Siemens will test two 3.6-megawatt (MW) wind turbines with direct drive (DD) technology at a site in west Denmark. The company 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. 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.

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.

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 2500 kNm the two generators are among the largest permanent magnet machines ever built anywhere in the world.”