Spurred by the impending expiration of a federal tax credit that could be worth $780 million,Cape Wind, the long-sought giant wind farm off the Massachusetts coast, is apparently now under construction. It’s the first major offshore wind farm to begin construction in the United States, but its long-term fate hardly seems a done deal.

Cape Wind, the proposed $2.6 billion wind farm off the coast of Massachusetts criticized by local residents including the Kennedy family, will qualify for a key federal tax credit that expires at the end of the year, according to its turbine supplier Siemens AG. (SIE). Construction of some components has already begun, meeting the requirements for the investment tax credit, said Markus Tacke, chief executive officer of Siemens Energy’s wind power division.