For a long time, the western region of China has a unique advantage in natural resources, and wind, light, heat, gas and other resources have provided strong endorsement support for the economic development of the eastern region of China. However, with the continuous promotion of China’s goal of “carbon peak, carbon neutral”, thermoelectric technology will gradually withdraw from the historical stage, and new energy clean power generation technology will become the backbone of China’s future economic development. How to make full use of natural resources and how to realize the balanced deployment of the national grid will become a new window for the development of new energy technology in China in the future. It can be expected that in the next 5-10 years, energy storage technology will become another hot land for capital pursuit after the development of new energy vehicles.
So what are the current energy storage technologies and principles? Let’s share them briefly.
What is energy storage technology?
The so-called energy storage technology is a technology that converts electric energy into chemical energy, mechanical energy, thermal energy and other forms of energy through technical means, and then reversely converts electric energy to generate electricity when needed.
Northeast people all know that in the past, in the era of material shortage, every household would make some sticky bean bags before winter, freeze them with the help of dry and cold outdoor weather, and then eat them in winter when material shortage. The energy storage power station is to store part of the surplus power when the power is sufficient, and then release it when the power is in urgent need. It can be said that the energy storage power station is the sticky bean bag of the national grid system.
Why should we store energy?
Energy storage technology has been developed with the continuous progress of power generation technology. Due to the characteristics of the difficulty in storage of electricity, at the low point of power consumption, a part of excess electricity that cannot be used will be lost in the form of heat. Especially with the rise of clean power generation technologies such as photovoltaic power generation and wind power generation, in order to make full use of natural resources to obtain more electricity, power generation will be carried out with maximum efficiency when there is sufficient sunlight and strong wind in the daytime, but at this time, it may be at the peak of power consumption, so even if a lot of electricity is generated at this time, it is not used in time, When the power consumption peak, the power may be insufficient due to insufficient power generation. The energy storage technology can solve the “absorption” problem well. It can be stored when there is more electricity and released when there is less electricity, so as to balance the power allocation and frequency modulation of the power grid, which is important for stabilizing the balance between supply and demand of the power grid and the national power security.
What are the energy storage technologies?
According to the classification of energy storage technology, it can be divided into physical energy storage and chemical energy storage. At present, pumped storage, flywheel energy storage, molten salt heat storage, superconducting electromagnetic energy storage, electrochemical energy storage and hydrogen energy storage are widely used. With the continuous development of energy storage technology, new energy storage technologies will be born in the future. The following is a brief introduction to the widely used energy storage technology.
Pumped storage: It is a kind of energy storage method that converts electric energy into potential energy of water. According to the source classification of power generation water source, it can be divided into two types: mixed type and pure pumping type. The mixed type is that the water source of the upstream reservoir is not only pumped from the downstream reservoir, but also continuously supplemented by the natural water source; The water source of the pure pumping upstream reservoir is completely obtained from the downstream reservoir. At present, the world’s largest Fengning pumped storage power station in Hebei is a pure pumping storage power station. China’s pumped-storage power stations started relatively late. The first two small hybrid pumped-storage power stations, Pingshan in Hebei and Miyun in Beijing, were built in 1968 and 1973 respectively, with installed capacity of only 11MW and 22MW. At present, about 20 pumped-storage power stations have been built and are under construction in China (data from Baidu), 247 pumped-storage storage projects proposed in the Medium and Long-term Development Plan for Pumped Storage (2021-2035), with a total installed capacity of about 305 million kilowatts. The construction technology of pumped storage power stations is relatively mature, but there are certain requirements for geographical conditions, 60% of which are distributed in North China and East China.
Compressed air energy storage: It is an energy storage method that converts electric energy into compressed air internal energy. Compressed air energy storage mainly uses the remaining electric compressed air at the low load of the power grid, and stores it in the high-pressure sealing facilities, and releases it at the peak of power consumption to drive the modified gas turbine to generate electricity. Its development is later than that of pumped storage technology. In 1978, Germany built the world’s first compressed air energy storage power station. At present, the first commercial power station for compressed air energy storage in China is the 10 MW compressed air energy storage project in Feicheng, Tai’an, Shandong in 2021, which takes full advantage of the natural advantages of good airtightness and high stability of underground salt caverns in the surrounding area of Feicheng, Tai’an. Therefore, compressed air energy storage has higher requirements for geographical environment, and its applicability is limited. However, with the development of thermal insulation materials and sealed tank technology, the ground air energy storage technology is constantly developing. Due to the low cost of construction and maintenance, it is another energy storage technology that may be vigorously developed after the pumped storage power station.
