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Three modes of photovoltaic energy storage power station
- Aug 03, 2018 -

The energy storage technology has functions such as peak clipping, load tracking, frequency modulation and voltage regulation, and power quality control. It is an effective supporting technology for large-scale renewable energy power generation into the power grid. Therefore, it is very important to allocate energy storage systems to photovoltaic power plants. Good choice. The photovoltaic energy storage system can store excess electric energy into the energy storage battery when the photovoltaic power station encounters the abandoned light limit power generation. When the photovoltaic power generation amount is lower than the limit value or the night power consumption peak, the battery internal energy is sent through the energy storage inverter. Into the power grid, the energy storage system participates in the power grid to cut peaks and fill the valley, the energy storage system can also use the peak and valley electricity price difference to create greater economic benefits and improve the system's own adjustment capabilities.

The main modes of the energy storage system include an energy storage system disposed on the DC side of the power supply, an energy storage system disposed on the AC side of the power supply, and an energy storage system disposed on the load side.

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1. Energy storage system configured on the DC side of the power supply

The energy storage system configured on the DC side of the power supply can be mainly installed in a DC system such as photovoltaic power generation. This design can adjust the battery combined photovoltaic power generation array in the DC section of the inverter. The photovoltaic power generation system and the battery energy storage system share an inverter in the system, but the maximum power in the photovoltaic grid-connected inverter in the original system due to the difference between the charge and discharge characteristics of the battery and the output characteristics of the photovoltaic array The tracking system (MPPT) is specially designed to match the photovoltaic output characteristics and cannot meet the output characteristic curve of the energy storage battery at the same time. Therefore, such systems need to be modified or redesigned and manufactured by the original system inverter, not only need to make the inverter meet the inverter requirements of the photovoltaic array, but also need to increase the charge and discharge controller of the battery pack, and battery energy management. And other functions. Generally speaking, the system is one-way output, that is to say, the battery in the system is completely charged by photovoltaic power generation, and the power of the power grid cannot charge the battery.

The power generated by the photovoltaic array of the system is automatically DC balanced with the battery at the front end of the inverter. The main feature of this mode is that the system efficiency is high, and the power generation output of the power station can be internally scheduled by the photovoltaic power station, which can achieve seamless connection and output power. The quality is good, the output fluctuation is very small, etc., which can greatly improve the smoothness, stability and controllability of the photovoltaic power generation output. The disadvantage is that the inverter used needs special design and is not suitable for most existing photovoltaic power plants that have already been installed. Upgrade. Another disadvantage is that the battery pack in the energy storage system can only be charged by the power of the power generating unit, and the excess power of other nearby photovoltaic power generation units or power stations cannot be charged. That is to say, this kind of scheme lacks the function of power distribution inside the large power station.

2. Energy storage system configured on the AC side of the power supply

The energy storage system disposed on the AC side of the power supply uses a separate charge and discharge controller and an inverter to charge or invert the battery. This solution is actually an external energy storage device for the existing photovoltaic power generation system. Any kind of photovoltaic power station or even wind power station or other power station will be upgraded and installed to form an energy storage system in the station, or it can be built into a completely independent energy storage power station according to the needs of the power grid.

This mode overcomes the problem that the DC side energy storage system cannot perform unified power dispatching. Its system charging or discharging is completely controlled by the intelligent control system or controlled by the power grid. It can not only concentrate the excess power in the whole station to the energy storage. The system can quickly and efficiently charge, and can even dispatch the cheap low-cost excess power of the external power grid, making the system more convenient and efficient.

Another mode of the energy storage system connected to the AC side is to connect the energy storage system to the grid end. Obviously, the difference between the two energy storage systems is only the access point. The former is to connect the energy storage part to the AC low voltage side, share a transformer with the original PV power plant, and the latter is to form an independent storage of the energy storage system. Power plant mode, direct access to high voltage power grid.

The AC side access solution is not only suitable for grid energy storage, but also widely used in relatively isolated areas such as islands to form a relatively independent micro grid power supply system. The energy storage system connected to the AC side can not only be implemented on the newly built power station, but also can be easily reconstructed and added to the already built power station, and the circuit structure is clear. The power generation field and the energy storage electric field can be constructed separately. Direct direct correlation, so it is also easy to run control and maintenance. The disadvantage is that because power generation and energy storage are independent of each other, coordination and control between each other requires a special intelligent control scheduling system, so the cost is relatively high.

3. Energy storage system configured on the load side

The energy storage system disposed on the load side mainly refers to emergency power supply and movable electric equipment, such as rechargeable electric vehicles, power tools and mobile phones.