On a chilly June day, with the Massachusetts island of Martha’s Vineyard just over the distant horizon, a low-riding, green-hulled vessel finished hammering a steel column nearly 100 feet into the bottom of the Atlantic Ocean. This was the beginning of construction of the first giant wind farm off the United States coast, a project with the scale to make a large contribution to the Northeast power grid. For some of those looking on from a nearby boat, the driving in of the first piling marked a milestone they had labored to reach for two decades. The $4 billion project,...