But the wind industry is on the verge an even bigger shift, a step change ahead in power, efficiency and cost. Those 2.5-megawatt turbines still have traditional gearing mechanisms. Wind’s innovators want to free turbine motors from the burden of gears with the simplicity of direct drive.
"In a gear-driven system, you have three stages of gears, and each stage has multiple bearings and a structure to house all of these gears," Sandy Butterfield, the former Chief Engineer of the National Wind Technology Center (NWTC) at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) said at a recent wind industry conference. "We want to take a 15 RPM input shaft and spin it up to 1800 RPMs on the high speed side…[an] almost 100-to-1 ratio that requires multiple stages of gears, so a very complicated, high-precision machining, lots of close tolerances."
Butterfield understands the complexities involved better than almost anybody. He studied wind at NREL for 24 years and headed wind research there for the last eleven years in which wind technology went from farm-scale to utility-scale.
"A direct drive system eliminates all the gears," Buttefield explained. "Now you’re reduced to only two bearings or maybe one bearing that supports a large diameter rotor…and that’s it. So you have literally one moving part — the rotor. So just from a parts-number-count standpoint, you have a much more reliable machine."
The wind industry has barely begun to introduce direct drive innovation but there are glimmerings of the coming revolution. ENERCON was among the first with big direct drive turbines and the company is this year previewing its E82/3MW, a 3-megawatt version (enough power for 720 homes).
Siemens, one of the world’s leading wind machine makers, installed a prototype of its direct drive SWT-3.0-101 turbine in 2009 and brought it to market this month. Siemens promises its turbine will be more efficient and generate electricity even in low wind conditions. In addition, its nacelle’s dimensions (~22 feet in length, ~14 feet in width, 73 tons) allow it to be transported with the same vehicles used for Siemens’ less powerful 2.3 megawatt machine. GE is reported to be working on a similar concept.
Those are also the qualities Sandy Butterfield intends to design into the turbine his startup Boulder Wind Power company will build and market. He believes his design will lead to turbines light enough and less expensive enough to compete with gear driven systems. (Editor’s note: VCs have recently begun to plunk more money into wind, which still produces the lion’s share of renewable power not including hydroelectric dams.) Other companies are working on similar turbines; shown is an image of an MTorres turbine.
The advent of the Boulder Wind Power breakthrough technology and other 3-megawatt direct drive machines may have been hastened by the recession. The market was slowing just as Butterfield and others began working to get in, and Butterfield found that top talent became available just when he began looking for people. Money was not a problem, either. "What I’ve found is that there is money for a good idea," Butterfield said.
The direct drive turbine will completely change turbine maintenance issues for the better. Butterfield believes that his dedicated study of turbine technology is finally about to pay off in a wind machine less vulnerable to breakdowns. "We’ve been breaking gearboxes for 30 years and really never understood why it is so challenging," he said. If his concept eliminates such breakdowns, it will pay off for wind project developers, too.
The direct drive will also make wind turbines safer. One of the challenges the wind industry is currently beginning to widely confront is the compromised safety of doing maintenance and repair work in the tight quarters of the one-car-garage-sized box at the top of the turbine tower called the nacelle. It houses the thousands of mechanical and electrical parts that turn wind captured by the blades into electricity. With a direct drive, because of the use of permanent magnets instead of copper coils, there will be more space to work in the nacelle.
Finally, the direct drive will make wind power’s move to offshore production less costly. As Europeans already know and the U.S. energy community has begun to realize, the biggest future for wind is offshore. Winds blow hard and consistently over the ocean and can be captured immediately adjacent to large population centers.
Clear federal laws and regulations on offshore development were recently announced by the Department of the Interior. They will leave offshore wind and transmission projects vulnerable only to the more readily surmountable obstacles of nature (as opposed to the conundrums created by humans that continue to stymie onshore projects).
"When you’re offshore, you only want to have the most reliable machine you possibly can because the costs to access the machine are pretty high and if you can keep the components in sizes that you can easily manipulate from within the nacelle, that’s also a good thing. All of those things are possible in this particular technology," Butterfield said.
By Herman K. Trabish, www.greentechmedia.com