I suspect the problem with large flywheels is the energy they use just to keep going, especially if they are going fast which they need to be to store significant amounts of energy.
I recollect working on a flywheel based UPS system which had multiples of 2MW generators each associated with a flywheel rotating at twice synchronous speed which was magnetically coupled to the generator / motor shaft. My recollection was that each unit consumed 50kW when not being used just overcoming air resistance. The flywheel carries the 2MW load for just 3 seconds but this was long enough to start a diesel generator.
I suspect the problem with large flywheels is the energy they use just to keep going, especially if they are going fast which they need to be to store significant amounts of energy.
I recollect working on a flywheel based UPS system which had multiples of 2MW generators each associated with a flywheel rotating at twice synchronous speed which was magnetically coupled to the generator / motor shaft. My recollection was that each unit consumed 50kW when not being used just overcoming air resistance. The flywheel carries the 2MW load for just 3 seconds but this was long enough to start a diesel generator.
