Design of a 1 MJ/100 kW high temperature superconducting magnet for energy storage

Abstract

With significant progress in the manufacturing of second-generation (2G) high temperature superconducting (HTS) tape, applications such as superconducting magnetic energy storage (SMES) have become promising for implementation in the electricity grid. Compared to Li-ion batteries, SMES can provide higher power levels at a lower capital cost (down to $200/kW), they have a longer lifetime (over 20 years) and a comparable cycle efficiency of over 95%. Nevertheless, SMES technology is still underdeveloped, which is reflected in the lack of large-scale 2G HTS SMES units. One of the main challenges is designing an optimal magnet that can persistently store energy while withstanding the forces arising from the magnetic field and maintaining a temperature below the critical transition value. This paper outlines a methodology of designing a 2G HTS SMES, using Yttrium-Barium-Copper-Oxide (YBCO) tapes operating at 22 K. The target storage capacity is set at 1 MJ, with a maximum output power of 100 kW. The magnet consists of a stack of double pancake coils designed for maximum storage capacity, using the minimum tape length. The properties of a commercial YBCO tape published in the literature are used to derive the equations for scaling the critical current with magnetic field intensity and direction, as well as operating temperature. The inductance of the resulting coil configuration is calculated analytically, and is used for estimating the total storage capacity of the magnet. Finally, the properties of the superconducting magnet are summarised in a table.