National Renewable Energy Laboratory

Learning About Renewable Energy

Superconducting Magnetic Energy

Photo of two hands holding a somewhat square-shaped battery module about the same size as a conventional battery used in cars. The batteries in the module are long, silver and cylindrical.

Lithium-ion batteries, such as this module used in a hybrid electric vehicle, are much smaller than lead-acid batteries of similar capacity.

Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current through a large coil of superconducting material that has been super-cooled. In low-temperature superconducting materials, electric currents encounter almost no resistance, greatly enhancing their storage capacity.

Power is available almost instantaneously from SMES systems, and very high power output is provided for a brief period of time. There are no moving parts. However, the energy content of SMES systems is small and short-lived, and the cryogenics (super-cooling technology) can be a challenge. Researchers are trying to find ways to maintain the special qualities of SMES without having to keep the systems quite so cold. Low-temperature SMES cooled by liquid helium is commercially available today, and "high temperature" (less cold) SMES cooled by liquid nitrogen is in development.

SMES systems are used to address power quality problems and short-term power losses, such as those that may occur while switching from grid electricity to a backup power supply. They have also been used for electricity-grid support, helping to prevent voltage collapse, voltage instability, and system outages.