The introduction of energy storage in the energy storage technology system can effectively use power equipment, reduce power supply costs, improve system operation stability, adjust frequency, and compensate for load fluctuations. The application of energy storage technology will bring about major changes in power system design, planning, scheduling, and control.

　　1 Application of energy storage technology in power system

　　Energy storage technology has been regarded as an important part of the six major links of "collection-generation-transmission-distribution-use-storage" in the operation of the power grid. After the energy storage link is introduced into the system, demand-side management can be effectively realized, the peak-valley difference between day and night can be eliminated, the load can be smoothed, power equipment can be used more effectively, power supply costs can be reduced, and it can also be used to improve system operation stability, adjust frequency, A means of compensating for load fluctuations. The application of energy storage technology will surely bring about major changes in traditional power system design, planning, dispatching, and control.

　　2 Principles and characteristics of energy storage technology

　　Energy storage system generally consists of two parts: energy storage device composed of energy storage elements (components); grid access system composed of power electronic devices. Mainly realize energy storage, release or rapid power exchange.

　　The energy storage system has a wide range of capacity, from tens of kilowatts to hundreds of megawatts; the discharge time span is large, from milliseconds to hours; it has a wide range of applications, running through the power generation, transmission, transformation, and distribution system.

　　The main functions of the energy storage system are as follows: (1) Used for power peak shaving to solve power consumption contradictions; (2) Used on the user side to improve power supply reliability; (3) Used for renewable energy optimization and promote renewable energy development Application; (4) Used for power system stability control to improve grid security.

　　Large-scale energy storage technology is a revolutionary breakthrough to the traditional "send-and-use" power mode. It can reduce the investment in power generation equipment, improve the utilization rate of power equipment, and reduce line loss when installed near electrical equipment. Installation near big cities can improve the reliability of power supply.

　　3 Current status of energy storage technology The forms of electrical energy storage can be divided into four categories: mechanical energy storage (such as pumped water storage, compressed air energy storage, flywheel energy storage, etc.), chemical energy storage (such as sodium-sulfur batteries, flow batteries, lead Acid batteries, nickel-cadmium batteries, super capacitors, etc.), electromagnetic energy storage (such as superconducting magnetic energy storage, etc.) and phase change energy storage (such as ice storage, etc.).

　　For a long time, research on energy storage technology in power systems has focused on large-scale energy storage technology to solve the problem of system peak shaving. Recently, small and medium-sized energy storage technologies such as energy storage batteries, supercapacitors, superconducting magnetic energy storage and high-efficiency flywheels have made considerable progress, which has greatly expanded the application range of energy storage technologies. Relying on these energy storage technologies of different scales, their applications can run through all aspects of the power system's power generation, transmission, distribution, distribution and consumption, so as to comprehensively improve the operating efficiency, reliability, power quality and asset value of the power system.　　4 Power storage methods and development status

　　4.1 Compressed air energy storage power station

　　Compressed air energy storage (compressed air energy storage, CAES) is a gas turbine power plant for peak shaving. It mainly uses the surplus electricity from the grid load trough to compress air and stores it in a high-pressure sealed facility with a typical pressure of 7.5 MPa. The peak is released to drive the gas turbine to generate electricity. CAES gas storage has very little possibility of leaking and cracking, high safety factor, long life, cold start, black start, and fast response speed. It is mainly used for peak and valley power recovery adjustment, load balancing, frequency modulation, distributed energy storage and The power generation system is back-up.

　　4.2 Superconducting magnetic energy storage system

　　The superconducting magnetic energy storage system (SMES) uses coils made of superconductors to store magnetic field energy. There is no need to convert the form of energy during power transmission. It has the advantages of fast response speed, high conversion efficiency, large specific capacity/specific power, etc., which can be realized Real-time large-capacity energy exchange and power compensation with the power system. SMES can fully meet the requirements of power transmission and distribution network voltage support, power compensation, frequency adjustment, improvement of system stability and power transmission capacity.

　　4.3 flywheel energy storage

　　flywheel energy storage system is composed of high-speed flywheel, bearing support system, motor/generator, power converter, electronic control system and vacuum pump, emergency backup bearing and other additional equipment. At valley load, the flywheel energy storage system is provided by the power frequency grid to drive the flywheel to rotate at a high speed and store energy in the form of kinetic energy; when a peak load occurs, the high-speed rotating flywheel acts as the prime mover to drive the motor to generate electricity, and output through the power converter. Current and voltage. Flywheel energy storage has high power density, high efficiency, long cycle life, no pollution, simple maintenance, and continuous operation. It is mainly used for uninterruptible power supply/emergency power supply, grid peak shaving and frequency control.

　　4.4 Battery Energy Storage System

　　battery energy storage system mainly uses the oxidation-reduction reaction of the positive and negative electrodes of the battery for charging and discharging.

