Energy storage technology is an important part of smart grid technology. Combined with the actual situation in China, the paper expounds the role of energy storage technology in the strong smart grid, the principle of energy storage technology, the commonly used energy storage technology and development status, points out the development prospect of China's energy storage industry, and proposes to promote the large capacity energy storage industry. Policy recommendations for development.
The power production process is continuous. Power generation, transmission, substation, power distribution, and power consumption must be balanced at all times. The load of the power system has peak-to-valley difference, and there must be a large spare capacity, resulting in low efficiency of system equipment operation. The application of energy storage technology can fill the peaks of load peaks, improve system reliability and stability, and reduce system standby demand and power outage losses. In addition, with the increasing scale of new energy power generation and the continuous development of distributed power generation technology, the importance of power storage systems has become increasingly prominent.
The application of energy storage technology is to add a stored energy link to the traditional power system production mode, so that the original almost completely rigid system becomes flexible, and the safety, reliability, economy and flexibility of the grid operation will be Greatly improved. Therefore, some people regard the energy storage technology as the sixth link in the power production process, and the application prospect of power storage technology is very broad.
I. The role of energy storage technology in a strong smart gridQuality, self-healing, safety, cleanliness, economy and interaction are the set goals of China's smart grid. The energy storage technology, especially the large-scale energy storage technology, has many characteristics that can be widely used in power generation, transmission, distribution and power consumption. Application, energy storage technology is one of the key technologies to build a smart grid and achieve its goals.
1.1 The role of energy storage technology in power system stability
The application of energy storage technology can change the thinking mode of traditional power system stability control, understand the stability problem of power system from a new perspective, and seek a method that may completely solve the stability of power system.
In a conventional power system, the dynamic unbalanced power caused by any small disturbance will cause oscillation between the units, and as long as the energy storage device is large enough and the response speed is fast enough, the system power can be completely balanced under any circumstances. It is an idea of ​​actively stabilizing the power system. Since the stabilizing control device associated with the energy storage technology does not have to interact with the excitation system of the generator, it is convenient to use the most effective portion in the system for suppressing the oscillation. At the same time, since the control amount generated by the stable control device can directly act on the source that causes the system to oscillate, and accurately compensate the unbalanced power, the influence of the change of the operating state of the system on the control effect of the control device can be less or even not considered. Therefore, the parameter setting of the device is very easy, and the robustness to the change of the operating state of the system is also very good.
1.2 The role of energy storage technology in new energy generation
The lack of fossil energy supply has become a bottleneck for global economic development. At the same time, the environmental pollution caused by the use of fossil energy has been highly valued by the world. Actively developing new energy and energy storage technologies and reducing human dependence on fossil energy has become a hot topic in the industry and the scientific and technological community.
In renewable energy, wind energy and solar energy are rich in sources, inexhaustible, inexhaustible, and there is no concern about environmental pollution or pollution during use. However, wind energy and solar energy are intermittent and unstable. Defects such as sex and uncontrollability, in order to ensure the balance and continuity of power supply, energy storage devices become key components of wind power generation and photovoltaic power generation systems. Therefore, while using solar energy and wind energy, we must pay attention to the development of energy storage technology.
In recent years, especially after the promulgation of the "Renewable Energy Law of the People's Republic of China", China's wind power generation and photovoltaic power generation industry has developed rapidly, but there are still technical bottlenecks in large-scale development of new energy sources, mainly the grid-connected technology of wind power generation and photovoltaic power generation. Intermittent problems in power generation require mature energy storage technologies to solve them. Therefore, while the installed capacity of new energy sources is increasing, it is necessary to simultaneously increase the energy storage capacity and effectively improve the power output quality.
1.3 The role of energy storage technology in distributed generation
In today's society, the quality and safety and reliability requirements of power supply are getting higher and higher. The traditional large-grid power supply mode cannot meet this requirement due to its own defects. At present, the combination of large power grid and distributed power generation is recognized by many energy and power experts in the world as the main method to save investment, reduce energy consumption, improve power grid safety and flexibility, and is the development direction of the power industry in the 21st century.
Distributed generation refers to a smaller set of generators that are placed directly in the distribution network or distributed near the load to meet the needs of a particular user or to support the economic operation of an existing distribution network. Distributed generation includes micro gas turbine power generation, fuel cell energy storage, and renewable energy sources such as solar and wind power.
Based on grid stability and economic considerations, distributed generation systems store a certain amount of electrical energy to cope with emergencies. Modern energy storage technology has been developed to a certain extent, and has played an important role in distributed power generation, which can improve power quality and maintain grid stability; provide power to users during distributed power generation.
