A multimegawatt Danotek generator undergoes tests in their facility in Canton, Mich.

A manufacturer of permanent magnet (PM) generators and power converters for the wind energy market, says it will be expanding its portfolio with the addition of large PM generators for low- to medium-speed applications primarily intended to meet the growing market for offshore wind turbines with rated outputs within the range of 6 to 8 MW.

The 7-MW PM generator class builds on the foundations laid by the company’s existing range of medium and high-speed generators for onshore installations. By scaling up existing designs that are already in advanced development or early production, Danotek says it can offer wind turbine OEMs, prototype systems optimized to their requirements within 12 months. Both direct drive and medium-speed drivetrains are applicable to offshore installations, the preferred solution being a compromise to the often divergent goals of maximizing reliability (by simplifying gearbox design), minimizing weight, increasing efficiency, and maintaining a low capital cost. Direct drive, low-speed PM generators are physically much larger but allow a less complex drivetrain by removing the need for a gearbox. A single or two-stage gearbox with a medium-speed PM generator is said to deliver a highly reliable drivetrain without incurring the significant additional weight and costs associated with large diameter, direct-drive generators. Danotek’s new product family will be able to scale direct drive and medium-speed drivetrains.

The offshore wind market has been steadily growing globally. From today’s installed base of 4.1 GW, offshore wind is forecast to grow at a CAGR of more than 60% to exceed 70 GW by 2017 (Pike Research, 2011, Global Wind Energy Outlook Report). Growth in offshore wind is primarily driven by increasing demand in Europe and Asia. One of the challenges facing developers of offshore wind projects is the reliability of the wind turbine drivetrain. Traditional double-fed induction generators (DFIG) have the disadvantage of requiring extensive, and potentially expensive, routine servicing of the brush gear and slip-rings. PM generators completely avoid this maintenance headache.

In June 2011, a consortium led by the National Renewable Energy Laboratory (NREL) that includes Danotek, was one of six groups selected for an award by the Department of Energy (DOE) to advance next-generation designs for wind turbine drivetrains. The project will focus on reducing the cost of wind energy by optimization of the wind turbine drivetrain, with technology developed being scalable to drivetrains of 10 MW or more. Commenting on the programs’ synergies, says Danotek CEO Don Naab said “We anticipate leveraging knowledge gained from the DOE program to enhance and accelerate our 7 MW offshore generator program.”

Danotek Motion Technologies
www.danotekmotion.com