Analysis and design of the capacity and efficiency of a flywheel energy storage system

In this paper, the energy and power characteristics of a flywheel energy storage system are analyzed. Current flywheel energy storage systems could store approximately 0.5-100 kW·h energy and discharge at a rate of 2-3000 kW. Here a design of a 100kW·h flywheel is proposed. By using a low speed steel flywheel rotor with a stress limit of 800 MPa, the energy density could reach 13-18W·h/kg. With such a stress level, however, the size of the flywheel could reach the meter scale, making it difficult to manufacture. To overcome such a challenge, a multi-disc axial connection structure design was proposed. The high-speed composite flywheel rotor was designed with 3 or 4 thin cylinders made from winding fber reinforced composite considering the radial stress optimization. Stress analyses indicated that both the 3-layer flywheel at a speed of 9000 r/min and the 4-layer flywheel at a speed of 15000 r/min would meet the structural strength requirements with an energy density at 50-70 W·h/kg.