Rotor design for high-speed flywheel energy storage systems

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  • Devices employing the concept of kinetic energy storage date back to ancient times. Pottery wheels and spinning wheels are early examples of systems employing kinetic energy storage in a rotating mass. With the advent of modern machinery, flywheels became commonplace as steam engines and internal combustion engines require smoothing of the fluctuating torque that is produced by the reciprocating motion of the pistons of such machines. More recently, flywheel systems were developed as true energy storage devices, which are also known as mechanical or electromechanical batteries. A remarkable example of such a system was the sole power source of the ’Gyrobus’ - a city bus that was developed by the Maschinenfabrik Oerlikon in Switzerland in the 1930’s, see Motor Trend (1952). This vehicle contained a rotating flywheel that was connected to an electrical machine. At regular bus stops, power from electrified charging stations was used to accelerate the flywheel, thus converting electrical energy to mechanical energy stored in the flywheel. When traveling between bus stops, the electrical machine gradually decelerated the flywheel and thus converted mechanical energy back to electricity, which was used to power the electrical motor driving the bus. The disk-shaped flywheel rotor was made of steel, had a mass of about 1.5 metric tons and reached a maximum angular velocity of 314 rad/s or 3000 rounds per minute (rpm). In regular operation, deceleration of the flywheel was limited to about half of the maximum disk speed. The amount of energy thus made available allowed the Girobus to travel for a distance of up to 6 km in regular traffic. Contemporary flywheel energy storage systems, or FES systems, are frequently found in high-technology applications. Such systems rely on advanced high-strength materials as flywheels usually operate at speeds exceeding 10,000 rpm. Vacuum enclosures and magnetic bearing systems are frequently employed to minimize energy losses due to friction. Only through the use of advanced technology have FES systems become commercially viable for a range of applications, causing FES research and development to be an active and rapidly evolving field.

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    Attribution-NonCommercial-ShareAlike 4.0 International
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    • Krack, Malte., Secanell, Marc., Mertiny, Pierre., & Carbone, R. (2011). Rotor design for high-speed flywheel energy storage systems. In chapter 3 from Energy Storage in the Emerging Era of Smart Grids (pp. 41-58). In Tech.
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