As global energy systems transition toward high shares of renewable energy

maintaining frequency stability becomes increasingly challenging in the case of the reduced inertia and dispatchability of inverter-based resources. Power generation

including renewable energy technologies as well as thermal power generation

continues to serve a vital role in frequency regulation of power grids but confronts accelerating operational issues

especially when tackling frequent

rapid cycling. Flywheels with their fast response

high power density

long cycle life

and minimal environmental drawbacks

have emerged as promising auxiliary resources for enhancing flexibility in frequency regulation challenges. This paper presents a comprehensive review of flywheel technology development and its limitations

followed by an introduction to the diverse types of grid-scale high-power flywheel energy storage systems. Overviews of the flywheel-assisted power grid paradigm

focusing on advanced flywheel technologies

coordinated control strategies

and economic optimizations in electrical trading markets

are also summarized. The electricity trading market mechanisms

including ancillary service reforms and capacity payments

which reshape power grid balancing by leveraging the role of fast-response storage

are further investigated and discussed. Finally

practical pilot implementations are examined in regions such as Shanxi and Ningxia

China

and Bacon

the United States

demonstrating the efficacy of the independent Flywheel Energy Storage System (FESS) and assisted power generation. This insight expands the research landscape and provides new directions including the interoperability of FESS with low-inertia grids

comprehensive lifecycle assessment

integration within hybrid storage topologies

and the design of investment incentives to promote large-scale adoption.