Energy storage is key to integrating renewable power. Superconducting magnetic energy storage (SMES) systems store power in the magnetic field in a superconducting coil. Once the coil is charged, the current will not stop and the energy can in theory be stored indefinitely. This technology avoids the need for lithium for batteries. The round-trip efficiency can be greater than 95%, but energy is needed for the cooling of the superconducting coil, and the material is expensive. So far, SMES systems are primarily used for improving power quality through short time storage, but further applications are being researched.