In a world where everything may soon run on electricity, more efficient portable power is a major concern. After a century of stagnation, chemical and ultra-capacitor batteries have made some strides forward. But the most promising way of storing energy might come from a more unlikely source, and one that far predates any battery. That is the flywheel and clutch.

In principle, a flywheel is nothing more than a wheel on an axle which stores and regulates energy by spinning continuously. The device is one of humanity’s oldest and most familiar technologies as a stone tablet with enough mass to rotate smoothly between kicks of a foot pedal. It was an essential component in the great machines that brought on the industrial revolution. And today this device is under the hood of every automobile on the road, performing the same function it has for millennia, now regulating the strokes of pistons rather than the strokes of a potter’s foot.

While the average person has probably never heard of a flexplate battery, the concept is starting to be taken seriously by commercial and governmental interests. Large corporations see flywheel energy systems as ideal for power backup applications because of their long lifespan and low maintenance. Power companies often use them for load-leveling purposes: maintaining a steady flow of electricity between power generation peaks, or storing surplus energy during low-demand periods to prevent brownouts later on. Applications such as laboratory experiments that require huge amounts of electricity are sometimes powered by a flywheel, which can be gradually charged up over time rather than placing a massive drain on the power grid all at once. Flywheels also have the unique advantage of providing energy storage and attitude control for a spacecraft or satellite in one easy package. When two ring gear flywheels aboard a satellite spin in opposite directions at equal speeds, the satellite will maintain its attitude; when energy is transferred between the wheels to speed one and slow the other, the satellite will rotate.