super magnetic energy storage (SMES)
Magnetic energy storage in superconducting coils, Super Magnetic Energy Storage (SMES), is based on superconductors. These are conductors that have no ohmic resistance at temperatures around absolute zero. These superconductors form the basis of the SMES principle.
In energy storage, excess alternating current is taken from the power grid, rectified and fed into the SMES coil as direct current. For the SMES effect to work, the coil must be constantly cooled below the superconductor's transition temperature. The SMES coil has no ohmic resistance, so the injected current used to establish a magnetic field does not decrease. As a result, the energy stored in the magnetic field is permanently available. The electrical energy is regenerated by decaying the magnetic field. The direct current then generated is converted to alternating current by an inverter and fed back into the power grid. The SMES coil is then discharged.
The SMES process itself has high efficiency, but the current conversion from AC to DC and the reconversion from DC to AC have some losses. In addition, the cost ofcooling the coil is quite high.