Siemens Energy has announced that it will test two 3.6 MW wind turbines with direct drive (DD) technology at a site in west Denmark.
The first test turbine has been erected, with the second to follow later in 2008. Siemens will subject the two DD wind turbines to comprehensive testing for a minimum of two years.
“The purpose of this project is to assess whether direct drive technology is competitive with geared machines for large turbines,” a company spokesman said.
“Beside testing DD technology, Siemens will continue product development of turbines with gearboxes, and new turbines featuring geared technology will be released in the upcoming years.”
 Wind power business is one of the major contributors to the Siemens environmental portfolio. In fiscal 2007, the company generated revenue totaling some 17 billion euros from products and solutions for environmental and climate protection.
The main advantage of direct drive wind turbines is their smart, straightforward design that makes the use of gearboxes dispensable. With fewer moving parts DD technology has the potential to reduce maintenance costs, which could result in higher turbine availability. However, DD machines are typically known to be heavier and more expensive in manufacturing than geared wind turbines. One of the main objectives of the Siemens DD project is to establish if and for which turbine sizes direct drive machines are competitive with geared turbines. A special focus will be on offshore applications, where wind turbines need to be especially robust and reliable.
Siemens will equip the two DD test wind turbines with synchronous generators excited by permanent magnets. The test generators will be supplied by two different companies: one was developed by the Siemens Industry Sector and the other by Converteam.
“By selecting two manufacturers we will be able to compare and access the benefits of different technical solutions with respect to generator design,” said Henrik Stiesdal, CTO of the Siemens Wind Power Business Unit. “At a nominal torque in the range of 2,500 kNm the two generators are among the largest permanent magnet machines ever built anywhere in the world.”