Flywheels and small mechanical stores
Spinning rotors that store motion, and springs and hydraulic accumulators.
Storage · Mechanical · No. 80
- Storage
- Duration: Seconds to minutes
Carbon-fibre rotors spinning at about 16,000 rpm in vacuum help keep the grid's frequency steady, cycling up to 175,000 times.
Chart: Illustration: Flywheels and small mechanical stores
Where it comes from
Chart: Map of where it comes from
A motor spins a heavy rotor of steel or carbon fibre, and to discharge the same machine becomes a generator as the rotor slows.
Three things to know
- Stored energy rises with the square of speed, so modern rotors spin very fast inside vacuum casings.
- A flywheel can lose up to 15% of its charge an hour, so it suits seconds and minutes, not overnight storage.
- China's Dinglun plant cost about USD 1,600 per kW in 2024, about half Stephentown's USD 3,450 (both calculated).
The journey
- 1 Grid powerMotor spins the rotor up to speed
- 2 Spinning rotorSteel or carbon fibre in vacuum
- 3 Magnetic bearingsKeep friction losses low
- 4 GeneratorRotor slows, returning power in seconds
- 5 Grid serviceFrequency control, backup, power quality