lecture 4 - Flywheels.pdf(energy storage systems)
- 1. Energy Storage Systems Flywheel Energy Storage
- 2. Introduction ❑ A flywheel, in essence is a mechanical battery - simply a mass rotating about an axis. ❑ Flywheels store energy mechanically in the form of kinetic energy. ❑ They take an electrical input to accelerate the rotor up to speed by using the built-in motor and return the electrical energy by using this same motor as a generator. ❑ Flywheels are one of the most promising technologies for replacing conventional lead acid batteries as energy storage systems.
- 3. Theory of Flywheels Kinetic energy: where I is the moment of inertia and ω is the angular velocity of a rotating disc. For a solid cylinder: 𝐼 = 0.5 𝑚 𝑟2 So, the energy is increased if ω increases or if I increases. I can be increased by locating as much mass on the outside of the disc as possible. But as the speed increases and more mass is located outside of the disc, mechanical limitations are more important. 2 1 2 k E I =
- 4. Design of flywheel energy storage system Flywheel systems are best suited for peak output powers of 100 kW to 2 MW and for durations of 12 seconds to 60 seconds . The energy is present in the flywheel to provide higher power for a shorter duration, the peak output designed for 125 kw for 16 seconds stores enough energy to provide 2 MW for 1 second.
- 5. Flywheel Energy Storage System
- 6. Component of FESS Flywheel Motor/Generator Power Electronics Magnetic bearings External Inductor
- 7. Motor/Generator Permanent Magnet (PM) machines have the most advantages, including higher efficiency and smaller size when compared with other types of motors/generators of the same power rating. PM also exhibit lower rotor losses and lower winding inductances, which make it more suitable for a vacuum operating environment and the rapid energy transfer of flywheel applications. The motor/generator is designed to be operated at high speed for minimize system size.
- 8. Power Electronics Flywheel energy storage system is the three-phase IGBT- based PWM inverter/rectifier. The IGBT is a solid-states device with ability to handle voltages up to 6.7 kV, currents up to 1.2 kA and most important high switching frequencies.
- 9. Bearings Bearings consists of permanent magnets, which support the weight of the Flywheel by repelling forces, and electromagnets are used to stabilize the Flywheel. The best performing bearing is the high-temperature super-conducting (HTS) magnetic bearing, which can situate the Flywheel automatically without need of electricity or positioning control system. HTS magnets require cryogenic cooling by liquid nitrogen.
- 10. External Inductor The high-speed PM machines offer low inductances with low number of stator turns and large operating magnetic air gaps . The low inductances result in High Total Harmonic Distortion (THD) which increases the machine power losses and temperature. Using an external inductor in series with the machine in charging mode is necessary to reduce the THD and bring it within an accepted range.
- 11. Working of a flywheel energy storage system Its work in three mode:- Charging mode Stand by mode Discharging mode
- 12. Future work in FESS • Advanced flywheel system rotate above 20,000 rpm in vacuum enclosure made from high strength carbon composite filament will be very efficient. • The flywheels are not the primary source of power generation. • Rather, when there is too much power on the grid, it is shunted to the flywheel facility and used to set the flywheels in motion. • Then, when the power is needed a few seconds or minutes later, the momentum of the flywheels is used to generate power back into the grid.
- 13. ADVANTAGES • High power density. • High energy density. • No capacity degradation, the lifetime of the flywheel is almost independent of the depth of the discharge and discharge cycle. It can operate equally well on shallow and on deep discharges. Optimizing e.g. battery design for load variations is difficult. • No periodic maintenance is required. • Short recharge time. • Low sensitivity to temperature since they are operating in a vacuum containment • Scalable technology and universal localization. • Environmentally friendly materials, low environmental impact
- 14. Disadvantages of FESS • Complexity of durable and low loss bearings • Mechanical stress and fatigue limits • Material limits at around 700M/sec tip speed • Potentially hazardous failure modes • Short discharge time
- 16. Example In order to minimize automotive emissions, a potential approach involves utilizing the stored energy within a spinning flywheel. Consider a scenario where a car weighing 1100 kg incorporates a cylindrical flywheel with a diameter of 1.50 m and a mass of 270 kg. This setup aims to enable the vehicle to cover a distance of 350 km without a spin-up of the flywheel. (a) Estimate the total energy needed to be stored in the flywheel to provide the car with thirty acceleration periods from rest to 95 km/h (average frictional force on car = 450 N). (b) What is the angular velocity of the flywheel when it has a full “energy charge”? (c) How long would it take a 150-hp motor to give the flywheel a full energy charge before a trip?
- 17. Example (a) The initial energy of the flywheel is used for two purposes: to give the car translational kinetic energy 30 times, and to replace the energy lost due to friction.
- 18. Example (b) (c) The work done by the motor is equal to the kinetic energy of the flywheel.