Energy storage technologies are mainly divided into electrical storage and thermal storage. Currently, energy storage methods are mainly classified into three categories: mechanical energy storage, electromagnetic energy storage, and electrochemical energy storage. Among them, mechanical energy storage primarily includes pumped hydro storage, compressed air storage, and flywheel energy storage.
1. Pumped storage
Pumped storage is a system that uses excess electricity as a liquid energy medium to pump water from a low-lying reservoir to a high-lying reservoir during off-peak hours. During peak load periods, the water in the high-lying reservoir flows back to the lower reservoir to drive turbine generators to generate electricity. The power output is typically around 75%, commonly known as "4 in, 3 out," and it has daily dispatch capabilities for peak shaving and backup.
Disadvantages: Difficult site selection and reliance on terrain; long investment cycle and high losses, including pumped storage losses and line losses; currently constrained by my country's electricity pricing policy, with over 80% of pumped storage power remaining idle last year. In August of last year, the National Development and Reform Commission issued a policy on pumped storage electricity pricing, which may improve things in the future, but it is certainly not the trend for energy storage development.
2. Compressed Air Energy Storage (CAES)
Compressed air energy storage utilizes surplus electricity generated during off-peak hours in the power system. An electric motor drives an air compressor to force air into a large-capacity, sealed underground storage chamber. When the system's power generation is insufficient, the compressed air is mixed with oil or natural gas through a heat exchanger and then burned, with the mixture being fed into a gas turbine to generate electricity. Research in this area is more extensive and the technology is more mature abroad. my country's initial research started somewhat later, but it seems that Academician Lu Qiang has conducted considerable research in this field.
Compressed air storage also has peak-shaving function and is suitable for large-scale wind farms because the mechanical function generated by wind energy can directly drive the compressor to rotate, reducing the intermediate conversion to electricity and thus improving power.
Disadvantages: A major drawback is the relatively low power output. This is because the temperature increases when air is compressed and decreases as it expands. Some energy is lost as heat during compression, requiring reheating before expansion. Natural gas is typically used as the heat source, leading to reduced energy storage capacity. Other notable drawbacks include the need for large-scale gas storage facilities, specific geological conditions, and reliance on burning fossil fuels.
3. Flywheel energy storage:
Flywheel energy storage uses a high-speed rotating flywheel to store energy as kinetic energy. When energy is needed, the flywheel slows down and releases the stored energy. China has largely mastered the individual technologies involved in flywheel energy storage (but lags behind foreign countries by more than 10 years). The difficulty lies in developing new products with different functions for different applications. Therefore, while flywheel energy storage is a high-tech product, it lacks initial innovation, making it difficult to obtain national research funding.
Disadvantages: Insufficient energy density and high self-discharge rate; if charging is interrupted, the energy will be depleted within a few to tens of hours. Suitable only for certain niche markets, such as high-quality uninterruptible power supplies.
