In September, the Advanced Research Projects Agency for Energy (ARPA-E) awarded US $31.6 million in grants to groups looking for alternatives to rare earth materials, which are critical to energy technologies. Two of those groups are trying to develop next-generation superconducting wire that can replace rare earth permanent magnets in the rotors of wind turbines. This research could lead to smaller, lighter, and more-powerful rotors that could enable giant offshore wind turbines capable of generating 10 megawatts of power each.
Despite their name, rare earth elements are not particularly rare in the Earth’s crust. They have become more scarce only since most companies mining them closed down their rare earth mines decades ago because of pollution and unprofitability, leaving Chinese mining companies with a near monopoly. When China began reducing its exports of rare earth minerals in 2009, industrial companies around the world began to worry. They feared that their ability to make a host of products, including electric motors in hybrid vehicles, disk drives, and compact fluorescent lighting, would be dramatically curtailed.
Among their many high-tech applications, rare earth elements are used to make powerful permanent magnets that generate magnetic fields inside turbine rotors. Generating the fields with coils of superconducting wire would let turbine makers do away with those large, heavy permanent magnets. That would allow wind companies to keep wind turbines at a reasonable size but get more power per tower.
The two research consortiums working on superconductor wire, led by materials scientists at the University of Houston and Brookhaven National Lab, in Upton, N.Y., have the same goal: to engineer a fourfold increase in the current-carrying capacity of their wire. Because a higher current would generate a more powerful magnetic field, such an advance would decrease the amount of superconducting wire needed in the rotor, which would cut down on cost.
Both groups include industry partners that have already cranked out state-of-the-art wire in significant quantities: The group from the University of Houston, headed by Venkat Selvamanickam, includes SuperPower of Schenectady, in New York, while the Brookhaven group (headed by Qiang Li) includes AMSC.
Selvamanickam’s team is working on ways to introduce nanoscale defects into the superconducting layer within the wire to “pin” the flux lines in place. This can be done by doping the material with other chemicals during the vapor-deposition process. The Brookhaven group is working to embed nanostructures within the superconducting material.
Neither group would disclose the full details of its approach, citing the proprietary nature of the technology.
But if these groups figure out how to uniformly distribute the flux-pinning structures and thus increase the amount of current that can flow through the wire, there will still be economic hurdles to overcome.