Unlike chemical batteries, flywheels are capable of rapid charge and discharge without degradation and hence are particularly suited for applications requiring quick response times, such as frequency regulation. Frequency is one of the most significant challenge factors in. . Flywheels have been used to store energy in rotation for centuries. tied to operate at the grid frequency. FESSs have high energy density, durability, and can be cycled frequently without. . Flywheel energy storage systems have recently been found to be one of the firmest and most reliable solutions to stabilize power grids, primarily in today's fast-changing energy world.