Optimization of Flywheel Geometry for Mechanical Energy Storage to Mitigate Renewable Power Variability

Overview

Flywheel Energy Storage Systems (FESS) are mechanical systems that are used to conserve energy through rotational kinetic energy and release it quickly when needed, making them useful for stabilizing power grids as renewable energy sources continue to expand. This study investigated how flywheel diameter and mass distribution affect energy storage and electrical output. Cast-iron flywheels were spun to a constant speed of 500 RPM before the motor was disengaged, allowing the system to spin down while transferring energy through a permanent magnet generator. Two flywheel diameters, 12 inches and 18 inches, were tested to see how size influences rotational inertia and stored energy. Mass distribution was also tested by placing six shaft collars near the center of the wheel and near the rim while keeping the total added mass constant. Voltage and current with respect to time were recorded at 0.5-second intervals to calculate electrical energy output and efficiency, and four trials were held for each condition to ensure reliability. The results showed that larger flywheel diameters and mass positioned farther from the axis increased the moment of inertia, allowing the system to maintain its rotation and produce greater electrical output than the smaller diameter. Out of the four trials, the 12-inch flywheel had an average efficiency of 5.73 %, while the 18-inch wheel reached 7.01 %, showing that increasing diameter improved energy retention. Adding six shaft collars near the center of the 12-inch wheel increased its moment of inertia, giving an average efficiency of 5.85%. Moving the same collars to the rim further increased the moment of inertia, producing the highest efficiency of 6.43%. Overall, these results indicate that both diameter and mass distribution strongly influence rotational energy retention and energy output.

Competition history

• CSEF 2026 Applied Mechanics (Senior Division) · Entry S-02-30

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