Wind Wakes

clipped from www.popsci.com Turbine Contrails: Clouds form in the wake of the front row of wind turbines at the Horns Rev offshore wind farm near Denmark.  Aeolus Clouds stream in the wake of wind turbines arrayed at the Horns Rev offshore wind farm in this stunning photo. But David MacKay, a physicist at the University of Cambridge in the UK, sees the image as illustrating the common problem of back-row wind turbines losing power relative to the front row. Downstream wind turbines may lose 20 percent or even 30 percent of their power compared to their fellows in front, according to a study on wake effects at Horns Rev that MacKay highlights on his blog. The paper also emphasizes that different wind directions make it practically impossible to gauge an overall "steady state" for large wind farms, unless researchers can sample wind speeds and directions at multiple points throughout the array.