There are two ways to store energy on the power generation side of lithium batteries

　　One is that the energy storage system is connected to the AC side through a step-up transformer. The advantage of this scheme is that the capacity configuration of the energy storage system is flexible, and the energy storage and photovoltaic can be freely configured. The disadvantage is that the energy storage system needs to be separately connected to the grid, and the grid connection procedures are relatively complex. The battery charging and discharging undergo multi-level conversion, resulting in low system conversion efficiency and a lot of energy loss on the transformer;

　　The second is to connect the energy storage system to the DC side of the photovoltaic inverter. The advantage of this scheme is that the DC energy is directly stored through a first level DC-DC conversion, without being connected to the grid through a transformer, which is more efficient. The disadvantage is that a high-power DC converter DC-DC is required, and the photovoltaic and energy storage configurations need to be 1:1, which is not flexible enough. In fact, there is no need to configure so much energy storage.

　　One of the main functions of energy storage on the photovoltaic power generation side in large-scale photovoltaic power plants is to accept and smooth the grid load, and follow and track the planning curve of the higher-level grid. When the output power of photovoltaic power generation exceeds the planned curve, the excess energy is stored in the energy storage battery; When the output power of photovoltaic power generation is lower than the planned curve, the energy from the energy storage battery is input into the grid. Peak shaving and valley filling is another important function of energy storage on the photovoltaic power generation side. When the output power of photovoltaic power generation is limited, excess energy is stored in energy storage batteries; When the output power of photovoltaic power generation is not limited, the energy of energy storage batteries will be output to the grid.

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