　　Lead-acid batteries have a shorter lifespan at high temperatures, lower specific energy and specific power, but they are cheap, low in construction cost, reliable, and mature in technology. They have been widely used in power systems. However, its cycle life is short, and there is a certain amount of environmental pollution during the manufacturing process.

　　Sodium-sulfur and flow batteries are regarded as emerging, high-efficiency and large-capacity electric energy storage batteries with broad development prospects. The sodium-sulfur battery has high energy storage density, small size, high system efficiency, and long cell life. It can be installed in stages according to the purpose and construction scale. It is very suitable for urban substations and special loads. The flow battery has small electrochemical polarization, can discharge 100% deeply, has a long storage life, and its rated power and capacity are independent of each other. The storage form can be freely designed and the shape can be freely selected according to the location of the installation.

　　4.5 Pumped Storage Power Station

　　When the pumped energy storage power station is put into operation, it must be equipped with two upstream and downstream reservoirs. The pumped energy storage equipment works in the state of the motor during the low load period, and pumps the water from the downstream reservoir to the upstream reservoir for storage. When the load peaks, the pumped energy storage equipment works on the generator. The state, using the water stored in the upstream reservoir to generate electricity. Pumped energy storage is mainly used in peak and valley filling, frequency modulation, phase modulation, emergency backup, black start and provision of system reserve capacity. It can also improve the operating efficiency of thermal and nuclear power plants in the system. 4.6 Supercapacitor Energy Storage Supercapacitor is developed based on the theory of electrochemical double layer. It can provide powerful pulse power. When charging, the electrode surface is in the ideal polarization state. The charge will attract the opposite ions in the surrounding electrolyte solution to make it attached. On the surface of the electrode, an electric double layer is formed to form an electric double layer capacitor. Due to the very small distance between the charge layers and the use of a special electrode structure, the surface area of the electrode has increased tens of thousands of times, resulting in a great electric capacity.

　　5 Prospects for the development of energy storage technology With the increasing popularity of new energy sources (wind energy, solar energy, fuel cells, etc.), as well as the urgent needs of power grid peak shaving, improvement of grid reliability and improvement of power quality, the importance of power storage systems has become increasingly prominent . Therefore, the application prospect of electric energy storage technology is very broad. The use of large-scale energy storage devices can reduce and delay the investment in power generation, transmission, transformation, and power distribution equipment, improve the utilization rate and power supply reliability of existing power equipment, and reduce power generation coal consumption and power supply line losses.

　　Once the energy storage system has a scale effect, it will produce economic benefits from the following aspects:

　　5.1 Effectively improve the utilization rate of existing power generation, transmission and distribution equipment, and change the growth mode of power construction

　　Take Shanghai as an example. At present, Shanghai’s power generation system and transmission and distribution system are planned and constructed in accordance with the highest annual electricity load. At the same time, Shanghai's load characteristics show obvious metropolitan characteristics, and the day-night peak-valley difference is increasing day by day. The current daily load rate is about 50% to 60%. Once the energy storage system has formed a scale effect, the energy storage system can be used to increase the utilization of equipment in the power generation and transmission and distribution links, and reduce the corresponding power supply and grid construction costs. This will completely change the construction model of the existing power system and promote its transformation from an extensional expansion type to a connotation synergistic type.

　　5.2 Reduce the operating costs of power generation companies and grid companies, and reduce users’ electricity costs

　　The operation and maintenance of the energy storage system is relatively simple, and the operation and maintenance costs of the power plant and the power grid can be greatly saved after being put into use. Whether it is a power plant or the power grid, the operation and maintenance are relatively complicated (p. 186) (p. 153). The energy system can save a lot of operation and maintenance costs. In order to ensure the power balance during low load conditions, most large thermal power units have to reduce their output to the minimum, and small units need to be turned on and off at night and operate in "two shifts". After the large-scale application of the energy storage system, under low load conditions, the energy storage device can be started for energy storage, and the unit can operate in a relatively economical output range, thereby obtaining higher economic benefits.

　　5.3 Reduce power outage losses

　　After the realization of distributed energy storage, users can ensure power supply through the energy storage system in some cases of grid failure and maintenance. The safety and reliability of user power consumption are greatly improved, the number of power outages (time) and power outage losses are greatly reduced, and the economic effect is The social effect is obvious.

　　At present, the biggest obstacle to the promotion and application of electric energy storage systems is the technological monopoly of a few foreign companies, which has resulted in high prices. It is necessary to promote the large-scale application of electric energy storage systems in the power grid: firstly, mastering independent intellectual property rights to make its prices drop significantly; secondly, relying on government policy encouragement and financial promotion. If the localization of the power storage system can be realized, and its cost can reach or approach the application level, then with the gradual increase in the peak-to-valley price difference and the increasing demand for power quality, the suppressed power grid's demand for the power storage system will be Get a strong release quickly.