Superconducting Generators May Enable Wind Turbines to Surpass 6 MW Limit

In a few blustery places, wind turbines are nearly cost competitive with conventional fossil energy, and tax credits designed to stimulate renewable energy growth are enabling profitable deployment of wind power in many parts of the country. West Texas, for example, is awash in wind turbines, like this majestic wind farm visible from I-20 near Loraine, TX.

Emerging Energy Research, an industry research firm, predicts that approximately $27 billion was spent on wind turbines in 2007, and over $55 billion is expected to be spent annually on this technology by 2015. With that kind of investment, a new approach is needed to enable wind energy to stand on its own and compete against fossil energy without artificial economic incentives (which will not last forever).

One approach to drive down cost has been to build bigger wind turbines. Among the largest turbines in the world is the 6 MW-peak E-126 built by Enercon (see: “Construction of world’s most powerful wind turbines in progress in Emden“), which sits on a gigantic 131-meter tower and has a mammoth rotor diameter of 126 meters. Wind turbines, however, cannot grow indefinitely due to practical limitations of physical size and weight. Components must be transported over roads or rails and 130+ meter towers must support the mass of generators in high winds.

To surpass the 6 MW practical wind turbine limit, a new technology is needed that can improve power output without increasing generator size and mass. Enter American Superconductor (AMSC), which is boldly synergizing this old energy technology (wind) with a new technology (superconducting wire). Using high-temperature superconducting (HTS) wire, which exceeds the current density of copper wire by 100 times, wind turbine power is increased without the size and weight penalties associated with scaling up conventional generators.

As reported in “NREL to validate 10-MW superconductor wind turbine,” AMSC announced an agreement with the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL) and its National Wind Technology Center (NWTC) to validate the economics of a 10 MW superconducting wind turbine. NWTC researchers will evaluate performance, manufacturing, and operating costs of AMSC’s 10 MW HTS wind turbine to estimate the actual cost of electricity generated by this system.

HTS wire has already seen a little action carrying current on the grid (see my blog posts: “2G YBCO Superconducting Wire May Improve Grid Security” and “Superpower’s 2-G Superconducting Cable Slated For Grid Installation“). However, this AMSC-DOE partnership represents a pioneering attempt to contain wind turbine size by deploying superconducting wire technology in generators. A company press release, “AMSC and U.S. Department of Energy Agree to Collaborate on 10 Megawatt-Class Superconductor Wind Turbines,” give more details: “superconductor technology will enable a 10 MW-class generator system that would weigh approximately 120 metric tons, compared with approximately 300 metric tons for conventional direct drive generators with this power rating.”

While their approach shows promise to make wind turbines cost competitive with fossil fuels, AMSC has some technical hurdles to overcome. According to “Superconductors to boost wind power” in Physics Today magazine, HTC wire is still very expensive. To compete with conventional copper, HTS wire needs to fall from $100/kA·m (achieved in low production volumes) to $15-$30/kA·m. Moreover, unique to superconducting wind turbines are maintenance and operating costs for cryogenic equipment to cool HTS wire below its critical temperature. These costs are not present in conventional wind generators.