b'33[W m-2]590N 4.5examines different wind farm sizes over Northa 4America, looking at the wake caused by the whole3.5wind farm, to answer questions such as what3happens to the wake length if wind farm size2.5increases, or how power extraction changes when a0 2farm is in the wake of another farm. Answers to these questions can help determine the optimal separation1.5between farms for greater energy. 1.590S 0.5Possner looked at the dynamics of ocean-based wind180 90W 0 90E -2 180 0farms and whether they could outperform land farms.90N [Wm ]Since wind speeds are higher on average over the60Nocean, ocean farms could theoretically intercept more energy. She investigated whether the open-ocean30Nwinds are faster because there is nothing to slow0them down and whether these farms would slow the winds similarly to land farms.30S60SPossner modeled the productivity of large Kansas90Swind farms compared to theoretical open-ocean180 150W 120W 90W 60W 30W 0 30E 60E 90E 120E 150E 180wind farms and found that the ocean-based farms could generate at least three times more power,0 8 16 24 32 40 48 56 64 72 80particularly in the North Atlantic. Drag from turbines would not slow ocean winds as much due to theAnna Possners wind power extraction study was a hypothetical, faster downward transport of momentum sustainedto get a sense of where in the worlds oceans the wind and by the land-sea contrast in surface temperature.circulation patterns could sustain the highest rates of energy extraction near the surface. As a first step, the researchers This tremendous ocean wind power is very seasonal,modeled turbines placed all over the globe, on land and sea, however. In the winter North Atlantic wind farmsat a density of one turbine per square kilometer. They ran could theoretically provide sufficient energy to meetsimulations that included the interaction of turbines, which substantially slows the winds and limited extraction to less than all of civilizations current needs. In the summer they5 watts per square meter (5 W/m 2 ) (top). If turbine density did could generate enough power for Europe, or thenot slow down the winds, they could achieve extraction rates of United States alone.up to 80 watts per square meter (80 W/m 2 ) (bottom). Note the different contour scales for each panel.Image courtesy Anna Possner'