1. Mechanical energy storage: mainly including pumped storage, compressed air energy storage, and flywheel energy storage.

(1) Pumped storage: It refers to the process of using excess electricity as a liquid energy medium during low power grid periods to pump water from reservoirs with low terrain to reservoirs with high terrain. During peak load of the power grid, the water from reservoirs with high terrain flows back to the lower reservoir to drive water turbine generators to generate electricity. The efficiency is generally around 75%, commonly known as 4 in and 3 out. It has daily regulation capacity and is used for peak regulation and backup. Shortcomings: Difficulty in location selection, extremely dependent on terrain; The investment cycle is long and the losses are high, including pumping losses and line losses.

(2) Compressed air energy storage: It uses the remaining electricity from the low load of the power system to drive an air compressor by an electric motor, which compresses the air into a sealed, large capacity underground cave that serves as a gas 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 burned, leading it into a gas turbine for power generation. Compressed air storage also has peak shaving function and is suitable for large-scale wind farms, as the mechanical work generated by wind energy can directly drive the compressor to rotate, reducing the intermediate conversion to electricity and improving efficiency. Shortcomings: Low efficiency.

(3) Flywheel energy storage: It uses a high-speed rotating flywheel to store energy in the form of kinetic energy. When energy is needed, the flywheel slows down to release the stored energy. Shortcomings: The energy density is not high enough and the self discharge rate is high. If the charging is stopped, the energy will self exhaust within a few to dozens of hours.