Exploring Microgrids and the Role of Energy Storage System

 Microgrid is a form of power grid that is different from traditional power grid. With the continuous in-depth research on microgrids in various countries around the world, although their definitions are different, their purposes are similar, such as improving the safety of the power system, ensuring the reliability of power supply, improving power quality, and improving the utilization of various energy sources. Rate. Based on these functional requirements, it is required that the microgrid can be connected to the grid and run on the grid, but it can also be cut off from the grid and run independently, which greatly improves the power supply reliability of the grid and the security of the power system. For the power grid, the microgrid can not only absorb energy from the grid, but also quickly switch its own state according to the operating status of the grid, choosing whether to cut off the connection with the grid or absorb energy from the grid to supplement its own needs: for power users , Microgrids meet some of their specific needs, such as increasing the reliability of power supply, reducing power supply distance, and thereby reducing power transmission line losses.

3 The necessity of energy storage system

Electric energy storage technology is very important to achieve the basic functions of microgrids. Why microgrids need to store electrical energy is mainly due to the following four reasons:

(1) To ensure the reliability of the power supply system;

(2) To ensure the quality of power supply;

(3) In order to improve the comprehensive utilization efficiency of electric energy;

(4) To improve the grid connection performance of various new energy sources. Therefore, a high-performance energy storage system is a powerful guarantee for the microgrid to realize its own functions.

3.1 Types of energy storage systems

Energy storage technology has been developed for a long time and comes in various forms. In addition to lead-acid batteries and lithium batteries that are often seen in daily life, there are also pumped energy storage, flywheel energy storage, superconducting magnetic energy storage, Superconducting capacitor energy storage, vanadium flow batteries, sodium sparse batteries, nickel metal hydride batteries, etc. The international mainstream batteries include lead-acid batteries, lithium-ion batteries, nickel-metal hydride batteries, etc. Flywheel energy storage, superconducting magnetic energy storage, and superconducting capacitor energy storage are still in the research stage and have not been applied on a large scale. Lead-acid batteries have been used on a certain scale in microgrid energy storage systems, but due to limitations of their own characteristics, some shortcomings are slowly emerging.

3.2 Characteristics of traditional energy storage systems-lead-acid batteries

Lead-acid batteries have relatively high requirements for ambient temperature: The representative of traditional energy storage systems is lead-acid batteries. Lead-acid batteries have relatively high requirements for ambient temperature, which means the environmental requirements for their use situations have been increased.

Lead-acid batteries have high requirements on power distribution rooms: the power distribution equipment of a system mainly includes power supply equipment, and the area and weight of the battery room in the power supply equipment cannot be ignored.

The high-rate discharge performance of lead-acid batteries is poor: when the operating mode of the microgrid is switched from connected to the grid to independent operation, the energy storage system will flow a large current in a short period of time, which requires the energy storage system to have high Rate discharge performance, while the performance of lead-acid batteries in traditional energy storage systems is poor.

The monitoring of lead-acid batteries is inaccurate: The monitoring system of lead-acid batteries is mostly based on voltage, and the accuracy of this method is very limited, resulting in a large amount of energy stored in the energy storage system after long-term use. deviation.

Lead-acid batteries pollute the environment: Because lead-acid batteries contain lead that pollutes the environment, improper production and waste disposal can cause serious pollution to the environment.

3.3 Application prospects of lithium iron phosphate batteries in microgrids

3.3.1 Electrochemical principle of lithium iron phosphate battery:

The positive electrode material of lithium iron phosphate battery is lithium iron phosphate (lithium peroxide compound), and the negative electrode material is graphite or coke. Lithium iron phosphate battery is a type of lithium battery. It is named after the positive electrode material of lithium iron phosphate battery.

3.3.2 Characteristics of lithium iron phosphate battery:

High energy density: Energy density can indicate the amount of energy stored in unit volume or weight. The energy density of an electrochemical battery refers to the electrical energy that the unit volume or mass of the battery can provide to an external load. Under the same weight, the energy density of lithium iron phosphate batteries is 3 to 5 times that of lead-acid batteries. That is to say, when the battery rated capacity is the same, lithium iron phosphate batteries will be much lighter than lead-acid batteries, and their weight will be relatively reduced. Requirements for support strength.

Long service life: The life of a recyclable battery refers to the number of cycles that the battery can be charged and discharged normally. The life of a lead-acid battery is about 500 times, while the life of a lithium iron phosphate battery can reach 1,600 times, and the capacity can be maintained at 80%. Phosphate The life of lithium iron batteries is significantly longer than that of lead-acid batteries.

Safety: The safety issues of lithium batteries have always been the key reason hindering their development, and lithium iron phosphate batteries completely solve the instability factor of lithium compounds. Lithium cobalt oxide and lithium manganate will explode under specific conditions, such as collision. etc. The lithium iron phosphate battery has been carefully designed and passed strict performance and safety tests. It will not explode in severe collisions, penetrations, etc.

No memory effect: If a rechargeable battery is fully charged for a long time without being used, its capacity will be relatively lower than the rated capacity value. This is the memory effect. Lead-acid batteries have an obvious memory effect. After testing, lithium iron phosphate batteries basically have no memory effect.

3.3.3 Disadvantages of lithium iron phosphate batteries. The cost of lithium iron phosphate batteries remains high because their material is lithium metal and the processing technology is not mature enough. In addition, the capacity of lithium iron phosphate batteries needs to be further improved. Before the energy management system and battery charge and discharge balancing functions of lithium iron phosphate batteries are perfected, they are not suitable for large-scale use in microgrid systems.

While technologies such as fuel cells, vanadium batteries, and flywheel energy storage are not yet mature, and the shortcomings of traditional lead-acid batteries are becoming more and more obvious, lithium iron phosphate batteries, as the representative of current electrochemical battery technology, have gradually matured and their applications have also matured. Slowly gained popularity. National policy support has accelerated the development of lithium iron phosphate batteries. The price of lithium iron phosphate batteries will also slowly decrease with the development and popularization in the future. It will become the mainstream battery in future energy storage systems with its superior performance, injecting fresh blood into the microgrid energy storage system and further enhance the microgrid. overall performance.

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