Flywheels Keep the Grid in Tune

Spinning masses face off against big batteries in the half-billion-dollar market for grid stability

Photo: Beacon Power Corp.
Revved Up: A flywheel generator is lowered for high-speed tests.




The task of frequency regulation has never been a great fit for power plants. Generators operate most efficiently when held steady at high output, so holding capacity in reserve and ramping output up and down increases emissions and fuel costs. And because many power plants take a minute or longer to respond to dispatch signals, much of their contribution is ineffectual or sometimes even counterproductive.

"By the time they get around to responding, things are already going in another direction," explains David Hawkins, a senior principal consultant for the Netherlands-based energy consulting firm Kema, who until last year was lead engineer for integrating renewable energy at California's grid operator.

In contrast, the Stephentown flywheels can switch from full output to full absorption in just a few seconds. Such flexibility means the flywheels can deliver at least twice as much frequency regulation from each megawatt of capacity as a typical natural-gas-fired power plant while cutting carbon emissions in half, according to Hawkins.

Such performance should translate into steady revenues under today's frequency regulation rules—and considerably more as the rules shift. Generally speaking, the independent system operators (ISOs) that manage regional power markets buy frequency regulation services by renting control over tranches of generation capacity. Because they respond more quickly, flywheels are likely to be called upon ahead of power plants. Judith Judson, Beacon's vice president for asset management and market development, says that's been Beacon's experience at Stephentown, which started up in January with 8 megawatts of flywheel capacity and was scheduled to reach its full 20-MW design capacity in June.

Judson says that revenues could triple under an order proposed by the U.S. Federal Energy Regulatory Commission in February that requires ISOs to compensate frequency regulators based on their performance. "If you set aside 20 MW and you're called upon a lot because you can respond fast, you're paid more," says Judson. New England's ISO already has such a "mileage" system under pilot rules, expected to be formalized this year. PJM Interconnection, the grid operator for the mid-Atlantic states, also announced plans for performance pricing, and Beacon is readying a $50 million, 20-MW plant in Hazel Township, Pa., to take advantage of it.


If facilities such as AES's succeed, frequency regulation could soon be lithium batteries' biggest market. Sanyo Electric, the market leader in lithium-ion battery production, bets that frequency regulation and other grid applications will account for two-fifths of lithium battery sales in 2020. Electric vehicles and consumer electronics will split the rest of the $60 billion market, Sanyo predicts.

Photo: Beacon Power Corp.
Drumroll, Please A carbon-fiber flywheel is removed from a coating chamber.

Beacon, for its part, bets that the apparent cost advantage of batteries will literally erode with time, as constant cycling degrades their capacity. The company says its flywheels in Massachusetts experience the equivalent of 6000 cycles of full charge and discharge or more per year and are designed to withstand that abuse for 20 years, with minimal maintenance or performance degradation.




So in the future, the frequency regulator could be you.