For millennia, flywheels have powered everything from potter's wheels to steam engines, storing kinetic energy in their momentum as they spin. Now, the flywheel has found a higher purpose in the electrical grid.
Wound around a 500-pound rotor, this 5-foot-tall, 3-foot-diameter flywheel assembly at Beacon Power's plant in Tyngsboro, Mass., appears poised to be the great green hope of that unsung, unsexy, absolutely essential energy niche that is frequency regulation.
"Okay, bring her down," the technician shouts, and, slowly, the massive flywheel is lowered into place, the brunt of its weight shouldered by a ring of ultra-powerful magnets. Capped and sealed and pumped to a vacuum roughly equivalent to that of near-Earth orbit, the flywheel's motor will use excess power in the grid to accelerate the massive wheel to speeds of up to 16,000 rpm, effectively storing the surplus electricity in its own momentum.
Then, when grid power dips, it will switch its motor into generation and draw on the inertia of its flywheel, heavy as a Honda Civic and spinning faster than an F-16 flies, to feed the formerly excess power back into the grid. The goal is to keep supply in perfect concert with demand, maintaining the frequency of alternating current at as close to 60 cycles per second as possible. Too much power in the grid drives its frequency up, too little drives it down, and too much variation in either direction means fines for utilities, wasted energy and, in extreme cases, brownouts.
"Electricity is a net-zero sum game," Bill Capp, Beacon Power's CEO, says. For just over a year, the array of 12 flywheels sunk into Beacon's concrete floor has been helping keep lights steady on the northeast grid. In a cornfield just across the New York border, the company recently broke ground on an array of 200 flywheels, comprising some 20 megawatts of capacity.
When complete in 2011, it will be the first large-scale flywheel frequency-regulation plant in the world, and the beginning of what may be a new paradigm for this crucial and growing component of the electric grid.
"What happens today is you essentially make a power plant do unnatural things to provide frequency regulation," says Matt Rogers, a senior advisor at the Department of Energy. "You jerk it around a lot relative to the way you'd like to run it," he says.
In other words, if a thousand people make toast in Philadelphia, something has to provide that extra power and so, somewhere, a generator labors into operation. Up comes the toast; off goes the generator. Not only is this inefficient, it's also very expensive: Fossil fuel generators lose up to 98 percent of capacity pulling frequency regulation duty, held back by how quickly they can cycle on and off.
"The Beacon approach does this at a much lower cost," Rogers says, and with fewer carbon dioxide emissions. Plus, he says, "It actually does it faster than a natural gasfired power plant and it allows the natural gas plant to run itself more efficiently."
The DOE recently guaranteed $43 million worth of loans for Beacon's New York plant.
"Energy storage technology and frequency regulation are areas where we see a great deal of innovation and where we see a very large market need," Rogers says. "And that combination is something that makes the department pretty excited."
The 200 flywheel units, arranged in independent arrays of 10, will supply roughly 10 percent of the New York grid's frequency regulation when complete. Hovering magnetically in a vacuum, wear and tear on the flywheels themselves is virtually nil.
Operated remotely from Beacon's headquarters on the Merrimack River, the plant is expected to last at least 20 years and cost roughly $69 million to build, with future plants costing something close to half that. Two more large-scale facilities, one in New England and another at an undisclosed East Coast location, are in the works.
Coming decades promise more demands on the grid's resources as wind and solar plants, veiled by passing clouds and spiked by sudden gusts, create more intermittent production just as plug-in hybrids are expected to create more demand. Grid operators are betting on a new generation of technologies to make the grid faster, smarter and more reliable. If Beacon's Stephentown project is successful, flywheels may hold the most ancient pedigree among them.