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Germany's Enercon, which has been building a reputation for protracted legal battles over wind technology patents, has concluded a voluntary patent sale entirely separate from its long running disputes with Vestas. An agreement announced last year is now finalised between Enercon and Maxwell Technologies in the United States over the use of ultracapacitors as a power source for blade pitch systems.

San Diego-based Maxwell says this opens the door for its products into a market comprising around 70% of the world's wind turbines. The company has sold ultracapacitors to Germany's Enercon, the world's third-largest turbine manufacturer, since 2004. But Enercon owns worldwide rights to use ultracapacitors as a backup source for momentary power supply to blade pitch systems. Maxwell, which has sold hundreds of thousands of ultracapacitors to Enercon, is now looking to expand its market reach.

"We've been contacting all of the other wind turbine manufacturers," says Maxwell's Michael Sund. "Our thrust since summer has been to line up business with electric blade pitch system makers other than Enercon."

Vestas, which supplies roughly 25-30% of the world's turbines, is alone in using a hydraulic blade pitch system, according to Sund. That leaves 70-75% of the global market to either use batteries or ultracapacitors. Two German companies, turbine maker Vensys and power drive component supplier LTi ReEnergy, are among the companies that have become new Maxwell customers, designing ultracapacitors into their pitch systems in recent months.

"The beauty of an ultracapacitor in this backup power role is that it should be maintenance-free for the life of the turbine," Sund says. "It charges off the wind system and can sit there, fully charged and standing by until it's called on to do its thing."

Any turbine maker that buys Maxwell ultracapacitors for its blade pitch systems is under the umbrella of the license agreement and so does not contravene the Enercon patent. And, says Sund, while other companies are free to make ultracapacitors, they have no such rights. Lead-acid batteries, a common alternative, are relatively inexpensive up front but have inherent and expensive limitations, such as requiring regular maintenance and periodic replacement. Enercon turbines use anywhere from two to 800 flashlight-battery-sized ultracapacitors mounted on circuit boards in a design that Enercon came up with for its own use. But the company does not make ultracapacitors.

"Enercon was the early adopter and they did a lot of the design work and validation and now there's kind of a track record," Sund says. "We think ultracapacitors are going to play an increasing role in the industry. Now that we've made an investment in the license we're definitely looking for a return on that investment. But it's only worth it to us if we sell more ultracapacitors." The two companies have agreed not to disclose terms of the licence.