A bank of 64 large, overhead light bulbs dimmed slightly in a North Austin factory Tuesday as their electric power was cut and a flywheel storage battery briefly took on the load.

It was a demonstration of what Active Power Inc. executives said was the world's first commercially viable flywheel energy storage system. The Austin company, created last year from a company founded in 1992, is chaired by Eric Jones, one of the city's most respected venture capitalists.

The flywheel unit draws less power than an electric hair for the time it takes to get a backup generator running.

The CleanSource name comes from the fact that the flywheel devices would replace the large banks of toxic, lead-acid batteries now used when a plant shifts electric power from a faltering utility connection to backup generators.

The batteries, which Pinkerton said represent a $500 million market, take up lots of room and must be replaced every few years.

He said Active Power spent $3.25 million to develop the 31-inch-diameter CleanSource devices, each of which is computer-controlled and powered by a small electric motor.

They come in tall, refrigerator-size units, are designed to last 20years and take up no more than 10 square feet, according to the company.

And our system is half the cost of the batteries,'' Pinkerton said.

Flywheels are as old as the potter's wheel, a stone wheel so well-balanced that, when pumped to sufficient speed, it maintains its momentum with little extra input.

A version of flywheel technology long has been used in internal combustion engines to balance rotating parts. Use of flywheels as energy storage devices, particularly to power electric vehicles, has been researched for more than 30 years.

Engineers at the University of Texas Center for Electromechanics are developing a flywheel battery, under a $10 million federal research program, for an electric bus.

Active Power's flywheels apparently have several advantages over the UT ones. UT's flywheels would spin at up to 40,000 revolutions per minute and be levitated in a magnetic field inside a sealed vacuum container. That would be surrounded by a hard shield to protect against dangerous shrapnel should the wheel tear itself apart.

Pinkerton said Active Power's flywheel spins to a maximum of 7,500 rotations per minute in a partial vacuum, which he said would prevent it from coming apart.

He said a key to CleanSource's success was its extremely well-balanced flywheel, which is steel rather than the rosin composite material of UT's bus flywheel.

CleanSource's slower flywheels aren't intend to power anything for very long, just to bridge power gaps, glitches and interruptions for semiconductor manufacturers, hospitals, telecommunication centers, computing centers and power utilities.

Company literature says CleanSource units are priced as low as $40 per kilovolt-ampere and are fully compatible with all three-phase uninterruptible power supply systems.

Pinkerton said Active Power, which has 35 employees, including some former students of UT's electromechanics center, has raised $10 million in operating capital in the past few months.

Its first customer, Southern Development -- an Atlanta, Ga., subsidiary of Southern Company, the nation's largest producer of electricity -- is evaluating the devices.

"We have been impressed with the performance of the CleanSource technology," said Kevin Flether, president of Southern Development.

Jim Balthasar, Active Power's vice-president of marketing, said public utilities, facing the prospect of private competition in a deregulated market, should find the CleanSource systems appealing.

They could help maintain customer confidence in the face of periodic power outages caused by storms or mechanical failures.

Officials of Austin's electric utility have expressed interest in CleanSource systems, Balthasar said. They could not be reached for comment.