1. Principles and characteristics of energy storage technology
The energy storage device composed of energy storage elements and the grid access device composed of power electronic devices have become the two major parts of the energy storage system. Energy storage devices are important to realize energy storage, release or rapid power exchange. The grid access device realizes the two-way transfer and conversion of energy between the energy storage device and the grid, and realizes functions such as power peak shaving, energy optimization, and improvement of power supply reliability and power system stability.
The capacity range of the energy storage system is relatively wide, from tens of kilowatts to hundreds of megawatts; the discharge time span is large, from milliseconds to hours; the application range is wide, and it runs through the entire power generation, transmission, distribution, and power consumption system; large-scale The research and application of power storage technology has just started. It is a brand-new subject and a hot area of research at home and abroad.
2. Commonly used energy storage methods
At present, energy storage technologies mainly include physical energy storage (such as pumped water storage, compressed air energy storage, flywheel energy storage, etc.), chemical energy storage (such as various types of batteries, renewable fuel power batteries, flow batteries, super capacitors, etc.) And electromagnetic energy storage (such as superconducting magnetic energy storage, etc.).
1) The most mature and widely used physical energy storage is pumped storage, which is mainly used for peak regulation, valley filling, frequency modulation, phase modulation, emergency backup, etc. of the power system. The release time of pumped storage can range from a few hours to a few days, and its energy conversion efficiency is between 70% and 85%. The construction period of pumped-storage power stations is long and restricted by topography. When the power station is far away from the power consumption area, the transmission loss is relatively large. Compressed air energy storage has been applied as early as 1978, but due to the constraints of topography and geological conditions, it has not been widely promoted. Flywheel energy storage uses an electric motor to drive the flywheel to rotate at high speed, convert electrical energy into mechanical energy and store it, and the flywheel drives a generator to generate electricity when needed. Flywheel energy storage is characterized by long life, no pollution, low 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. According to the different chemical substances used, it can be divided into lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, sodium-sulfur batteries, etc. Lead-acid battery has mature technology, can be made into a large-capacity storage system, low unit energy cost and system cost, safety, reliability, and good reusability. It is also the most practical energy storage system at present. It has been used in small wind power generation and photovoltaic power generation. It has been widely used in systems and small and medium-sized distributed power generation systems, but because lead is a source of heavy metal pollution, lead-acid batteries are not the future development trend. Advanced storage batteries such as lithium-ion, sodium-sulfur, and nickel-metal hydride batteries have high costs, and large-capacity energy storage technologies are not yet mature. The performance of the products currently cannot meet the requirements of energy storage, and its economics cannot be commercialized.
(2) Large-scale renewable fuel power cells have large investment, high prices, and low cycle conversion efficiency, and are currently not suitable for commercial energy storage systems.
(3) Liquid flow energy storage battery has the advantages of high energy conversion efficiency and low operation and maintenance costs. It is one of the technologies for high-efficiency, large-scale grid-connected power generation, energy storage and regulation. Liquid flow energy storage technology has been used for demonstration in developed countries such as the United States, Germany, Japan, and the United Kingdom. my country 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 this type of capacitor is 20 to 1,000 times that of ordinary capacitors, while maintaining the release of traditional capacitors. The advantages of fast energy speed have been continuously applied to power supply occasions such as high mountain weather stations and border posts.
3) Superconducting magnetic energy storage utilizes superconductors to make coils 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 fully meet the voltage of transmission and distribution network Support, power compensation, frequency adjustment, improve grid stability and power transmission capacity 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 low temperature of the system leads to an increase in the frequency of maintenance and the resulting costs are also considerable. At present, there are many superconducting magnetic energy storage projects in operation or in the development stage around the world.
The comparison of the development level, system scale and application links of various energy storage technologies is shown in Figure 1. The comprehensive comparison of various energy storage technologies is shown in Table 1. In Table 1, UPS is an uninterruptible power supply.
The development prospects of the energy storage industry
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 motors, and operated in accordance with the centralized transmission and distribution mode. With the rapid development of renewable energy power generation and the society’s requirements for power quality With the continuous improvement of energy storage technology, the application prospect of energy storage technology is broad. The key investment areas for smart grids recently identified by the State Grid Corporation of China include a large number of energy storage applications, such as the application of energy storage technology projects in wind power and photovoltaic power generation in the power generation field, energy storage technology in the power distribution field, and electric vehicle charging and discharging technology.
The important application directions of energy storage technology are: ①The local area network composed of wind power and photovoltaic power generation complementary systems is used for power supply in remote areas, factories and office buildings; ②As an uninterruptible power supply and emergency power system in the communication system; ③Wind power and Grid-connected power quality adjustment of photovoltaic power generation systems; ④As a means of large-scale power storage and load peak shaving; ⑤Electric vehicle energy storage devices; (As a large-scale backup power supply for important national departments, etc.).
With the continuous advancement of energy storage technology, energy storage technologies with good safety, high efficiency, clean and environmentally friendly, long life, low cost, and high energy density will continue to emerge, which will surely drive the rapid development of the entire power industry industry chain and create huge Economic and social benefits.
Policy recommendations to promote the development of large-capacity energy storage industry
1) Simultaneous planning of energy storage and new energy development. In accordance with the principle of achieving safe operation and optimal efficiency of the entire power system, while planning new energy generation and grid transmission lines, corresponding energy storage solutions should be proposed, and the scale of energy storage development and construction areas should be clarified.
2) Implementation of peak and valley electricity price and energy storage electricity price policies. Peak-to-valley electricity prices may vary in different regions, but we should try our best to create more room for power grids to cut peaks and fill valleys and attract energy storage investment.
3) Standardize new energy power generation technical requirements and grid connection management. The state should issue mandatory technical standards related to grid-connected new energy, and establish a mandatory grid-connected certification and testing system. Implement the short-term forecasting and reporting system of new energy power generation output to improve the short-term forecasting ability and level. Grid companies should receive the power that meets the grid access requirements in time and in full, and can selectively receive new energy power generation with poor power quality and large power generation forecast errors, and establish a corresponding penalty mechanism.
4) Encourage diversification of investment entities. Under the premise of rationalizing the investment return mechanism and standardizing the technical requirements for network access, any qualified investors such as power generators, grid companies, user terminals, and third-party independent energy storage companies should be encouraged to invest in the construction of energy storage devices.
5) Step up arrangements for multiple energy storage demonstration projects. Through the implementation of several energy storage demonstration projects, it provides energy storage companies with important engineering practice opportunities, and accumulates technical data and operational experience for the large-scale application of energy storage technology in the future. In the demonstration project, it is necessary to consider the performance of various energy storage technologies, and on the basis of comprehensive evaluation, select appropriate energy storage technologies according to specific uses. Early demonstration projects can be combined with wind power and photovoltaic power generation to explore energy storage technologies applied to wind power and photovoltaic power generation.
6) Increase investment in research and development of large-capacity energy storage technology and encourage the diversified development of energy storage technology. The research of energy storage technology should be ahead of the development of demand. It is not necessary to wait for the bottleneck to consider increasing investment. 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. The research on large-scale energy storage technology and its industrial application should be included in major national science and technology projects. Since there is no energy storage technology fully qualified for the requirements of various application fields, while focusing on supporting key technologies such as flow batteries and lithium-ion batteries, the development of other energy storage technologies should also be encouraged and supported.
