Beacon Power, a company that manufactures and installs flywheel energy storage systems, says that it is completing the installation of the largest FESS (Flywheel Energy Storage System) in the world for the purpose of frequency regulation. When generator speeds are adjusted (but not much, due to impracticality) to meet power demand, frequency changes as well. This is due to the fact that generator speed is increased so that they generate more electricity, and frequency increases with speed.
Flywheels can be “charged” with AC or DC if designed to do so. Generators generate AC. Batteries can only be charged with DC (which means not alternating), and a consequence of that is that the power from generators has to be converted from AC to DC with a rectifier and then the batteries supply DC power to a device which converts it back to AC. There is a cost associated with the batteries and the rectifier and energy is lost in this process as well.
Anyway, keep in mind that the main purpose of this project is frequency regulation, rather than storing energy for later use, but it does both. It supplies short bursts of power to the electricity grid to help maintain the appropriate frequency.
A flywheel is a wheel which a motor spins when it is supplied with electricity from any type of generator and, after the motor is shut off, the wheel continues to spin for a while. It can spin for seconds, minutes, or hours at a time. Flywheels can also be called power bufferers.
This FESS project is to store 20 MW of power and is expected to be commissioned later this month. The opening ceremony is on July 12.
The need for energy storage is increasing as peaking generators (which are turned on to compensate for electricity shortages) become more expensive to operate, and as more variable/intermittent solar and wind power plants are constructed.