Here’s a fly in the direct-drive ointment. China has been the world’s largest supplier of rare-earth materials, those used in high flux permanent magnets needed for direct-drive generators. The nation recently curbed production of the materials, most likely for its own use. China had supplied more than 90% of global rare earths, a group of 17 elements used in electronic technologies from electric motors to sonar systems. The country imposed controls on mining and exports after more than a decade of extraction depleted the resources and harmed its environment.
Turbine OEM Siemens, however, would like to develop supplies for rare earths in Australia, Russia, Greenland, and California to limit price increases and keep materials flowing to their products. Siemens Wind CTO Henrik Stiesdal says his company is developing a variant that uses no rare earth magnets at all. Siemens recently installed a 6-MW prototype direct-drive machine. According to Stiesdal, the company will offer geared turbines through 2015 as it transitions its products to all direct-drive technology.
In contrast, Vestas makes geared wind turbines with generators that the require only 10% of the material used in other direct-drive machines. So the generators do not depend heavily on the rare earths from China, according to the head of Vestas R&D Finn Stroem Madsen. “We will not deliver a technology that depends on a strategic raw material, such as the rare earths,” he says.
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