Northern wind: ScanWind has installed turbines along the Norwegian coast.
“Eliminating the gearbox from the wind turbine [removes] the technically most complicated part of the machine, inherently improving reliability,” says Henrik Stiesdal, chief technology officer of Siemens AG. Furthermore, if a permanent magnet is used in the generator, as is the case with newer turbines, the efficiency goes up even more. That’s because, unlike today’s electromagnetic generators, permanent magnets don’t need power.
Direct-drive generators currently cost more than geared systems and are 15 to 20 percent heavier. Still, GE’s decision to buy ScanWind is smart, says Butterfield. “Offshore machines are so expensive in terms of maintenance that some people are thinking the tradeoff tilts in favor of direct-drive generators,” he says. “I am optimistic that there is technology out there that’s going to help bring direct-drive generators down in parity with the weight and cost of geared systems.”
Siemens certainly believes so. The leader in offshore wind energy has been testing two 3.6-megawatt proof-of-concept direct-drive turbines near Denmark for over a year now. Stiesdal says that the technology has proven to work just as well as gearboxes in terms of power, vibrations, temperature, noise, and reliability. Now it’s a matter of bringing down its cost.
GE, meanwhile, expects to have a market-ready product by late 2012. It is targeting the European market initially because nearly all of the 1,473 megawatts of offshore wind power currently available come from installations along European coasts. According to industry analysts, this capacity must reach 30,000 megawatts by 2020 if the European Union is to meet its renewable-energy targets. One of the reasons for choosing ScanWind, says GE, is because of the company’s footprint in the Nordic countries, which, along with the U.K. and Germany, are the brightest spots for offshore wind energy.