A view of 100 flywheels, inside the blue cylinder-shaped structures, out of a planned 200 installed in a 20-megawatt storage system.

Beacon Power later this month expects to complete installation of a flywheel energy storage system on the grid, which the company says is the largest in the world.

The company said today it plans to host a ceremony for the 20-megawatt energy storage system in Stephentown, N.Y., where the flywheels supply short bursts of power to maintain a steady frequency over the grid. The storage system takes the place of natural gas plants, which grid operators ramp up and down to create an even match between electricity supply and demand.

The expected completion of the plant is a milestone for flywheel-based storage, which has been used for tests and smalle, 1-megawatt systems. Beacon Power's spinning flywheels, which are made of carbon fiber and levitated in a vacuum by magnets, absorb energy from the grid and discharge 1 megawatt for as much as 15 minutes.

The company, which received a $43 million Department of Energy loan guarantee for the plant, plans to use the same flywheel-based system for other energy storage applications, such as buffering power production from wind farms. Flywheels compete with truck-container-size lithium ion batteries which have been used on the grid for similar uses.

Beacon Power's business model has helped get the technology onto the grid. Rather than sell hardware to utilities, it sells grid services, such as frequency regulation, to grid operators normally supplied by natural gas plant operators. It owns and runs the plants.

Flywheel storage has been used as backup power for telecommunications systems but only started being used on the grid in the past few years. Beacon Power said that 18 megawatts worth of power is now online and that the system will be fully commissioned later this month. The opening ceremony is June 12.