Philip LeGoy, senior consultant of power plant design for Ireland’s Electricity Supply Board, says his country is regularly obtaining 25% of its electricity from wind. "If I’ve got 1,000 megawatts of wind power," he says, "it is a detrimental thing when it goes offline."
When the amount of energy provided by wind turbines falls short of the amount of electricity needed to operate a power grid, that grid has to work harder to balance the discrepancy between load and available supply. Demand for energy fluctuates rapidly between high and low load, and power plants often cannot throttle power output to accommodate sudden increases in demand without suffering major repercussions.
Poor grid balance can result in high network losses, equipment overloading, unacceptable voltage and frequency levels, voltage instability, and even outages. These repercussions are "detrimental," to say the least. In order to successfully harness, maintain, and distribute vast amounts of power, the active and reactive power balance in a system must be controlled.
One solution to the grid stabilization problem is to build energy storage plants that connect to the electrical grid. Storage plants help stabilize the grid by quickly providing additional power during periods of high demand (when an intermittent energy source ceases to contribute electricity, for example). In order to accomplish this, the plants store energy during periods of low demand.
A variety of energy storage technologies exist and have been put to use over the years, but some (like pumped storage) require large land areas. From compressed air energy storage to batteries, each technology has its sweet spot. For frequency regulation, though, flywheel energy storage appears to be a strong contender.
A milestone in applying flywheel technology to energy storage was reached when Beacon Power announced the opening of the world’s first grid-scale, 20-MW flywheel energy storage facility in June last year in Stephentown, N.Y. The system provides frequency regulation services to the New York Independent System Operator (NYISO).
Stephen G. Whitley, president and CEO of NISO, which contracts with the plant for frequency regulation services, commented, "New York’s competitive marketplace for electricity provides fertile ground for energy innovations such as Beacon Power’s flywheel system. It’s great to see pioneering technology bringing new solutions to meet New York’s energy needs."
The energy storage plant utilizes 200 flywheels, each weighing more than 2,800 pounds, to store energy that can be transferred to the grid during times of high demand: 5 MWh or 20 MW for up to 15 minutes. In order to store energy, the flywheels rely on mechanical inertia. The flywheel is accelerated by an electric motor that doubles as a generator upon reversal, slowing down the disc and producing electricity. Because friction must be minimized in order to prolong storage time, the flywheel is suspended in a vacuum and employs a sensorless permanent magnet motor drive.
Unlike systems implemented in years past, the flywheel system is clean and energy efficient. A very small percentage of the power is lost as heat during transfer, and the system is able to respond to large demand changes in seconds.
Oztek Corp. developed software and essential control hardware technologies used to interface the large arrays of flywheels to the power grid, the sensorless motor drive, and the grid tie inverter. Dave Zendzian, CTO of Oztek noted that " Due to the high-power nature of the installation, many of the algorithms employed in the controllers needed to be designed using simulation coupled with design verification on smaller-scale hardware platforms. As such, there are always risks and challenges when you attempt to bring up the full-scale system."
And, in fact, there have been a few difficulties with the facility. In July, one of the flywheels at the Stephentown facility experienced serious technical difficulties that were described by many as an explosion. The local paper reported that Beacon Power Communications Director Gene Hunt explained that it wasn’t an explosion; the flywheel came unraveled: "’It failed in the way it is designed to fail,’ he said, ‘It grinds itself into dust.’ It looks terrible but is not dangerous and the sooty material that gets spewed out is actually harmless carbon fiber dust from the unraveled flywheel, he added. An automatic suppression system, he said, acts to keep most of the dust down. There is no toxic material, he said, and the flywheels are well contained in their concrete housings."
Then, in November last year, Beacon Power, which had been operating at a loss, filed for Chapter 11 bankruptcy but continues to operate.
That development put the brakes on a second project, which called for the integration of Beacon’s 1-MW flywheel energy storage system into the 150-MW Dave Gates Generation Station (DGGS) at Mill Creek near Anaconda, Mont. The entire DGGS is unique in that it was built specifically for grid regulation. The flywheel system was expected to be integrated by the end of last year, but in mid-December, the Billings Gazette reported that the flywheel portion of the project was on hold. The paper quoted a company spokesperson as saying that the U.S. Bankruptcy Court in Delaware has put Beacon Power on a tight budget and has not authorized the company to spend any money on the Montana job. The company is focusing on repaying a $39.1 million loan it received from the Department of Energy in 2010, in part by putting the Stephentown facility up for sale by the end of January.
Last August, Beacon Power had announced that it had been awarded a $5 million state grant toward construction of another 20-MW flywheel energy storage plant, this one in Hazle Township, Penn.
Beacon’s Stephentown energy storage plant is sure to remain a valuable grid asset, despite the difficulties this first-of-its-kind facility has faced, because it offers a fast, clean, and relatively inexpensive way to inject power into the grid quickly.
In fact, the market for flywheel storage could heat up, thanks to an October decision by the Federal Energy Regulatory Commission (FERC) that sets a new way grid operators, including NYISO, must pay for regulation services. As FERC sees it: "Adjusting the compensation for regulation service providers will recognize the amount of service resources provide, thus correcting the price signal for faster-ramping resources. This will allow market operators to take advantage of the capabilities of faster-ramping resources to improve operational and economic efficiency of the transmission system and reduce costs to consumers in organized wholesale markets."
—Matthew Hoff is a freelance writer and native Pittsburgher who studied English at the University of Pittsburgh. He specializes in online content writing, focusing on energy and power generation topics. Sonal Patel is POWER’s senior writer.