Mechanical energy storage includes pumped water storage, compressed air energy storage, flywheel energy storage, and gravity energy storage.
1. Pumped water storage refers to pumping water from the lower reservoir to the upper reservoir during the low power load period, converting electrical energy into gravitational potential energy and storing it, and releasing the water in the upper reservoir to generate electricity during the peak load period of the power grid. Pumped energy storage is mainly used for peak-shaving and valley-filling, frequency modulation, phase modulation, emergency backup, etc. of the power system.
my country’s pumped water storage technology is currently relatively mature, and its cost is much lower than other energy storage methods. Pumped storage is currently the only energy storage technology that has been applied to power systems on a large scale.
2. Compressed air energy storage refers to the use of electric energy for compressed air during the low load period of the grid, and the air is sealed at high pressure in scrapped mines, subsidence subsea gas storage tanks, caves, expired oil and gas wells or newly built gas storage wells. The compressed air is released during peak periods to drive a steam turbine to generate electricity. Compressed air is mainly used for power peak regulation and system backup.
Compressed air energy storage has the advantages of large scale, long period, and small unit investment. It is a large-scale energy storage technology with great development potential, but it has high requirements for construction and production sites and is dependent on fossil fuels. Experts said that the new compressed air energy storage is still in the demonstration stage.
3. Flywheel energy storage refers to the use of a motor to drive a flywheel to rotate at a high speed, convert electrical energy into mechanical energy and store it, and the flywheel drives a generator to generate electricity when needed. The flywheel system operates in an environment with a high degree of vacuum, and is suitable for power grid frequency regulation and power quality assurance. Flywheel energy storage is still a niche technology in the global and domestic energy storage market.
Flywheel energy storage has several advantages. First, good power characteristics and fast response; second, high efficiency and maintenance-free; third, long service life, generally more than 20 years; fourth, wide application temperature, the working temperature is generally -10 to +40 ℃. In addition, it is environmentally friendly, pollution-free, chemical-free, and there is no pressure to recycle batteries later. However, the cost is high and the energy density is low.
4. The medium of gravity energy storage is mainly water and solid matter. Its working principle is to raise and lower the energy storage medium through the height difference, so as to realize the charging and discharging of the energy storage system. Specifically, the medium is lifted to a high place by electricity to increase its The gravitational potential energy completes the energy storage, and when electricity is needed, the medium falls and uses the gravitational potential energy to convert the kinetic energy into electrical energy.
According to its working principle, it can be seen that solid materials for gravity energy storage require materials with high energy density, such as metals, cement, sand and gravel, etc. In storage and power generation, since no chemical reactions are involved, the overall operation is relatively safe. It also has less impact on the natural environment.