The 389MW project had produced a load factor of 47.7%, said the developer, 15% over budget during the first six months of 2015. The project added €73.8 million to the gross margin in H1.
West of Duddon Sands wind farm is in its first full operating year, and was developed as part of a joint venture with Dong Energy.
Iberdrola's renewables business' pre-tax earnings increased 18.9% in the period to €824.2 million. As well as the improved output of West of Duddon Sands, Iberdrola said the increase was helped by a recovery of prices in Spain, after an exceptionally low corresponding period in 2014, and a stronger euro against the US dollar.
West of Duddon Sands is Iberdrola's only current operating offshore project.
However, it is developing the 350MW Wikinger project in the German North Sea, which is due online by the end of 2017. It is also working on the 714MW East Anglia One project off the UK's east coast. A final investment decision on this project is expected in early 2016, following the award of a Contract for Difference subsidy by the UK government in February.
Iberdrola is also part of the Eole-RES consortium developing the 500MW Saint Brieuc project in France, which is still in the planning phase.