The £1.6 billion project will consist of 108 Siemens 3.6MW turbines and will be among the largest offshore wind farms in the world at the time of commissioning in 2014.
ScottishPower Renewables chief executive Keith Anderson said: "West of Duddon Sands will be the first offshore wind project in our pipeline to be commissioned, and marks the start of our extensive investment programme in the offshore wind sector.
"We've been working with DONG on this project for many years now and we look forward to continuing this partnership throughout the construction and the operation of the windfarm."
West of Duddon Sands will be adjoin DONG Energy's Walney 1 and 2 wind farms. These two wind farms will be commissioned in 2011 and have a total capacity of 367MW.
