With the arrival of the era of the smart grid, the role of energy storage technology is becoming increasingly obvious, and its application scope has been involved in all aspects of power generation, transmission, distribution, and use. Electric energy storage not only has the technical characteristics of rapid response and two-way regulation but also has the advantages of strong environmental adaptability, flexible configuration mode, and short construction period. It is expected that by 2050, China’s energy revolution will have achieved phased results, and the proportion of new energy in energy production and end-consumption will exceed “50%”. The energy storage market will have a huge space.

In the past three years, under the joint influence of multiple factors such as technological progress, demand growth, and policy support, the application of electric energy storage technology in China has developed rapidly and begun to take shape. On the power side, several power generation enterprises in China have taken the lead in exploring the application of energy storage technology, playing its role in smoothing output fluctuations, tracking scheduling plan instructions, improving the consumption level of new energy, and participating in joint frequency modulation auxiliary services. On the power grid side, to cope with the development of new energy and the construction of UHV power grid, it is urgent to improve the flexibility and stability of power grid regulation, give full play to the role of energy storage technology in peak and frequency regulation, system backup, black start and improvement of power quality. On the user side, the “valley charging, peak discharging” mode under the peak-valley price difference is mainly adopted to improve the electricity fee structure of power users, and the energy storage technology can play its role in peak filling, demand management, demand response, and virtual power plant. With the commercialization of energy storage technology, the scale of energy storage projects will gradually increase, and the application market areas of energy storage will be more clearly defined.

1 Main technology of energy storage

Traditional energy storage technology is mainly based on water storage and electrochemical energy storage. With the country’s emphasis on the energy storage industry, the acceleration of technology updates, and the development of manufacturing processes, a variety of new energy storage technologies have been obtained in actual projects. Application, and play an important role in all aspects of the power system. Energy storage technology can be divided into three categories according to its energy conversion mechanism: physical energy storage, chemical energy storage, and other energy storage. Table 1 shows the comparison of the characteristics of each energy storage technology type.

Tab.1 Performance comparison between and among different energy storage technologies

A pumped-storage power station is a “giant battery” in the power system. The power station converts the generated electric energy into potential energy of water at night when the power consumption is low and converts the potential energy into electric energy to ensure the operation of the load during peak power consumption or power shortage. . Its characteristics are: the technology is relatively mature, the service life is long, and the power capacity is large, but its response speed is relatively slow, and the requirements for site selection are relatively high.

The main components of compressed air energy storage include compressor, compressed air storage, combustion chamber, expander, and motor/generator. In the energy storage process, air enters the compressor from the atmospheric environment, is compressed into high-pressure air, and then stored in the compressed air storage; in the energy release process, the high-pressure air in the compressed air storage first enters the combustion chamber and mixes and burns with fuel. It becomes high-temperature and high-pressure air and then enters the expander to perform work and output electrical energy. Its characteristics are: mature technology, large power capacity, long service life, high efficiency, but high investment cost, must meet certain geological conditions (pressure sealed caves).

Lithium-ion batteries are considered to be the battery system with the best overall performance at the moment. They have been widely used in energy storage power stations and have rapidly developed into a new generation of power sources for information communications, electric vehicles and hybrid vehicles, and aerospace and other fields. Its characteristics are high energy density, long cycle life, small size, lightweight, but high cost, slow capacity decline, and intolerance of overcharge and over-discharge.

The energy storage medium of the all-vanadium flow battery is an aqueous solution containing vanadium ions. In the solution, the valence state of vanadium ions can be changed, through the change of valence state, the mutual conversion between chemical energy and electric energy can be realized, and the mutual conversion between charging and discharging of the energy storage system can be realized. Its characteristics are long service life, high safety, large capacity, but high cost, which is greatly affected by the price change of vanadium.

Lead-carbon battery is a capacitive battery technology evolved from the traditional lead-acid battery. Active carbon is added to the negative electrode of the lead-acid battery, which significantly improves the life of the lead-acid battery. Its characteristics are low cost, safety, easy availability of raw materials, reliability, mature industrialization technology, but low energy density.

Supercapacitors can meet the requirements of many fields, and the current market scale and application fields are constantly growing. Its characteristics are high output power, fast response, maintenance-free, long life, and wide operating temperature range, but if used improperly, it will cause electrolyte leakage.

