Superconducting magnetic energy storage (SMES)

Superconducting magnetic energy storage 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.

Which is why SMES has been proposed as a storage option to support large-scale use of photovoltaics and wind as a means to smooth out fluctuations in power generation.

An advantage of SMES is that power is available almost instantaneously, and very high power output is provided for a brief period of time. There is no loss of power, and there are no moving parts. A disadvantage is that the energy content of SMES systems is small and short-lived, and the cryogenics (cold temperature 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.

Applications of SMES

Already dramatically used in such applications as high-speed, magnetic-levitated trains, superconductors are also being developed for use in microelectronics and communications.

SMES is also used in utility applications. Several 1-MW units are used for power quality control in installations around the world.

In northern Wisconsin, a string of distributed SMES units was deployed to enhance stability of a transmission loop. The transmission line is subject to large, sudden load changes due to the operation of a paper mill, with the potential for uncontrolled fluctuations and voltage collapse. Besides stabilizing the grid, the six SMES units also provide increased power quality to customers served by connected feeders.


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