An Investigation of Superconducting Magnets for a 10 MWh SMES

Storage of off-peak electricity for use during peak hours is receiving more attention due to high capacity baseload generating plants, a growing difference in the cost of generating off-peak electricity compared to peak electricity, and an unpredictable growth in peak demand. In this study, 10 MWh superconducting magnetic energy storage (SMES) systems are analyzed with respect to the potential impact of advancing materials technology. Initial analyses focus on magnet design parameters and costs based upon presently available materials. To determine the impact of materials currently under development, magnet designs are then optimized using advanced materials for which commercial availability is anticipated in the near future. The affects of increased superconductor current density, magnet operating temperature and structural material strength are evaluated. Several options for superconducting materials are considered. For relatively low-field ( < 17 T) coils, NbTi and Nb3Sn are used. Both of these are commercially available and their properties are well understood. For higher magnet fields and operating temperatures, the ceramic oxide Bi-Sr-Ca-Cu-O is anticipated in the near term (within 5-10 years). Advanced structural materials are also considered. These include cryogenic steels, maraging steels, and titanium alloys. Of these, Incoloy 908 (a cryogenic steel) is found to be the most suitable material for a small SMES system. The impact of fiber-reinforced steel composites is also evaluated. It was found that each advance in materials technology will significantly impact the economics of 10 MWh SMES systems. If all advances become available (increased current density, operating temperature and allowed stress), the net conductor, structure and cryogenic cost may be reduced by over 45% relative to presently available technology. Further cost reductions result if novel approaches to magnet engineering are successful (e.g., force-reduced magnets).