> I wouldn't wonder if there were already plans for building large rotating masses with motors on them that are kept at network frequency, with the motors switc

> I wouldn't wonder if there were already plans for building large rotating masses with motors on them that are kept at network frequency, with the motors switching over to serve as generators when the frequency drops. Flywheels? Yes: https://en.wikipedia.org/wiki/Flywheel_energy_storage#Grid_energy_storage https://en.wikipedia.org/wiki/Flywheel_energy_storage#Grid_e....