The approval was formally announced by interior secretary Ken Salazar. He said the government had evaluated any potential impacts on the "environmental and cultural resources of Nantucket Sound".
The project’s 130 Siemens 3.6MW turbines will have a nameplate capacity of 468MW and are expected to have an average output of 182MW.
According to the interior department, construction could begin this year. However, Cape Wind only has a PPA for half of the project.
In October, Cape Wind Associates Salazar signed a 28-year agreement, leasing the company 25 square miles of the outer continental shelf in Nantucket Sound, Massachusetts.