This paper presents a comprehensive analytical framework for investigating loss mechanisms and thermal behavior in high-speed magnetic field-modulated motors for flywheel energy storage systems. . dby losses in the flywheel rotor part of a flywheel energy storage system (FESS). Although these losses are typically small in a well-designed system, the energy losses can become significant due to the continuous operation of the flywheel over time. Through systematic classification of electromagnetic, mechanical, and additional losses, we reveal that. . Understanding the intricacies of energy losses in flywheel energy storage systems reveals several critical factors impacting efficiency. The energy loss in flywheels is primarily attributed to friction al losses, 2. Other significant losses occur due to air resistance, 3. Electrical conversion. . There is noticeable progress in FESS, especially in utility, large-scale deployment for the electrical grid, and renewable energy applications. This paper gives a review of the recent developments in FESS technologies. Due to the highly interdisciplinary nature of FESSs, we survey different design. . Flywheel energy storage (FES) works by spinning a rotor (flywheel) and maintaining the energy in the system as rotational energy. Standby loss typically ranges from 1% to 5% of the stored energy capacity per hour. This figure varies based on multiple factors such as flywheel design, materials, and ambient. .