Flywheel Energy Storage

Overview

A flywheel stores electricity as motion. Spin a heavy rotor up to tens of thousands of rpm and it holds energy in its rotation; slow it back down and that energy comes out again as electricity. Unlike a battery, a flywheel does not wear out chemically, it can be cycled hundreds of thousands of times and responds in milliseconds, which makes it well suited to short, frequent jobs: smoothing grid frequency, bridging the gap until a backup generator starts, or catching the energy of a braking machine. The engineering challenge is friction and safety: keep the rotor spinning with almost no loss, and contain it if it ever fails.

How it works

The store of energy is the Flywheel Rotor, a composite-over-steel mass on a central shaft. Two things let it spin nearly free of friction. The Bearing System levitates the shaft on active magnetic bearings so nothing touches it, with mechanical touchdown bearings standing by for a safe coast-down if power is lost. And the rotor turns inside the Vacuum System, a sealed chamber pumped down to near-vacuum so there is almost no air to drag against. Together these cut the standby loss to a trickle, which is why a charged flywheel can idle for a long time.

Charging and discharging both run through the Motor-Generator, a single permanent-magnet machine on the shaft. To store energy it acts as a motor, spinning the flywheel up; to release it the same machine acts as a generator. Either way the power flows through the Bidirectional Converter, a four-quadrant IGBT stage that pushes current into the machine when charging and rectifies its variable-frequency output back to grid AC when discharging.

Holding the whole thing together is the Controller & Display supervisor, which coordinates the magnetic bearings, the machine and the converter in real time. Because a high-speed rotor carries enormous kinetic energy, the assembly sits inside a heavy Containment Housing designed to arrest any fragments should the rotor ever burst.