The 468MW Cape Wind project, of the coast of Massachusetts, has been a long-running saga in terms of gaining approval from the state authorities and battles between supporters and opposition groups since it was proposed in 2000.
The project still requires formal federal approval and the announcement of both the deal, and Siemens' plans to open what will become an offshore facility in Boston, may well have an influence on the approval process.
The final decision on Cape Wind is set to be made at the end of the month.
Speaking about the timing of the announcement a Cape Wind spokesman said it had been spending a lot of time making the decision so "why wait" [for formal approval].
The deal will be a disappointment to both Vestas and GE, which have both made a substantial effort to pick up the contract. In the event Cape Wind said the decision was between Siemens and Vestas.
In the event Cape Wind seems to have gone for Siemens as the ‘safe option' and described the Siemens 3.6MW as the ‘workhorse' of offshore wind power.
Speaking about the decision Cape Wind vice president Jim Gordon said: "We are pleased to be working with Siemens which is a market leader in offshore wind and we are thrilled Siemens is bringing clean energy jobs to Massachusetts by opening up its U.S. Offshore Wind office in Boston.
"This agreement between Cape Wind and Siemens represents a major step forward to jumpstarting the American offshore wind industry and increasing energy independence, creating a healthier environment while producing hundreds of green energy jobs."
The project has largely been stalled by environmentalists but has also faced opposition from some high profile players including the late senator Ted Kennedy (see 'Elitist Nimbyism').
The most recent attempt to derail the project was a claim by a North American Indian tribe who claimed the wind farm would impinge on a centuries old ritual of watching the sunrise over Nantucket Sound.
Last month, US interior secretary Ken Salazar stepped in an attempt to bring the rival for-and-against factions together to form an agreement.
The Cape Wind announcement follows yesterday's setback for Deepwater Wind's attempt to build the first US offshore wind project off Rhode Island.
A PPA for an initial 20MW trial project (the eventual project would have a 400MW capacity) was rejected by the states Public Utilities Commission.