Abstract - This study gives a critical review of flywheel energy storage systems and their feasibility in various applications. Where is. . Flywheel is a rotating mechanical device used to store kinetic energy. With daily ridership exceeding 4 million passengers, the system's power consumption rivals small cities. Last month's 12-hour service disruption due to grid instability?. Application areas of flywheel technology will be discussed in this review paper in fields such as electric vehicles, storage systems for solar and wind generation as well as in uninterrupted power supply systems. Flywheels are an excellent mechanism of energy storage for a range of reasons, starting with their high efficiency level of 90% and estimated long lifespan.