The West of Duddon Sands project, around 12 miles off Barrow-in-Furness, has 42 of the proposed 108 turbines installed across the 25 square miles site. Now four turbines have started producing energy which is being exported to the national grid.
Once the wind farm is fully operational, expected to be later this year, it will be capable of generating 389 megawatts of electricity - enough to power around 280,000 homes.
Much of the design and planning work for the development was done by ScottishPower Renewables workers based in Glasgow.
Keith Anderson, chief executive of ScottishPower Renewables said: "Constructing an offshore wind farm is a major engineering challenge, and it is fantastic to see all of the different elements of the project coming together to achieve first power."
Around 1000 people are working on West of Duddon Sands, in areas ranging from electrical engineering and construction to marine biology.
Mr Anderson said he was delighted with the progress on the project and hailed the use of a £50 million purpose-built offshore wind terminal at Belfast Harbour, where components can be pre-assembled, as being particularly useful.
He added: "The new development at Belfast Harbour has also been crucial in the progress of the project. The investment in this bespoke facility is a major step forward for the offshore wind industry, and we hope it will act as a blueprint for similar projects at other locations around the UK.
"First power is a significant milestone for West of Duddon Sands, especially given the challenging weather conditions we have seen in recent months, and it gives us confidence that we will be able to fully complete the project later this year."