[pagebreak:Unfurling Wind Power's Sails]
As a sailor, Mike Zuteck often had observed the way a sail rig twists in the wind. The motion sparked an idea for a new wind-turbine blade that could generate more energy in low-speed wind conditions.
“You learn something from making the boat move better with the wind,” said Zuteck, a wind-energy consultant based in Clear Lake, Texas, who has been racing sailboats since his days on the Massachusetts Institute of Technology’s sailing team in the 1960s. “It’s a thinking you pick up from observing the wind move."
The fiberglass-and-epoxy-resin blade looks like a carving knife that has been curved – or swept – near the tip. The so-called “sweep twist” blade was designed to be more attuned to wind's natural movement, potentially producing more energy in low wind and reducing fatigue loads, or wear and tear, on the blade.
Knight & Carver, which is designing and making the blade, expects to commercialize it later this year. The company hopes the blade will open slower-wind regions currently closed to wind-energy production. The company expects the technology to capture 5 to 10 percent more energy in regions with low wind speeds.
Such regions, which have an average wind speed of 5.8 meters per second, measured at a height of 10 meters, are so abundant in the United States that the technology could increase by twentyfold the amount of land that can be used to generate wind energy, according to Sandia National Laboratories, which have tested prototypes.
Because slower wind regions often are near areas where power is already loaded onto the grid today, such as in the Midwest, the blade also could reduce the cost of transmission, said Gary Kanaby, director of business development for Knight & Carver.
Tom Ashwill, who leads Sandia’s blade research in Albuquerque, N.M, said the blades will cost about 10 percent more than traditional blades. That might not sound so enticing, but it means existing wind farms with 750-kilowatt turbines that were popular in the 1990s could increase electricity generation just by replacing their worn blades, without having to add more turbines. Knight & Carver plans to target that market initially for retrofitting.
And because blades make up only about 15 percent of the total turbine cost, according to Ashwill, the new and improved blade would increase the overall cost by only 1.5 percent more, making them more cost effective overall.
The idea has gained recognition.
At WindPower 2008 in June, the project was selected as one of the U.S. Department of Energy's top 10 program accomplishments. Knight & Carver also raised $12.5 million in its first round of funding from the Global Environment Fund earlier this year.
Maureen Hand, a senior engineer with the National Renewable Energy Laboratory's National Wind Technology Center in Golden, Colo., called the project “unique,” especially in an environment of rising wind-turbine costs.
“Any increase in energy capture will deliver cost savings and have a positive impact on the industry,” she said.
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From Yachts to Wind Power
Zuteck, who began designing wind blades for NASA in the 1980s, first proposed the idea in 2002, when the U.S Department of Energy and National Renewable Energy Laboratory began offering grants for innovative blades.
National City, Calif.-based yacht builder Knight & Carver had entered the wind-turbine repair and maintenance business in 1997, when a small wind farm asked if the company could use its experience with composite materials to help resolve some structural issues it was having with its blades. This success resulted in the establishment of a subsidiary, San Diego-based Knight & Carver Wind Group.
With its experience servicing turbines, the group knew that blades for the 750-kilowatt turbines built in the 1990s would soon be coming up for replacement. Knight & Carver was eager to take advantage of what it saw as a lucrative new market for the large blades.
The company heard about Zuteck’s idea and put together a team of engineers to collaborate with the inventor and submitted a proposal for what it calls the sweep twist adaptive rotor – or STAR – blade.
The project – which received a grant of $2 million, combined with $800,000 of funding from Knight & Carver – ended up making a blade that stands 27.1 meters (about 88.9 feet) long. That’s almost 3 meters (9.8 feet) longer than the older blades they are intended to replace, Ashwill said.
DOE labs are still testing the blades, but Knight & Carver hopes to commercialize the blade in the fall and it could head in several different directions: license its technology to big blade manufacturers, partner with a turbine manufacturer or manufacture the blades itself.
The company is keeping an open mind, Kanaby said.
But Ashwill said it could take another year for the blades to become commercially viable.
“This is an experimental blade, a fairly new use of this concept, so even with the statistics, how it performs eventually [remains to be seen],” he said. “Whoever adapts this technology will have to move to a prototype with one or two more modifications at the next stage.”
Zuteck said the 750-kilowatt turbines are not ideal for low-wind areas. “Low-wind speed sites typically have a lot of wind sheer and you will need taller towers, so the 750-kilowatt turbine will not be the right size for low-wind areas, except perhaps in rugged terrains where it is hard to get the bigger turbines in,” he said.
A longer blade designed for today’s 1.5- to 2.5-megawatt turbines would be more suitable for low-wind areas, according to both Ashwill and Zuteck. But one obstacle is that a longer blade would require more stiffness to keep it from wearing down sooner.
Carbon fiber would help increase stiffness, but the material is expensive and in short supply, as well as vulnerable to lightning, Ashwill said.