The European Commission recently adopted an agreement to further promote the process of transforming the energy system into renewable energy. However, renewable energy power generation is characterized by variability and non-programmability. This has determined that if we want to ensure the safe operation of the electric power system, we must carry out greater upgrading and transformation of the infrastructure, and vigorously develop energy storage systems.

The power grid is actually a complex system, which is composed of generators, lines and loads. They operate at a specific frequency (50/60 Hz) and a standard power supply voltage value. In order to maintain the stability of the system, the energy generated by the generator at a given time must balance the energy demand from the load, so as to establish a balance between production and consumption, or compensate for the difference by using the storage system.

What is a flywheel? The flywheel is a heavy wheel connected to the rotating shaft to smoothly transfer power from the motor to the machine. The inertia of the flywheel will counteract and slow down the speed fluctuation of the engine, and store the excess energy for periodic use. At present, one of the most promising new technologies for storing and regulating power grids is the use of flywheel system, also known as flywheel energy storage (FES). How does it work?

People insert a rotor with great mechanical inertia into a solid cylindrical container and maintain a certain degree of vacuum in the container to reduce noise and aerodynamic friction, which also benefits from the use of magnetic bearings or superconducting materials. The flywheel uses electric energy to accelerate or decelerate, and the stored kinetic energy is exchanged with the power grid through the motor/generator integrated on the rotating shaft. The stored energy depends on the speed and inertia of the flywheel, namely the shape, mass and rotor radius of the flywheel.

Flywheels are classified according to speed, and the speed can reach 100000 rpm. It is believed that the energy storage efficiency of this technology is very high (up to 95%). Because of its fast response time and high flexibility, flywheel technology is very suitable for compensating for short but severe power changes caused by sudden changes in wind and radiation, which will affect the production of solar energy and wind power plants.

In recent years, pilot plants using this technology are under construction. The first large power plant was built for grid frequency regulation, and was put into operation in Stephen Town, New York, in 2011. Then another 20 MW power plant was replicated in Hazler, Pennsylvania. It is believed that with the continuous progress of human science and technology, such green and efficient power systems will become more popular.