Floating Wind Turbines on the High Seas Could Produce Massive Amounts of Power

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 Monday 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 (1.2-1.8 miles) 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 Monday 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.

Possner and Caldeira credit this kinetic energy recharge to cyclonic weather systems that abound over the oceans in the mid-latitudes, forming as the seas release heat into the atmosphere.  Such weather can wreak havoc when they reach hurricane scale and come ashore—as Hurricane Maria has done to Puerto Rico and its power grid.

But for open ocean wind farms, those cyclonic storms should be a boon, promoting the mixing of kinetic energy between the boundary layer and the more powerful trade winds sailing over it.

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