Flywheels and Energy Storage

Nine out of ten dentists agree that the wheel was a pretty great invention. But modern scientists and engineers aren't just content to let a millennia-old technology like that sit around gathering dust. No, the modern wheel has many more uses than chariot races and wheat grinders (NASCAR races and blenders, to say the least).

One application of the simple fact that once you get a large wheel turning, it's hard to stop: the flywheel. The idea's been around for a while—just look at an old potter's wheel:

The potter kicks a pedal attached to the wheel, and it starts to spin. Once up to speed, it will keep the lump of clay on the table spinning with minimal additional effort—just the occasional kick to fight frictional losses.

An industrial flywheel, used for energy storage the same way your car uses a battery, is basically the same thing: a large rotating wheel or cylinder that is spun up to high speed like an electric motor.⁷ Once up to speed, the flywheel's enormous moment of inertia ensures that a) it's very hard to stop, and b) it can store a tremendous amount of energy, as given by .

An additional benefit of the flywheels is their ability to be used as a backup generator, much like an emergency diesel engine.⁸ If something disastrous were to happen to the electricity grid, physics means the flywheel keeps on spinning. You can continue to pull energy out of it until it slows to a halt.

Because flywheels can provide the same security as a backup generator—with the additional benefit of having zero startup time (the wheel's already spinning when the power goes out, so there's no need to fire up the generator)—they're an intriguing option for buildings that have to hedge against any sort of power fluctuation, such as data centers, which store all the information for large companies' websites. Any time a data center goes down, taking with it your Facebook photos or tweets or, you know, maybe $2 million in profit, people get a little angry. Flywheels provide a totally non-polluting option for ensuring the world can keep watching cat videos, no matter what's going on outside their houses.