Page - 158 - in Water, Energy, and Environment - A Primer

rpm the flywheel can store and deliver 25kWh of extractable energy. Advanced flywheel energy systems can spin at speeds from 20,000 to over 50,000 rpm in a vacuum enclosure. Such flywheelscancomeup tospeed inamatterofminutes. In addition to providing a steady source of electricity, a flywheel may also be used to supply short pulses of energy at high power levels that exceed the abilities of its own energy source.This is achievedby accumulating energy in the flywheel over a period of time, at a rate that is compatible with the energy source, and then releasing energy at amuch higher rate over a relatively short timewhen it is needed. An obvious issue associated with flywheels is catastrophic failure. With rotors moving at high rotational speeds and the flywheel structure experiencing large physical stresses, what would happen if a flywheel flew apart? The industry addresses this possibility by using in-ground concrete foundations to ensure a stable platform to support each high-speed spinning mass. This ensures that any problemwith a single flywheel is contained and cannot affect other units. Advantages of a flywheel are high energy density and substantial durability that allows them to be cycled frequently with no degradation in performance. They also have very fast response and charge/discharge rates, being able to go from full discharge to full charge quickly. They are particularly well suited for high-power, relatively low-energy applications. 9.2.4 Superconductingmagneticenergy storage (SMES) Superconducting magnetic energy storage (SMES) devices store energy in the magnetic field of a circulating dc electrical current in a superconducting coil. The cooled superconductor (at liquid nitrogen temperatures or lower) has no electrical resistance and the current continues indefinitely unless its energy is tapped by discharging the coil. A typical SMES Water,Energy, andEnvironment–APrimer158