Wind direction variation with height (wind veer) plays an essential role in the inflow wind field as the wind turbine enlarges. We explore the wind veer characteristics and their impact on turbine performance using a 5-year field dataset measured at the Eolos Wind Energy Research Station of the University of Minnesota. Wind veer exhibits an appreciable diurnal variation that veering and backing winds tend to occur during nighttime and daytime, respectively. We further propose to divide the wind veer conditions into four scenarios based on their changes in turbine upper and lower rotors that influence the loading on different rotor sections: VV (upper rotor: veering, lower rotor: veering), VB (upper rotor: veering, lower rotor: backing), BV (upper rotor: backing, lower rotor: veering), and BB (upper rotor: backing, lower rotor: backing). