The world’s first offshore wind farm employing floating turbines is taking shape 25 kilometers off the Scottish coast and expected to begin operating by the end of this year. New research by atmospheric scientists at the Carnegie Institution for Science in Stanford, Calif. suggests that the ultimate destination for such floating wind farms could be hundreds of kilometers out in the open ocean. The simulations, published today in the Proceedings of the National Academy of Sciences, show that winds over the open ocean have far greater staying power than those over land.
Wind power generation is obviously contingent on how fast and how often winds blow. But only over the past decade have scientists and wind farm developers recognized that the winds measured prior to erecting turbines may not endure. For one thing, dense arrays of wind turbines act as a drag on the wind, depleting local or even regional wind resources.
It is now generally accepted that drag from wind turbines in the boundary layer (where the atmosphere interacts with Earth’s surface) limits the kinetic energy that large land-based wind farms can extract to about 1.5 megawatts per square kilometer (MW/km2). “If your average turbine extracts 2-6 MW, you really need to space those turbines 2-3 kilometers apart because the atmosphere just doesn’t give you more kinetic energy to extract,” says Carnegie postdoctoral researcher Anna Possner.
What Possner and climate scientist Ken Caldeira reveal today is that the atmosphere is more generous out in the open ocean. There, they estimate, wind farms could be packed more tightly, because energy should flow down from above the boundary layer to quickly restore winds depleted by wind turbine rotors. In some regions, such as the North Atlantic, the simulations suggest that large wind farms can extract 6 MW/km2 or more.