This summer, an innovative 20 megawatt capacity flywheel energy storage plant was officially opened in Stephentown, New York.  The plant, the largest of its type in service in North America today, will be used by the New York Independent System Operator to help store excess energy when power generated exceeds the load. When load levels increase, the energy can be delivered back to the grid.

Beyond acting as a buffer for variable load levels, the flywheels will also help with frequency regulation. In that regard, all of the Independent System Operators that operate regional grids in the United States keep the electric frequency at 60 hertz. When the supply of electricity exactly matches the demand, grid frequency is held at a stable level. However, when there is a mismatch in supply and load, operators have had to slightly modify power output up and down to balance loads and smooth out frequency differences.

Load balancing and frequency regulation are important today, but system operators expect greater challenges in the near future as more electricity is generated from renewable sources. The reason: The variability of wind, hydro, and solar power can lead to imbalances between supply and load levels.

To store energy and regulate frequency, the Stephentown plant uses 200 flywheels from Beacon Power Corp. The cylindrical shaped flywheels have a rotor that spins to store and deliver energy. To store energy, the flywheel’s motor draws power from the grid and accelerates the rotor to a higher speed. When delivering power back to the grid, the inertial energy of the rotor drives a generator.

A single flywheel spinning at top speed can deliver 25 kilowatt-hours of energy at a 100 kilowatt power level for 15 minutes. The plant gets its 20 megawatt storage capacity by connecting 200 flywheels in parallel.