2 Development status of energy storage technology

The strategic layout of my country’s energy storage industry can be traced back to the “Renewable Energy Development Guidance Catalogue” issued in 2005; energy storage was included in the “Twelfth Five-Year Plan” outline in 2011; the National Energy Administration issued the first energy storage industry in 2017 The guiding document “Guiding Opinions on Promoting the Development of Energy Storage Technology and Industry” pointed out that energy storage should be transitioned from R&D demonstration to the initial stage of commercialization during the “13th Five-Year Plan” period, and the initial stage of commercialization to scale during the “14th Five-Year Plan” period The development of transformation. Since the development of energy storage technology, the main scientific research investment has been centered on the field of electrochemical energy storage, especially the R&D and application of lithium-ion batteries, lead-carbon batteries, and all-vanadium flow batteries have reached the international advanced level.

3 Application of energy storage technology

According to the survey, as of the end of 2019, the cumulative installed capacity of energy storage projects in operation worldwide was 183.1 GW, an increase of 1.2% year-on-year; the cumulative installed capacity of energy storage projects in operation in China was 32.3 GW, accounting for 18% of the world. It is estimated that by the end of 2020, China’s energy storage market will accumulate

The installed capacity of the projects put into operation will reach 45.2 GW. On this basis, the energy storage market will expand three times by 2024. In 2019, my country’s electrochemical energy storage technology has made important progress, with a cumulative installed capacity of 1,592.7 MW, accounting for 4.9% of the country’s total energy storage capacity, a year-on-year increase of 1.5%. In terms of geographical distribution, it is mainly concentrated in new energy-rich areas and load centers; in terms of application distribution, user-side energy storage installed capacity accounts for the largest proportion, accounting for 51%, followed by power-side auxiliary services (24%) and grid-side (Accounting for 22%). Due to the large distance between my country’s energy center and power load center, the power system has always followed the development direction of large power grids and large units and is operated by the centralized transmission and distribution mode. With the rapid development of renewable energy and the acceleration of the construction of UHV power grids, society’s requirements for power quality continue to increase, and the application prospects of energy storage technology are very broad. In the application scenarios of the power supply side, grid side, user side, and microgrid, the functions of energy storage and its effect on the power system are different.

The accumulative installation scale of electrochemical energy storage power station in China in recent years

3.1 Power side

In the traditional power generation field, energy storage mainly participates in auxiliary frequency modulation services to make power generation more controllable. It is widely used in Shanxi, Inner Mongolia, Shandong, Anhui, and other places. In these areas, there are more assembled thermal power generators, less water and electricity, and insufficient flexibility of the power supply system. In this scenario, a power-type energy storage battery needs to be configured, which has a fast response speed, realizes integrated scheduling with the thermal power unit, improves the overall response performance of the unit, and increases the utilization of the equipment.

3.2 Grid side

On the grid side, energy storage is mainly used to provide auxiliary support for peak and frequency modulation, provide emergency protection, and ensure safety and stability. Since 2018, grid-side energy storage projects have developed rapidly, driving the growth of electrochemical energy storage projects. China’s first 100-megawatt grid-side energy storage power station cluster and also the world’s largest electrochemical energy storage power station cluster should be put into operation in Jiangsu Born. At the same time, grid-side energy storage projects in Henan, Hunan, Gansu, Qinghai, and other provinces have also been gradually implemented. China Southern Power Grid completed the 4 MW/16 MW·h Shenzhen Baoqing Battery Energy Storage Power Station in 2010, becoming China’s first megawatt-level peaking and frequency modulation lithium battery energy storage power station; Henan Power Grid has built 100 MW/100 MW·h grid side storage Energy power station; Hunan Changsha battery energy storage power station project is divided into two phases, the scale of the first phase is 60 MW/120 MW·h, which has been completed and put into operation; Dalian, Liaoning, 200MW/800 MW·h flow battery energy storage peak-shaving power station is National large-scale chemical energy storage demonstration project, the first phase of 100 MW/400 MW·h is under construction.

