Flywheel are efficient for high power in short duration: https://en.wikipedia.org/wiki/Flywheel_energy_storage https://en.wikipedia.org/wiki/Flywheel_energy_sto

Flywheel are efficient for high power in short duration: https://en.wikipedia.org/wiki/Flywheel_energy_storage https://en.wikipedia.org/wiki/Flywheel_energy_storage Usually used during a short period of time before the diesel generator can be fully operational.