Superconductive Magnetic Energy Storage (SMES) System Studies for Electrical Utility at Wisconsin

Two-layer low aspect ratio rippled and non-rippled solenoids mounted in surface trenches are described for superconductive magnetic energy storage utility applications. Open pool cooling in superfluid helium provides extended time cryogenic stability. Axial structure also functions as a protective heat absorbing secondary during emergency discharge. The cost of the conductor, trench, dewar, struts, radial structure, plus others are proportional to E^ 2/3 where E= stored energy; the cost of the axial structure is approximately E; and the cost of refrigeration is a constant plus an E^2/3 term. Costs scale approximately from E^0.58 (low E) to E^0.71 (100 - 3000 MWh) to E ^0.78 (3000 to 10,000 MWh). The cost of the ac-dc conversion system is about $60/kW. The electrical usage is best for load-leveling units that charge 8 h at night and discharge 15 h during the daytime. 98% storage efficiency and rapid power reversal are the two primary benefits of SMES. The potential impact of high Tc oxide superconductors is a 10%-20% cost reduction for large SMES units (above 3000 MWh). The operational storage efficiency of smaller units would improve to better than 95% for E > 10 MWh