How Do Flywheel Energy Storage Systems Work?
Flywheel Energy Storage Systems turn electrical energy into kinetic energy by accelerating a wheel very fast and harvesting energy later by slowing it down.
- Pros: high power density, long lifetime, high efficiency, carbon-free
- Cons: mechanical stress, material durability limits, shorter discharge times
FESS Interior Design
- A flywheel contains a dual-function electrical motor to store and generate energy
- When discharging energy rotor is turned on and slows down the motor
- The rotor acts as a generator and outputs electrical energy
- Bearings are put in place to resist rotational forces to maintain their position
- Problem: requires high-performance lubricants and frequent maintenance
- Solution: magnetic bearings are used so that there’s no friction
- The enclosure acts as a container for the FESS
- The power electronic converter converts kinetic energy into electrical energy
- Limitations
- Speeding up the flywheel increases the centrifugal force (F = mw2r) which strains the material → high tensile strength in the material is required
- Resistance of the material limits the amount of energy able to be stored
Rotational Energy Equation: K = 0.5Iw2
- K = Rotational Energy
- I = Rotational Inertia
- w = Angular Velocity
- Rotational mass is proportional to rotational inertia
Low-Speed vs. High-Speed FESS
- Low-Speed FESS: made up of steel
- Spin at up to 10,000 RPM
- Housed in a traditional smaller scale mechanical enclosure
- High-Speed FESS: made up of carbon/fiberglass (high strength-to-weight ratio)
- Spin at up to 100,000 RPM
- Housed in a vacuum utilizing magnetic bearings to minimize friction
Costs
- FESS costs on average $1,500-$6000/kWh (2016)
- Largely due to installation costs with very few maintenance costs
- Li-ion costs on average $200-1,260/kWh (2016)
- Hybrid FES/Li-ion Systems can potentially reduce costs
