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What Are the Types of Photovoltaic Energy Storage?

1. Grid-connected photovoltaic energy storage system:

The electricity generated by photovoltaics can be used during the day and night. The distributed general metering is used during the day, and the grid electricity is still used at night. After adding energy storage, the energy storage system can be discharged at night.

The grid-connected photovoltaic power generation system is directly connected to the distribution network, and the electric energy is directly input into the power grid. At present, there is no energy storage system configured. With the serious phenomenon of photovoltaic "abandoning light and limiting electricity", and the large fluctuation of the power output of the photovoltaic power generation system, etc. With the increasing restrictions on the utilization and promotion of renewable energy, the deployment of energy storage in grid-connected photovoltaic systems has become one of the current directions of large-scale photovoltaic energy storage systems.

2. Off-grid photovoltaic energy storage system

Off-grid photovoltaic power generation system is also known as independent photovoltaic power generation system. Compared with grid-connected photovoltaic system, independent photovoltaic system refers to a photovoltaic system that operates independently without being connected to the grid. It is mainly controlled by PV modules and DC/DC charging. It consists of inverter, off-grid inverter and load.

The off-grid system consists of the following parts: battery components, photovoltaic charge and discharge controllers, battery packs, off-grid inverters, and AC/DC loads. The main function of the photovoltaic charge and discharge controller is to control the charging and discharging of the battery, and to protect the battery from overcharging and discharging. Off-grid inverter, the function of off-grid inverter is to convert DC power into AC power and provide it to the device used by the load.

3. Photovoltaic energy storage microgrid

Photovoltaic energy storage microgrid consists of five basic parts, including: solar cell array, grid-connected inverter, BMS management system, battery pack, and AC load. The system adopts the hybrid power supply of photovoltaic and energy storage system. When the mains power is normal, the photovoltaic grid-connected system and the mains supply power for the load; when the mains is out of power, the energy storage system and the photovoltaic grid-connected system jointly supply power, and the system is also equipped with monitoring , heat dissipation, fire protection, security and other devices, the whole system is controlled by the monitoring and management system, and the work of each component is coordinated through the network.

Photovoltaic energy storage microgrids usually have two operation modes: grid-connected operation mode and island operation mode. Energy storage plays an integral role in both modes of operation.

In the grid-connected operation mode, a large number of distributed small-capacity power sources are merged into the power consumption side, which leads to increased uncertainty in the power system, and intensifies the contradiction between the balance and coordination of power generation and power consumption. The distributed photovoltaic or wind power in the microgrid has the characteristics of randomness, volatility and intermittence. The energy storage system can smooth the power output of these distributed power sources, maintain the stability of the microgrid, and cooperate with the optimal scheduling of EMS. The economical operation of the microgrid can also be realized.

In the island operation mode, the microgrid loses the reference of the large grid, and the energy storage system can assume the role of the main power source for the voltage and frequency reference. When the island is isolated, the energy of the microgrid comes from the distributed electric energy and the energy storage system. The output fluctuation of the distributed energy makes it difficult to match the load demand. Therefore, a photovoltaic energy storage system with a certain capacity is equipped in the microgrid system to suppress the increase in volatility. 

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No.1, Lane 97, Siming East Road, Yinjiang Town, Haishu District, Ningbo City, Zhejiang Province
No.1, Lane 97, Siming East Road, Yinjiang Town, Haishu District, Ningbo City, Zhejiang Province