Pumped storage is routinely used to store energy. It's not theoretical.
Has Flywheel storage every been seriously used in large-scale commercial applications? Someone mentions it on every energy-storage thread, and I'd like to know if the people suggesting it are just spinning our wheels.
FES is used in non-kill-zone habitable solutions like datacenters, bottoms of passenger trams/hybrid buses and electromagnetic aircraft catapults. The historical issue with FES is unscheduled, rapid disassembly, but carbon/kevlar composites have been shown to have greater integrity with least unsprung structural mass (because you want the most mass as close to the rim as possible to ensure highest moment of inertia.)
FES has 10x specific energy than supercapacitors or batteries with no memory and precise state of charge. Magnetic bearings and hard vacuums make them quite efficient.
The JET fusion reactor in Oxfordshire uses flywheels to provide very large pulses of electricity for short periods of time (a minute or two iirc). The reactor requires too much energy to run directly off the National Grid.
As I recall from a tour I went on of jet 30 years ago there are a large bank of flywheels which spin up over several minutes, these are then rapidly discharged to a bank of capacitors which are then used to power the experiment, I believe the duty cycle was 9 minutes. [1][2]
I believe some electric cars used capacitors to store regenerated electricity from breaking.
"More Ampères please Mister Woodbine." - Road to Welville
Sounds like they use it for high output rather than efficiency though. Still interesting that it has real world applications though. Shows that the technology has potential as well.
It's not even remotely on the same scale. There are three massive utility-level flywheel deployments according to Wikipedia that provide 15 minutes of output.
Edit: Seems the purpose is purely frequency regulation, rather than storage per se.
