The German company will also provide an offshore substation for the wind farm, which will located 20 kilometres off Nantucket, at Horseshoe Shoal in the Nantucket Sound.
Siemens has subcontracted manufacturing of the substation to construction company Cianbro. This will be made in its facility in Brewer, Maine.
Construction began on Cape Wind just before the end of 2013 making the project likely to qualify for the investment and production tax credits deadlines on 1 January 2014.
Danish pension fund PensionDanmark’s $200 million loan it has offered Cape Wind is dependent on the project obtaining tax credit support.
The deal between Cape Wind and Siemens also includes a 15-year service agreement covering both the turbines and the substation.