December 1, 2008

The return of the Clipper Liberty wind turbine

Drew Robb

Strong wind rising

If anything, the situation facing wind turbine builders may be more severe than what traditional power industry manufacturers have to deal with. After all, how often does an industrial turbine supplier release a new line of larger machines? The wind industry, on the other hand, ramps up its power output every couple of years. At the end of the nineties, turbines of 750 kW were the norm. They were replaced by 1.5-MW models, which became standard a few years ago. Now, models in the 2- to 3-MW range are beginning to dominate. Yet 3.5-MW and 5-MW gear is already running in the field, and companies have announced 6- and 7.5-MW models as being in the pipeline.

"The wind industry is continually pushing the envelope and extending the capabilities of the entire supply chain as it expands," said Maurer. "At each stage, gearbox and blade manufacturers are forced to provide parts that go beyond the bounds of current technology. In many cases they are also forced to build new facilities and new equipment to manufacture parts that are larger than those demanded by any other industry."

Every new generation of turbine requires a complete redesign, as you are moving into a whole different level of stress and strain within the turbine. The market demands more capacity while at the same time it insists upon a lower cost for wind energy. So if you have a blade that produces 10% more energy, then that larger blade has to cost less than the gain it provides.

"If it’s proportionate, then there is no reason to build the larger machine," said Maurer. "Every step of the way, therefore, you have to push the technology forward while keeping it cost-effective. If you don’t experience any issues at all, it is probably the case that the machine has been overdesigned and therefore is too expensive. Product design is a delicate balance of robustness and cost-competitiveness."

For Clipper, though, this not only meant bringing a new turbine onto the market but also establishing a manufacturing plant in Iowa from scratch. The 2.5-MW Clipper Liberty, the largest wind turbine made in the U.S., has rotor diameters ranging from 89 meters (292 ft) to 100 meters (328 ft). It includes features such as variable-speed technology, low-voltage ride-through, and four MegaFlux permanent magnet generators — a departure from previous models deployed since the modern wind energy industry began in the early 1980s.

In early 2007, with growing sales orders and more on the horizon, Clipper ramped up operations significantly, increasing its plant floor space from 215,000 to 330,000 square feet and its plant workforce from 154 to 297. The ISO 9001:2000 Quality Management System was used to maintain a high standard in the turbines produced. Despite these processes, its first production machines experienced the above-noted teething pains.