(May 2008) Senators were voting on legislation to extend the renewable production tax credit (PTC) as this issue of Fortnightly went to press. But with federal tax support for...
In the Mainstream: Wind Turbines Take Off
New technologies are helping windpower mature as a viable power supply choice for utilities.
global weather conditions, going back 57 years in some locations. Additionally, they incorporate topographic and surface features to further refine wind-resource simulations.
WindLogics was engaged by Xcel Energy and the Minnesota Public Utilities Commission to model the state’s wind resources and analyze them in terms of hypothetical projects, including their effect on the transmission grid and their wholesale market implications. The model will simulate energy production on five-minute intervals at 152 points across the Minnesota landscape, as part of the state’s mandate to increase renewable energy’s market share to 20 percent of power consumed.
“To achieve such a high penetration of wind, you need to understand how higher percentages of renewable energy will impact the system,” Ahlstrom says. “We’re incorporating an AREVA grid-integration simulation, and we’ve had a lot of involvement with MISO [Midwest Independent Transmission System Operator]. It’s the most extensive combination of modeling ever done in the windpower industry.”
Innovations are emerging in less esoteric areas as well. In the aftermath of widespread durability problems involving large turbine gearboxes in the field, manufacturers have focused on hardening components and rethinking designs. “We believe the gearbox failures have occurred because as rotors scale up, RPMs slow down,” Dehlsen says. “That translates into much higher torque, and the industrial gearboxes have reached their limits.”
Clipper’s solution to this issue is to use a pair of massive bull gears, driving four sub-gear sets that drive separate permanent-magnet generators. A prototype of its 2.5-MW Liberty turbine, using such a design, is operating at a National Renewable Energy Laboratories site in Wyoming.
“Our drive train splits the load path 16 times in the first stage, whereas a conventional gearbox will split it about four times,” Dehlsen says. This dramatically reduces the forces applied to gear teeth, affording more generous structural margins and extending component longevity, while reducing gearbox mass. Furthermore, permanent-magnet generators save weight by eliminating the need for copper windings.
Other manufacturers also are developing unconventional approaches. Vensys, for example, is operating a prototype in Nova Scotia of a turbine that uses no gearbox at all, but instead directly drives a large permanent-magnet generator. Such developments are garnering a great deal of interest as manufacturers seek ways to improve efficiencies and reduce costs.
“A couple of years ago, watching newcomers in the field, we more or less laughed at them,” Aabo says. “But now it looks like they are getting into something, and some of these technologies might break through.”
Beyond Boom & Bust
Windpower often is touted as the world’s fastest-growing power-generation technology. And in the face of historic fuel-price peaks, policymakers are more eager than ever to propel windpower’s progress. As a result, the PTC seems likely to be renewed in Congress, and U.S. wind development will continue at a strong pace, even if structural factors constrain that growth.
“We are advocating a more stable and visible incentive for wind, because that’s the only way this industry will be able to achieve independence,” Gleitz says.
Moreover, for wind projects to attain strong economic fundamentals, the magnitude of incentives might need to increase