With the congestion of power lines and their unstable tendencies, strategic injection of brief bursts of real power can play a crucial role in maintaining grid reliability. Small-scale Superconducting Magnetic Energy Storage (SMES) systems, based on low-temperature superconductors, have been in use for many years. These systems enhance the capacity and reliability of stability-constrained utility grids, as well as large industrial user sites with sensitive, high-speed processes, to improve reliability and power quality.

Larger systems, and systems employing superconductors, are a focus of recent development. Flywheels, based on frictionless superconductor bearings, can transform electric energy into kinetic energy, store the energy in a rotating flywheel and use the rotational kinetic energy to regenerate electricity as needed. Conventional flywheels suffer energy losses of 3-5% per hour, whereas superconductor-based flywheels operate at 0.1% loss per hour. Large and small demonstration units are in operation and development. Broad market use of SMES devices is considered long-term.