TYNGSBOROUGH, Mass. - Spinning flywheels have been used for centuries for jobs from making pottery to running steam engines. Now the ancient tool has been given a new job by a Massachusetts company: smooth out the electricity flow, and do it fast and clean.

Beacon Power's flywheels - each weighing one ton, levitating in a sealed chamber and spinning up to 16,000 times per minute - will make the electric grid more efficient and green, the company says. It's being given a chance to prove it: the U.S. Department of Energy has granted Beacon a $43 million conditional loan guarantee to construct a 20-megawatt flywheel plant in upstate New York.

"We are very excited about this technology and this company," said Matt Rogers, a senior adviser to the Secretary of Energy. "It's a lower (carbon dioxide) impact, much faster response for a growing market need, and so we get pretty excited about that."

Beacon's flywheel plant will act as a short-term energy storage system for New York's electrical distribution system, sucking excess energy off the grid when supply is high, storing it in the flywheels' spinning cores, then returning it when demand surges. The buffer protects against swings in electrical power frequency, which, in the worst cases, cause blackouts.

Such frequency regulation makes up just 1 percent of the total U.S. electricity market, but that's equal to more than $1 billion annually in revenues. The job is done now mainly by fossil-fuel powered generators that Rogers said are one-tenth the speed of flywheels and create double the carbon emissions.

Beacon said the carbon emissions saved over the 20-year life of a single 20-megawatt flywheel plant are equal to the carbon reduction achieved by planting 660,000 trees.

Flywheels also figure into the emerging renewable energy market, where intermittent energy sources such as wind and solar provide power at wildly varying intensities, depending on how long the breeze blows and sun shines. That increases the need for the faster frequency buffering, Rogers said.

Dan Rastler of the Electric Power Research Institute, an industry research group, added that if a carbon tax is passed by Congress, flywheels start looking a lot better than fossil-fuel powered alternatives.

Beacon's flywheels, massive carbon and fiberglass cylinders, have already been tested on a small scale in New York, California and the company's Tyngsborough offices. Chief executive officer Bill Capp hopes the Stephentown, N.Y., plant will be up and running by the end of 2010.

Flywheels are rotating discs or cylinders that store energy as motion, like the bicycle wheel that keeps rotating long after a pedal's been turned.