete control strategy to achieve precise control of battery charging and discharging, flexible power adjustment, and effective interaction with the grid or load. For example, control strategies based on parameters such as voltage, current, and SOC can be used to ensure the stable operation of the system and the quality of power.

(2) Protection function: PCS and inverters should have multiple protection functions such as overcurrent protection, overvoltage protection, undervoltage protection, overheating protection, and short-circuit protection. When the system is abnormal, the circuit can be cut off in time to protect the safety of equipment and personnel. In addition, DC arc protection devices should be configured to prevent DC side arc faults from causing fires and other accidents.

(3) Communication and monitoring: The energy storage system should be equipped with a reliable communication and monitoring system to achieve real-time monitoring and remote control of information such as battery status, equipment operating parameters, and power quality. Through the monitoring system, abnormal conditions of the system can be discovered and handled in time, improving the reliability and operation and maintenance efficiency of the system.

4. Safety and maintenance

(1) Safety management: Formulate a complete safety management system and operating procedures, strengthen safety training for operators, and ensure that they are familiar with the operating procedures and safety precautions of the energy storage system. During the operation of the system, obvious safety warning signs should be set up to prohibit unauthorized personnel from entering the equipment area.

(2) Firefighting measures: According to the scale and danger level of the energy storage system, configure corresponding firefighting equipment and fire extinguishing systems, such as fire extinguishers, fire hydrants, gas fire extinguishing systems, etc. At the same time, firefighting equipment should be inspected and maintained regularly to ensure that it is in good standby condition.

(3) Maintenance: Regularly maintain energy storage batteries, PCS, inverters and other equipment, including appearance inspection, cleaning, tightening connections, performance testing, etc. Timely discover and deal with equipment failures and hidden dangers, extend the service life of the equipment, and ensure the stable operation of the system.

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