In the analysis of energy storage processes, the part of the object or spatial area that is delineated to determine the object of study is called the energy storage system. It includes energy and matter input and output, energy conversion, and storage devices. Energy storage systems often involve multiple energies, multiple devices, multiple substances, and multiple processes and are complex energy systems that change with time, requiring several indicators to describe their performance. Commonly used evaluation indicators are energy storage density, energy storage power, energy storage efficiency, as well as the price of energy storage, the impact on the environment, etc.
Since the energy required by people is highly temporal and spatial, To use vitality rationally and improve the virtue of spirit, a device is needed to collect and store the excess energy that is temporarily not used for some time in some way. It can be withdrawn at the peak of use or transported to a place where vitality is in shortage and used again. This method is called energy storage.
The first task of an energy storage system is to overcome temporal or local differences between energy supply and demand. Such discrepancies arise in two ways. One is caused by a sudden change in energy demand, that is, there is a peak load problem. The use of energy storage methods can act as a regulator or buffer when the rate of load change increases Since the investment cost of an energy storage system is relatively lower than building a peak load plant. Even though the energy storage device will have storage losses, it can still reduce fuel costs because the stored energy is excess energy from the plant or new energy sources. The other is caused by primary energy sources and energy conversion devices and the like, then the task of the energy storage system (device) is to equalize energy production, that is, not only to cut the peak of energy output but also to fill the trough of output (i.e., fill the valley).
For example, in solar thermal systems, energy storage is required. When the heat flow leaves the collector and enters the warehouse, it then passes through the heat energy converter to supply the heat engine. During periods when there is no sunlight, the cold fluid passes directly through the storage, extracts the stored heat, and carries it to the heat engine to work.
Therefore, the energy storage system can store excess heat, kinetic energy, electrical energy, potential energy, chemical energy, etc., and change the output capacity of energy, output location, output time, etc.
Energy storage mainly includes thermal, kinetic, electrical, electromagnetic, chemical, and other energy storage. For energy storage technology, see Table 1.5. and air-conditioning energy-saving fields.
(1) Thermal Energy Storage Technology
Thermal energy storage is to store the excess heat that is not needed casually for some time by some method and then extract it for use when needed. It includes three kinds of thermal energy storage technologies: sensible thermal energy storage technology, latent thermal energy storage technology, and chemical reaction thermal energy storage technology, and the comparison of the three kinds of thermal energy storage is shown in Table 1.6.
Apparent thermal energy storage technology is to grow the temperature of the energy storage medium by heating it and the thermal energy stored in it. Commonly used sensible thermal energy storage materials are water, soil, and rock. Under the same conditions of temperature change, if the heat loss is not considered, then the unit volume of heat storage water is the largest, followed by soil and rock is the smallest. Many countries around the world have tested and applied these thermal storage materials. For the time being, this is a more mature technology, higher efficiency, and low-cost energy storage method.
Latent heat energy storage technology is the use of an energy storage medium between the liquid phase and the solid phase of the phase change when the heat of melting will be stored in the thermal energy. In the actual application of latent heat storage medium, there is sodium sulfate decahydrate (the chemical formula is Na2S04·10H20), sodium thiosulfate pentahydrate (the chemical formula is Na2S04·5H20), and calcium chloride hexahydrate (the chemical formula is CaCl2·6H20) and so on. The technology is characterized by energy storage at low temperatures, has a high energy storage density, and can take out heat at an inevitable phase change temperature. But the energy storage medium is expensive and easy to corrode. Some media may also produce decomposition reactions, and the storage device is too more complex than the sensible heat type, which is technically difficult.
Chemical energy storage technology uses energy to store energy separately after decomposing chemical substances, and the stored thermal energy can be released when the decomposed substances are recombined. It can be realized by using three technologies: reversible decomposition reaction, organic reversible reaction, and hydride chemical reaction, among which hydride chemical reaction technology is the most promising and is being studied in depth both at home and abroad, if it can achieve breakthrough success, it will provide a great way to solve the problem of energy shortage.
(2)Electric energy storage technology
There are three main types of electric energy storage technologies that have been used in industry, namely, hydraulic energy storage technology, compressed air energy storage technology, and flywheel energy storage technology. Hydraulic energy storage technology is the oldest, the most mature technology, and the maximal equipment capacity of commercial technology. The world has about 500 hydraulic energy storage power stations, of which the ability to more than 1000MW has 35. Hydro energy storage systems generally have two large storage reservoirs, one in a lower position and the other in a higher lift position. During the flat peak period of electricity consumption, water is sent from the reservoir at the lower location to the storage reservoir at the upper location to be stored. When electricity is needed, the potential energy of the water flow in the high reservoir can be used to drive the hydropower machine to generate electricity.
Compressed air energy storage is the pressurized delivery of air to underground salt mines, abandoned quarries, underground water reservoirs, etc. During low peak periods of electricity consumption. When t he loads of electricity consumption is high, compressed air can be burned with fuel to produce high-temperature, high-pressure gas to drive the gas turbine to do work to generate electricity. The capacity of the applied unit equipment has reached several hundred megawatts. For example, the German Fendorff power station with an installed capacity of 290 MW was put into operation in 1980.
Flywheel energy storage and generation technology is a new technology, which is connected to the power grid to realize the conversion of electrical energy. The system mainly consists of motors, flywheels, power electronic converters, and other equipment. The basic principle of flywheel energy storage is to convert the electric energy in the power system into kinetic energy of flywheel movement under the condition of electric affluence. And when the power system power is insufficient, then the kinetic energy of flywheel motion is converted into electricity for power users. Compared with other energy storage technologies, flywheel energy storage technology has the advantages of high efficiency (80%-90%), low cost, no pollution, rapid energy storage, reliable technology, and so on. which has attracted the attention of researchers in Japan, the United States, and Germany. For example, Japan Okinawa Electric Power Company developed a 210MJ flywheel energy storage system; In 1996, Germany developed a superconducting magnetic levitation energy storage flywheel energy storage power station with an energy storage capacity of 5MW·h/100MW·h, and the system efficiency reached 96%.
