Greentech Media

Flywheels: Flywheels are large discs that spin, storing energy as motion. They function based on the principal of inertia, like tops, potter's wheels, satellites and other gyroscopes. A trickle of electricity keeps flywheels spinning, but when the electricity is cut, the spinning slows and energy gets sent the other way.

They usually provide only about 15 seconds of so-called "bridge power," enough to bridge the time needed for a generator to kick in, and also to deal with the 90 percent of outages that only last a few seconds.

A Short History: Flywheels originally were intended to recapture energy from hybrid cars' brakes, but hit an obstacle when it turned out they made it difficult to turn the cars. When the industry moved to stationary applications, the target market was still unclear.

Beacon went public in 2000, focusing on the telecom market, while Active Power, another flywheel company, went public and focused on Internet data groups. Both companies took a beating when dot-com and telecom bubbles burst.

Then Active started targeting customers like banks and hospitals, which have much to lose if power fails, but which also are notoriously shy of new technology. And Beacon decided to target frequency regulation for the grid, which also requires a high level of proof.

Sales in the flywheel industry began picking up in 2004, which Farah Saeed, a senior consultant for Frost & Sullivan, called the turning point in the market. But the increase of some 40 percent per year since then has not included Beacon, which hasn't yet reached commercialization.