Rapid discharge makes SMES attractive for quickly stabilizing high-voltage transmission lines during periods of heavy use. Crucially, ABB is developing electrical switches that would allow SMES systems to release their energy gradually, over up to an hour, to help compensate for drops in output from renewable energy sources such as wind and solar.

Luongo says that to compete with lead-acid batteries and other technologies, SMES systems may need to be significantly larger than the 1-to-2-megawatt-hour devices envisioned by ABB. They may need to offer tens of megawatt hours of storage, Luongo says, "and the cheaper the other technologies get, the farther out that crossover point gets."

Steven Minnihan, an analyst at Lux Research, says SMES devices should last longer than flywheels or batteries, because they have no moving parts. But, he says, the material costs remain high. "The real benefit is its substantial life over batteries and flywheels, but I don't think it's the most cost-effective technology," Minnihan says.

SMES systems have about the same life expectancy as pumped hydro and compressed air systems: 10-20 years, as opposed to 1-10 years for batteries and 8-12 years for flywheels, Minnihan says. He has reservations about ABB's approach because it requires large quantities of high-temperature superconducting wires that at today's prices would make grid-scale SMES systems prohibitively expensive.

Although the cost of superconducting wire has dropped significantly in recent years, Ramanan admits that it would need to fall by another 300 percent for SMES to be competitive with other grid-scale energy-storage technologies. He says reducing wire cost is a significant technical challenge but adds that taking on such challenges is the purpose of projects funded by ARPA-E. "If we didn't think this had potential, we would not have gone after this," he says.