Table of Contents
Flywheel Storage
Flywheels store kinetic energy in rotation. Modern systems use carbon fiber rotors, magnetic bearings, and vacuum enclosures for high speed with minimal friction. They offer fast charge/discharge, unlimited cycle life, and no degradation, making them ideal for grid frequency regulation, UPS, and regenerative braking.
Energy scales with the square of angular velocity, so doubling speed quadruples stored energy. Material tensile strength limits maximum speed because centrifugal forces increase with the square of speed. Carbon fiber allows tip speeds of 1000-1500 m/s versus 200 m/s for steel.
Formula
Comparison
| Storage | Wh/kg | Cycle Life |
|---|---|---|
| Steel flywheel | 5-10 | >1M |
| Composite flywheel | 50-100 | >1M |
| Li-ion battery | 150-250 | 500-5000 |
| Supercapacitor | 5-15 | >500K |
FAQ
What limits speed?
Rotor tensile strength vs centrifugal force. Carbon fiber reaches 1000-1500 m/s tip speed. Steel fails around 200 m/s. Composite rotors disintegrate into fibers (safer) vs steel fragments.
How efficient?
85-95% round-trip for short duration (seconds to minutes). Self-discharge 1-5%/hour even with magnetic bearings and vacuum. Best for high-power, short-duration applications.
Are they dangerous?
High-energy rotors need containment. Modern composites fail into fibers (safe). Steel flywheels produce dangerous fragments. All commercial systems use heavy containment vessels as standard safety measure.