Gunfleet Sands III is part of Dong Energy's 172MW Gunfleet Sands North Sea wind farm. The turbines will be tested for the next three years at the site.
UK minister for climate change Greg Barker officially opened Gunfleet Sands III today.
Henrik Stiesdal, Siemens Wind Power chief technology officer, said: "Gunfleet Sands III is a very important project for us to bring the 6MW direct drive turbine out to the offshore environment.
"The two prototypes have been pre-tested here under hardest conditions and we have made tremendous progress with the experiences gained by that. Now we will test the turbines under long-term conditions of normal energy production."
The turbines have been tested onshore at the Høvsøre and Osterild test centres in Denmark, and the Gunfleet Sands tests will determine the roll-out of the 6MW machine at future Dong Energy projects in the UK.
Dong Energy signed an agreement with Siemens to deliver 300 6MW turbines for use at its projects in the UK in July 2012, and for 154 6MW turbines at its German Gode Wind projects from 2015.