Molten salt heat storage: It is an energy storage method that converts electric energy into heat energy. Molten salt is composed of 60% sodium nitrate and 40% potassium nitrate. Its principle is to use phase change technology to store and release energy by absorbing and releasing heat during phase change. It is generally complementary to photovoltaic technology, known as “photothermal” power generation technology. During the day, solar energy is used to heat and melt the salt, and the solar energy is stored in the form of heat. At night, when electricity is needed, liquid molten salt is extracted to release heat energy for power generation. In 2016, China’s first large-scale molten salt energy storage tower photothermal power station was put into operation in Qinghai, marking that China officially has a complete set of technologies of photothermal+molten salt energy storage. This technology is a very attractive technology for the vast, sunny and long time western region.
Flywheel energy storage: It is an energy storage method that converts electric energy into kinetic energy. During energy storage, the external electric energy is transformed by the electric converter and drives the motor to run. The motor drives the flywheel rotor to accelerate rotation until it reaches a set speed. The flywheel stores the energy in the form of kinetic energy. After receiving the energy release signal, the high-speed rotating flywheel drives the motor to generate electricity, release the kinetic energy in the form of electric energy, and output the current and voltage applicable to the load through the power converter to complete the energy release process from mechanical kinetic energy to electric energy conversion. In the process of releasing energy, the rotational speed of the flywheel decreases continuously. The whole flywheel energy storage system realizes the input, storage and output of electric energy. However, the energy density of flywheel energy storage is low, and it is difficult to set it for different scenarios. In the future, it is mainly applicable to market segments, and it is unlikely to be used as a large area of power reserve.
Superconducting energy storage: It is a kind of energy storage method that converts electric energy into electromagnetic energy or mechanical energy. At present, there are two kinds of superconducting energy storage: superconducting electromagnetic energy storage and superconducting flywheel energy storage. Superconducting electromagnetic energy storage is to use superconducting coils to convert electric energy into electromagnetic energy for storage, while superconducting flywheel energy storage is to use superconducting magnetic bearings to realize the rotation of flywheel without energy loss by using superconducting friction-free characteristics, and to convert electric energy into kinetic energy of flywheel for storage. On April 19, 2011, the world’s first distributor-level superconducting substation, developed by the Institute of Electrical Engineering of the Chinese Academy of Sciences, was put into the actual distribution network for engineering demonstration operation in the National High-tech Industrial Development Zone of Baiyin City, Gansu Province. This is also the only superconducting substation in the world that has been put into demonstration operation at present. The characteristics of low loss and fast response of superconducting materials are fully utilized. Its advantages are high energy storage density, small loss, fast reaction and high power. However, at present, the research and development, construction and maintenance costs of high-temperature superconducting materials are relatively high. Thanks to China’s leading position in the research of superconducting materials in the world, the superconducting electromagnetic energy storage technology may make a major breakthrough in the future.
Electrochemical energy storage: It is a kind of energy storage method that converts electrical energy into chemical energy. At present, electrochemical energy storage is mainly through the construction of “large charging bank”, which will charge the battery at the low point of power consumption, and release the electric energy in the battery at the high point of power consumption to relieve the load pressure of the power grid. In 2016, China started construction of the first 800MW large-scale chemical energy storage power station in Xigang District, Dalian, with a total investment of 3.8 billion yuan, and will be completed in 2021. The project is currently the largest chemical energy storage power station in the world. With the popularization of pure electric vehicles, the recycling of waste batteries is an urgent issue to be solved. At present, many enterprises have begun to try to apply battery energy storage technology, which is also a very ideal technology for the realization of small-scale pure electric vehicle energy supplement technology in the future.
Hydrogen energy storage: It is an energy storage method that converts electric energy into secondary energy. Its principle is a technology that converts electric energy into chemical energy storage of hydrogen by electrolysis of water. This is the “green hydrogen” hydrogen production technology developed after the gray hydrogen and blue hydrogen technology, which uses green clean energy to realize the secondary energy conversion. With the development of hydrogen energy vehicles, hydrogen energy storage technology can not only solve the problem of vehicle power fuel, but also balance the power demand. This is an important technical route to solve the source of automobile power fuel in the future.
With the continuous development of energy storage technology, fluid energy storage, supercapacitor energy storage and other technologies will gradually develop in the future. But it is all to achieve the balance of high and low loads of the power grid by means of “peak shaving and valley filling”. Due to the advantages and disadvantages of various energy storage technologies and different scenarios, various energy storage technologies should be developed based on geographical advantages and return on investment to achieve balanced development of economic and social benefits.