1.4 The role of energy storage technology in electric vehicles
Electric vehicles are powered by electric energy, which can achieve zero emissions and low noise during operation. It is an important means to solve energy and environmental problems. The construction of a strong smart grid will greatly promote the development of electric vehicles, including the establishment of a complete electric vehicle charging and discharging infrastructure network to form a scientific and rational layout of electric vehicle charging and discharging stations. The charging and discharging station infrastructure meets the development of electric vehicle industry and consumers. The need for efficient interaction between electric vehicles and the grid is fully applied.
Compared with traditional fuel vehicles, electric vehicles also have a series of problems such as long charging time, short driving range and high cost of use.
Among them, energy storage technology is the main bottleneck hindering the development of electric vehicle industry. The development of energy storage technology will definitely drive the development of electric vehicle industry.
2. Principles of energy storage technology and common energy storage methods2.1 Principles and characteristics of energy storage technology
An energy storage device composed of energy storage elements and a power grid access device composed of power electronic components become two major parts of the energy storage system. The energy storage device mainly realizes energy storage, release or fast power exchange. The grid access device realizes two-way transmission and conversion of energy between the energy storage device and the power grid, and realizes functions such as power peak shaving, energy optimization, power supply reliability, and power system stability.
The energy storage system has a wide capacity range from tens of kilowatts to several hundred megawatts; the discharge time span is large, from milliseconds to hours; the application range is wide, and the entire power generation, transmission, distribution, and power systems are used; The research and application of power storage technology has just started, it is a new topic, and it is also a hot research field at home and abroad.
2.2 commonly used energy storage methods
At present, energy storage technologies mainly include physical energy storage (such as pumped storage, compressed air energy storage, flywheel energy storage, etc.), chemical energy storage (such as various types of batteries, renewable fuel cells, flow batteries, supercapacitors, etc.) and Electromagnetic energy storage (such as superconducting magnetic energy storage, etc.).
1) The most mature and most commonly used in physical energy storage is pumped storage, which is mainly used for peak shaving, valley filling, frequency modulation, phase modulation, and emergency backup of power systems. Pumped storage can be released from a few hours to a few days, with energy conversion efficiencies ranging from 70% to 85%. The construction period of the pumped storage power station is long and limited by the terrain. When the power station is far away from the power supply area, the transmission loss is large. Compressed air energy storage was implemented as early as 1978, but it was not widely promoted due to terrain and geological conditions. The flywheel energy storage uses the electric motor to drive the flywheel to rotate at a high speed, and converts the electric energy into mechanical energy for storage. When necessary, the flywheel drives the generator to generate electricity. The energy storage of the flywheel is characterized by long life, no pollution, small maintenance, but low energy density, which can be used as a supplement to the battery system.
2) There are many types of chemical energy storage, and the level of technological development and application prospects are also different:
(1) Battery energy storage is currently the most mature and reliable energy storage technology. It can be divided into lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, sodium-sulfur batteries, etc. depending on the chemical substances used. The lead-acid battery has mature technology, can be made into a large-capacity storage system, has low unit cost and system cost, is safe and reliable, and has good reusability. It is also the most practical energy storage system at present, and has been used in small wind power generation and photovoltaic power generation. The system and the small and medium-sized distributed power generation system are widely used, but since lead is a source of heavy metal pollution, lead-acid batteries are not a future development trend. Advanced batteries such as lithium-ion, sodium-sulfur, and nickel-hydrogen batteries are costly, and large-capacity energy storage technologies are still immature. The performance of products cannot meet the requirements of energy storage, and their economics cannot be commercialized.
(2) Large-scale renewable fuel cells have large investment, high price and low cycle conversion efficiency, and it is not suitable as a commercial energy storage system.
(3) The liquid energy storage battery has the advantages of high energy conversion efficiency, low operation and maintenance cost, and is one of the preferred technologies for efficient and large-scale grid-connected power generation and regulation. The liquid energy storage technology has been applied in developed countries such as the United States, Germany, Japan and the United Kingdom, and China is still in the research and development stage.
(4) Supercapacitors are a new type of energy storage device that emerged in the 1980s. Due to the use of special materials to make electrodes and electrolytes, the storage capacity of such capacitors is 20 to 1000 times that of ordinary capacitors, while maintaining the release of conventional capacitors. The advantages of fast energy speed have been continuously applied to power supply occasions such as alpine weather stations and border guard posts.
3) Superconducting magnetic energy storage uses a superconductor to make a coil to store magnetic field energy. It does not need energy conversion when power transmission, and has the advantages of fast response speed, high conversion efficiency, large specific capacity/specific power, etc., which can fully meet the voltage of the transmission and distribution network. Support, power compensation, frequency adjustment, improve grid stability and power delivery requirements. Compared with other energy storage technologies, superconducting magnetic energy storage is still very expensive. In addition to the cost of the superconductor itself, maintaining the system low temperature leads to an increase in the frequency of maintenance and the considerable cost. At present, there are many superconducting magnetic energy storage projects in operation or in the development stage.
