Flywheels keep the grid in tune

Spinning masses face off against big batteries in the half-billion-dollar market for grid stability - If you think twirling the mass of a family car hundreds of times a second is an unlikely way to keep power grids humming at perfect pitch, think again. Flywheel developer Beacon Power Corp., based in Tyngsboro, Mass., is already making money that way in Stephentown, N.Y., where it operates more than 160 1150-kilogram magnetically levitated flywheel motorgenerators. These machines continuously accelerate and decelerate to balance electrical supply and demand and thus keep New York state??s grid tuned to 60 hertz.