Slide 1
A flywheel stores energy by spinning
A flywheel stores kinetic energy, the energy of motion, in a rotating mass. It can absorb a drive’s surplus energy and return it as the drive slows.
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This smooths intermittent torque, such as repeated pulses from a machine cycle. It does not create a steady external energy supply; it redistributes energy through time.
Slide 2
Moving mass outward increases rotational inertia
Rotational inertia measures resistance to a change in spinning speed. It depends on how far mass lies from the axis.
Moving mass outward can increase stored energy at the same angular speed.
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The ideal energy is one half of rotational inertia times angular speed squared. Doubling speed therefore quadruples energy for unchanged inertia, but also increases material and containment demands.
Slide 3
Taking energy out slows the wheel
A flywheel speeds up while charging and slows while discharging. The usable energy depends on the allowed speed range.
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A machine needing nearly constant shaft speed can use only a limited fraction before the speed deviation becomes unacceptable. Power electronics or gearing can broaden useful operation in other designs.
Slide 4
Friction and air drag drain energy even while waiting
Bearing friction and air drag gradually drain stored energy. Vacuum enclosures and suitable bearings can reduce those losses.
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Cooling, controls and auxiliary equipment also affect whole-system efficiency. Comparing storage technologies requires a stated storage duration, because a short pulse and an overnight hold place different demands on standby loss.
Slide 5
A failing rotor can release the stored energy
A high-speed rotor must withstand internal stresses and remain balanced. Protection must account for the energy released if the rotor fails.
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Material strength limits useful rotational speed. Design also considers resonance and support dynamics, so increasing speed is not a free route to unlimited storage capacity.
Sources
- Electricity Storage Handbook
US Department of Energy / Sandia
- Solar Energy and Storage Basics
US Department of Energy