Anything to do with energy storage attracts us, although a flywheel energy storage system is very different from a battery. Flywheels can store grid energy up to several tens of megawatts. If we had enough of them, we could use them to stabilize power grids. Batteries also started out as small fry, so we should not write off flywheels any time soon.
How Does a Flywheel System Store Energy?
A flywheel is a mechanical device, that stores and releases rotational energy. Imagine, as an example, a heavy wheel that keeps on spinning, storing the energy that set it in motion.
The principles of a modern flywheel are set out in the above diagram. A rotating cylinder spins freely on magnetic bearings, in a vacuum enclosure. An electric motor sets the cylinder spinning during low demand. And then, when the user wants the energy, the electric motor becomes a generator.
A flywheel energy storage system is therefore functionally similar to a hydro power station, that stores gravitational energy in water. In that instance, an electric motor pumps water uphill during low demand. During peak demand an operator releases the water downhill, through electric motors operating in generator mode.
Does This Sound Like a Battery Energy Storage System?
It probably does, because utility grids recharge battery farms during off-peak periods, and then reclaim the energy during high demand. Power utilities need innovative ways to store renewable wind and solar energy, during low demand periods, so they can release it after sunset when demand is high.
Practical Applications for Flywheel Energy Storage
- Several innovative power utilities already use flywheel storage systems to maintain power grid frequency.
- Renewable energy is knocking on flywheel energy’s door. The system can respond instantly, unlike battery storage.
However on the downside, flywheel energy storage systems have low energy storage density per unit of weight and volume. Beacon Power operates a 25 kilowatt / 100 kilowatt-hour system in New York. The 200 flywheels reach 15,000 revolutions per minute at peak speed.
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