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Concept and Mode of Photovoltaic Energy Storage System

1. What is photovoltaic + energy storage?


Energy storage mainly refers to the storage of electrical energy. The combination of photovoltaic output and battery as energy storage device is photovoltaic + energy storage. Photovoltaic energy storage power stations (systems) mainly cooperate with photovoltaic grid-connected power generation applications. Therefore, the entire system includes photovoltaic module arrays, photovoltaic controllers, battery packs, battery management systems (BMS), inverters and the corresponding energy storage power station joint control power generation systems, including dispatching systems, etc.


2. Working mode of photovoltaic energy storage system


Photovoltaic power generation has the characteristics of high output level in a short time at noon, low output level in other periods, and output during the day and no output at night. The output is transferred to other time periods to reduce the peak output of the power station and reduce the abandonment of light.


In the working process of the battery energy storage system, the principle of reducing the number of charging and discharging times of the energy storage system as much as possible is to prolong the service life of the energy storage system. During the peak hours of photovoltaic power generation, the charging of the battery energy storage system is controlled to cut the output of the photovoltaic power station. After the peak period of photovoltaic power generation, the discharge of the battery energy storage system is controlled, and the discharge control of the photovoltaic energy storage system can assist in smoothing the fluctuation of the photovoltaic output and assisting the peak regulation of the system to maximize the effect of energy storage.


According to the different functions of energy storage and discharge, three working modes of the energy storage system can be divided, namely peak clipping, peak clipping + smoothing, and peak clipping + transfer.


Working mode 1: peak clipping.


During the peak output period of the photovoltaic power station, the charging of the battery energy storage system is controlled with the application target of peak shaving. After the peak photovoltaic output period, and during the photovoltaic daytime output period, the power of the battery energy storage system is controlled to amplify and discharge to the battery energy storage system. The lower limit of the SOE working range, and then the photovoltaic energy storage system stops working to ensure that the working time of the energy storage system is within the power generation time of the photovoltaic power station, without additionally increasing the working time of the photovoltaic power station, reducing the need for the photovoltaic power station due to the configuration of the energy storage system. arrangement impact.


Working mode 2: peak clipping + smoothing.


During the peak output period of the photovoltaic power station, the charging of the battery energy storage system is controlled with the application target of peak shaving. The output fluctuation of large-scale photovoltaic power plants can be divided into two categories. One is the slow change of the output of photovoltaic power plants, such as the periodic changes in the output of photovoltaic power plants caused by the alternation of day and night; A sudden drop in the output of photovoltaic power plants.


The changes in the first round are large, but the changes are slow; the changes in the second type are unpredictable and sudden. In severe cases, the output is reduced from full power to below 30% of the rated value within 1~2s.


After the peak period of photovoltaic output, the discharge of the energy storage system is controlled with the goal of smoothing the decline and fluctuation of the output of the photovoltaic power station during the alternation of day and night, and the discharge reaches the lower limit of the SOE working range of the battery energy storage system. If it has entered the night, the output of the photovoltaic power station will decrease. When it reaches 0, the SOE of the energy storage system is still greater than 0.2, and the energy storage system is controlled to discharge at the rated power and constant power until the SOE drops to 0.2, and then the energy storage system is controlled to stop working.


Working mode three: peak clipping + transfer.


During the peak output period of the photovoltaic power station, the charging of the battery energy storage system is controlled with the application target of peak shaving. The output period of the photovoltaic power station is 8:30~18:30, and the evening peak of the load occurs between 18:00~22:00. During this period, the photovoltaic power station has basically no output, which can be assisted by controlling the discharge of the battery energy storage system. System peak regulation, in order to reduce the number of actions of the photovoltaic energy storage system and simplify the operation of the battery energy storage system, control the battery energy storage system to discharge at constant power, discharge at the lower limit of the SOE working range of the battery energy storage system, and then the energy storage system stop working.

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