1、 Mechanical energy storage

The application forms of mechanical energy storage only include pumped storage, compressed air storage, and flywheel energy storage.

1. Pumped storage energy

When the power grid is at a low point, excess electricity is used to pump water as a liquid energy medium from low elevation reservoirs to high elevation reservoirs. During peak load of the power grid, water from high elevation reservoirs flows back to the lower reservoir to drive the turbine generator to generate electricity.

At present, the world average proportion of pumped storage units in a country's total installed capacity is about 3%. As of the end of 2012, the total capacity of energy storage devices worldwide was 128GW, of which 127GW was pumped storage, accounting for 99%.

As of the end of 2016, the capacity of pumped storage power stations in China was 50.325 million kilowatts, with an operating capacity of 23.385 million kilowatts and an ongoing capacity of 26.94 million kilowatts, accounting for approximately 3% of the total installed capacity of 1.65 billion kilowatts in the country. (Another 8 buildings under construction with a capacity of 8.94 million kilowatts)

2. Flywheel energy storage

In a flywheel energy storage system, electrical energy is used to accelerate a rotor placed inside a vacuum casing, which is a massive cylinder made of solid material (up to tens of thousands of revolutions per minute), thereby storing electrical energy in the form of kinetic energy (utilizing the inertia capacity stored by the large rotor).

Flywheel energy storage is commonly used in industry and UPS, suitable for frequency regulation in power distribution systems. It can be used as a UPS without a battery to quickly transfer power in case of power supply failure, maintain short-term frequency stability of small systems, and ensure power quality (power outage, voltage fluctuations, etc.).

It has just started to be installed and used in power distribution systems in China. The Power Electronics Research Institute of the Chinese Academy of Electrical Sciences has installed a flywheel energy storage system with a capacity of 250kVA and magnetic levitation bearings for Beijing 306 Hospital, which can operate for 15 seconds. It was put into operation in 2008.