The development degree, system scale and application links of various energy storage technologies are shown in Figure 1. The comprehensive comparison of various energy storage technologies is shown in Table 1. In Table 1, the UPS is an uninterruptible power supply.
Due to the large distance span between China's energy center and power load center, the power system has always followed the development direction of large power grids and large motors, operating in accordance with centralized transmission and distribution mode, with the rapid development of renewable energy power generation and social power quality requirements. The continuous improvement of energy storage technology has broad application prospects. The key investment areas of the smart grid recently determined by the State Grid Corporation include a large number of energy storage applications, such as energy storage technology projects in wind power generation and photovoltaic power generation, energy storage technology in power distribution, and electric vehicle charging and discharging technology.
The main application directions of energy storage technology are: 1 Local area network composed of wind power generation and photovoltaic power generation complementary system, used for power supply in remote areas, power supply in factories and office buildings; 2 as uninterruptible power supply and emergency power system in communication system; 3 Wind power generation and On-grid power quality adjustment of photovoltaic power generation system; 4 as a means of large-scale power storage and load peak shaving; 5 electric vehicle energy storage device; (as a large backup power supply for important national departments.
With the continuous advancement of energy storage technology, energy storage technologies with good safety, high efficiency, clean and environmental protection, long life, low cost and high energy density will continue to emerge, which will definitely drive the rapid development of the entire power industry industry chain and create huge Economic and social benefits.
Policy recommendations for promoting the development of large-capacity energy storage industry1) Synchronize energy storage with new energy development. In accordance with the principle of achieving safe operation and efficiency of the entire power system, while planning new energy power generation and power grid transmission lines, corresponding energy storage solutions should be proposed to clarify the scale of energy storage development and construction areas.
2) Implement peak and valley electricity prices and energy storage price policies. Peak and valley electricity prices may vary in different regions, but should try to create more space for the grid to cut peaks and fill the valley and attract energy storage investment.
3) Standardize the technical requirements for new energy generation and grid-connected management. The state should introduce mandatory technical standards for new energy grid-connected and establish a mandatory grid-connected certification and testing system. Implement a short-term forecast reporting system for new energy power generation to improve short-term forecasting capabilities and levels. The power grid company shall receive the electric energy that meets the requirements for network access in full and timely, and selectively receive new energy power generation with poor power quality and large power generation prediction error, and establish a corresponding punishment mechanism.
4) Encourage diversification of investment entities. Under the premise of rationalizing the investment return mechanism and standardizing the technical requirements for network access, all qualified investors such as power producers, power grid companies, customer terminals, and third-party independent energy storage enterprises should be encouraged to invest in energy storage devices.
5) Step up the arrangement of multiple energy storage demonstration projects. Through the implementation of several energy storage demonstration projects, it provides important engineering practice opportunities for energy storage enterprises, and accumulates technical data and operational experience for large-scale application of energy storage technologies in the future. In the demonstration project, it is necessary to consider the performance of various energy storage technologies, and based on the comprehensive evaluation, select the appropriate energy storage technology according to the specific application. Early demonstration projects could be combined with wind power and photovoltaic power generation to explore energy storage technologies for wind power and photovoltaic power generation.
6) Increase R&D investment in large-capacity energy storage technology and encourage diversified development of energy storage technology. The research on energy storage technology should be ahead of demand development. It is not necessary to consider increasing investment when bottlenecks occur. In addition, it is necessary to further increase investment in basic research of energy storage technology, encourage original innovation, and master independent intellectual property rights. Large-scale energy storage technology research and its industrial application should be included in the national science and technology major projects. Since there is no energy storage technology that is fully qualified for various application fields, it is necessary to encourage and support the development of other energy storage technologies while focusing on supporting key technologies such as liquid flow batteries and lithium ion batteries.
V. ConclusionThe application of energy storage technology is an important part of strong smart grid construction, which can effectively realize demand side management, eliminate day and night peaks and valleys, smooth load, improve power equipment operation efficiency, reduce power supply cost, and promote renewable energy. Application, a means to improve grid operation stability, adjust frequency, and compensate for load fluctuations. The construction of smart grid will promote the upgrading of energy storage technology, promote the rapid growth of energy storage demand, especially large-scale energy storage demand, and bring corresponding investment opportunities. With the large number of applications of energy storage technology, changes will be brought about in the design, planning, scheduling and control of traditional power systems.
Energy storage technology is related to national economy and people's livelihood, and has increasingly important economic and social values. The state should study relevant industry standards for energy storage technology as soon as possible, strengthen investment in basic research of energy storage technology, and effectively encourage technological innovation and master independent intellectual property rights; From the initial stage of the development of large-scale energy storage technology, we will pay attention to environmental factors and prevent environmental pollution; give full play to the role of energy storage in energy conservation and emission reduction, and extend the incentive policy for new energy energy to energy storage.
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