The Block Island Wind Farm off Rhode Island nears completion and will be the first ever offshore wind farm in the U.S. Essentially, it’s a test site, just 30 MW. However, if all goes well – and let’s hope it does – developer Deepwater Wind plans a South Fork, a 90 MW wind farm 30 miles from Long Island and Deepwater One, a 1,000 MW wind farm off Martha’s Vineyard. (Presuming of course that squealing NIMBYs like the Kennedy clan, proud environmentalists all, don’t again succeed in killing offshore wind anywhere they can possibly see it.)
Wired details the engineering challenges:
The blades on Deepwater Wind’s turbines will be almost 250 feet long. That means the top and the bottom of the rotors will be separated by 500 feet or more. Anything covering that much area will have to deal with widely variable wind conditions. Sometimes the wind will be the same speed across the whole turbine, but that speed will change dramatically over the course of the day. Other times, the winds can be steadily 10 miles per hour faster at the top than at the bottom.
To help protect the turbines’ machinery and electronics, engineers can lock their rotors to keep them from spinning too fast or chaotically. “If we reach some level of wind which is not acceptable, then we stop the machine and the machine is put in standby.” The same happens if it gets too cold.
But stopping the rotors doesn’t stop the wind. The surface area of each blade is about the same as a football field, so there’s a lot of air hitting the turbine and trying to topple it. To stay steady, turbines are anchored to the seafloor and to a narrow foundation dug 200 feet underground.