In the UHV power grid, energy storage is an important means to provide system backup and emergency protection and to ensure the safe operation of the power grid. It is bound to accelerate development and can play multiple roles at the same time. The grid-side large-scale energy storage project of Italy’s Terna company can simultaneously undertake multiple tasks such as primary and secondary frequency modulation, system backup, reducing grid congestion, and optimizing power flow distribution through the switching of different operation control modes, and ultimately improve the stability of grid operation effect. In the distribution network, energy storage can effectively supplement the lack of power supply, and control the “low voltage” or distributed energy connection in areas with weak distribution networks.

The “high and low voltage” problems caused by the entry can simultaneously solve the distribution network power supply problems such as seasonal load, temporary power consumption, and unqualified capacity expansion and expansion, effectively delaying new investment in the distribution network. Chicago Electric Power uses recyclable energy storage equipment to delay transformer upgrade investment, which is a typical application for delaying the construction of power transmission and transformation facilities on the grid side.

3.3 the user side

The energy storage system installed at the load end can maintain the power quality, ensure the safety and stability of the power supply, and reduce the influence of voltage fluctuation on the power quality. User-side energy storage can be used for peak clipping and valley filling, demand response, and electricity demand management for traditional loads. Peak clipping and valley filling are suitable for users who consume a large amount of electricity during peak hours and is the most common commercial application at present. The electricity cost is reduced through “valley charging and peak discharging”. Demand response obtains benefits by responding to grid dispatching and helping to change or shift power load. Demand management reduces demand and electricity bills by reducing spikes. Jiangsu Wuxi Xingzhou Industrial Park Energy Storage System Project (20 MW/160 MW·h) is the country’s largest commercial operation of user-side energy storage, and is also the first grid acceptance project by the State Grid Jiangsu Electric Power Company’s “Grid Connected Management Regulations for Customer-side Energy Storage System”. User-side energy storage can also be combined with distributed renewable energy for integrated optical storage and charging and storage applications. Jiading Anting Integrated Charging, Changing and Storage Power Station Project integrates multiple functions such as EV charging station, electrical changing station, energy storage station, and battery echelon utilization. Jiangsu Chuniushan Island Energy Comprehensive Utilization Micro-grid Project is composed of energy storage equipment, wind, optical, and diesel engines, and is the first AC-DC hybrid intelligent micro-grid in China. However, the current domestic user side storage also face challenges: one is the user side storage environment is complex, all kinds of different user demand for energy storage, site, security issues such as energy storage project is to promote the user side of common problems, combined with the relevant standard is not clear, can be replicated in the project of low, unskilled link authors is difficult; Second, the fluctuation of electricity price also affects the income level of user-side energy storage. In the past two years, the industrial and commercial electricity price has been reduced by 20%, which directly reduces the arbitrage space of peak-valley price difference for user-side energy storage projects.

3.4 Microgrid

As the development direction of future power grids, microgrids play an important role in improving energy supply efficiency, reducing losses, and providing efficient and convenient renewable energy. With energy storage as the core means, it can aggregate multiple energy storage resources such as interruptible loads and electric vehicles, coordinate distributed power generation, build virtual power plants, and participate in demand-side response and power market transactions. Microgrids are classified into off-grid microgrids and grid-connected microgrids according to their connection to the large grid. The 1.2 MW/1.8 MW·h Renewable Energy Local Area Network Project in Nima County, Tibet is currently located in the highest altitude and worst-environment area in the world. It is composed of a variety of battery energy storage systems, diesel engines, and photovoltaics. The parallel and off-grid switchable energy storage project in Lianyungang, Jiangsu realizes real-time monitoring of user load and can adjust the operation status of energy storage at any time to ensure the reliability of user power supply.

The application of energy storage to off-grid microgrids can improve the stability of distributed energy and avoid transmission pressure and power loss caused by long-distance transmission to the main grid; it can continue to provide part of the power to the main road at night or during the maintenance of distributed energy, reducing Power failure time: The energy storage system can store the distributed power in the microgrid when the energy is sufficient, release energy when there is an energy shortage, and maintain the internal energy balance. Energy storage is applied to grid-connected micro-grids, which can stabilize the output power of the power supply, regulate the output active power and reactive power, ensure the safe and stable power consumption of the load, and effectively solve the voltage when the large power grid fails or the power quality cannot meet the requirements. Power quality problems such as dips.