Frequency control in islanded microgrids is expected to become increasingly critical as renewable energy sources (RES) increase

due to the decarbonisation target. The power electronic inverters that interface RES with the electrical grid inherently have low

inertia and limited short-circuit current, posing significant challenges to the operation of an isolated electric power system. To

address this emerging issue, new technologies must be evaluated and integrated into the electric power system. This study

investigates the impact of a high-inertia flywheel energy storage system (FESS) on the frequency control of the isolated

microgrid of Lipari Island in Italy. A newly deployed monitoring infrastructure provides high-resolution frequency

measurements at 160 ms intervals, enabling the development and validation of a detailed digital twin in DIgSILENT

PowerFactory, incorporating finely tuned synchronous generator dynamic models. To assess the impact that a FESS has on the

microgrid frequency control, the same contingency events are analysed under two distinct scenarios: 2026 and 2030, the latter

characterised by a higher penetration of RES. In the first scenario, the FESS enhances system performance relative to the

baseline case without it. The contribution of the FESS to the isolated microgrid frequency control reduces the nadir and the rate

of change of frequency (RoCoF) by 18% and 22%, respectively. In the second scenario, with a lower system inertia, the

contribution of the FESS drastically increases the reliability of the system since it is necessary to prevent frequency collapse.