From Damn Interesting:
In a world where everything from our automobiles to our underwear may soon run on electricity, more efficient portable power is a major concern. After a century of stagnation, chemical and ultracapacitor batteries have recently made some strides forward, and more are on the horizon. But the most promising way of storing energy for the future might come from a more unlikely source, and one that far predates any battery: the flywheel.
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: it was in the potter’s wheel six thousand years ago, 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 it’s 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.
Ongoing research, however, suggests that humanity has yet to seize the true potential of the flywheel. When spun up to very high speeds, a flywheel becomes a reservoir for a massive amount of kinetic energy, which can be stored or drawn back out at will. It becomes, in effect, an electromechanical battery....MORE