I. Thermal Energy Storage Technology
Thermal energy storage involves storing excess heat that is not needed for a certain period of time through some method, and then retrieving and using it when needed. It includes three types: sensible heat storage technology, latent heat storage technology, and chemical reaction thermal energy storage technology.
1. Sensible heat energy storage technology
Sensible thermal energy storage technology stores heat energy by heating the storage medium to increase its temperature. Commonly used sensible thermal energy storage materials include water, soil, and rock. Under the same temperature change conditions, and neglecting heat loss, water has the highest heat storage capacity per unit volume, followed by soil, and then rock. Many countries around the world have already tested and applied these thermal energy storage materials. Currently, this is a relatively mature, efficient, and low-cost energy storage method.
2. Latent heat energy storage technology
Latent heat storage technology utilizes the heat of fusion generated during the phase transition between the liquid and solid phases of the storage medium to store thermal energy. Practically used latent heat storage media include sodium sulfate decahydrate (chemical formula Na₂SO₄·10H₂O), sodium thiosulfate pentahydrate (chemical formula Na₂SO₄·5H₂O), and calcium chloride hexahydrate (chemical formula CaCl₂·6H₂O), among others.
3. Chemical energy storage technology
Chemical energy storage technology utilizes the decomposition of chemical substances to store energy separately. When the decomposed substances recombine, the stored heat energy is released. This can be achieved using three technologies: reversible decomposition reactions, reversible organic reactions, and hydride chemical reactions. Among these, hydride chemical reaction technology has the greatest development potential and is being studied extensively both domestically and internationally. A breakthrough success in this area would provide a promising solution to the energy shortage problem.
II. Energy Storage Technology
There are three main types of energy storage technologies that have been applied in industry: hydroelectric energy storage, compressed air energy storage, and flywheel energy storage.
1. Hydropower storage technology
Hydropower storage technology is the oldest, most mature, and largest commercially available technology, with approximately 500 hydropower storage power plants worldwide, including 35 with a capacity exceeding 1000MW. A typical hydropower storage system consists of two large reservoirs, one located at a lower elevation and the other at a higher elevation. During off-peak electricity demand, water is moved from the lower reservoir to the higher one for storage. When electricity is needed, the potential energy of the water flow in the higher reservoir powers a hydroelectric generator.
2. Compressed air energy storage
Compressed air energy storage involves pressurizing and delivering air to underground salt mines, abandoned stone mines, and underground aquifers during off-peak electricity demand periods. When the electricity load is high, the compressed air can be burned with fuel to produce high-temperature, high-pressure gas, which drives a gas turbine to generate electricity. The capacity of the units used in this technology has reached several hundred megawatts. For example, the 290MW Fendolf power plant in Germany was put into operation in 1980.
3. Flywheel energy storage power generation technology
Flywheel energy storage power generation technology is a novel technology that connects to the power grid to convert electrical energy into electrical energy. A flywheel energy storage power generation system mainly consists of a motor, flywheel, and power electronic converter. The basic principle of flywheel energy storage is to convert electrical energy in the power system into the kinetic energy of the flywheel's motion when there is a power surplus. When the power system is short of electrical energy, the kinetic energy of the flywheel's motion is then converted back into electrical energy for power users.
