Superconducting magnetic energy storage (SMES) is a promising technology for electric utility stabilization of transmission, load compensation, and frequency regulation. This paper presents the results of a study to reduce the capital cost of an SMES system. The study focused on a toroidal-shaped superconducting coil system and concerned both 100MW/15kWh SMES for stabilization on transmission and 100MW/500kWh SMES for load compensation and frequency regulation. The charge/discharge ratio (k) was optimized in consideration of the economical efficiency of the whole SMES system, and thereby k=0.52 for small-scale SMES and k=0.86 for medium-scale SMES were obtained. To reduce the cost of a superconducting coil system, the system's design should be based on the concepts of a compact, a simple structure and small material amount. The aspect ratio of a toroidal coil system and that of a solenoid unit coil are determined from the viewpoints of minimum material amount. Aluminum-stabilized forced-flow superconductors have been newly proposed to achieve high voltage and high magnetic-field design in correspondence with small coils and reduced coil-turn numbers. New oxidization techniques for the aluminum surface of the stabilizer have been developed and the structure of the superconductor is designed simply and symmetrically to reduce manufacturing cost and ac loss. The supercondutor's favorable performances have been confirmed through short sample tests. These results provide a strong incentive for utilities to encourage and support the development of SMES cost-reduction technology.
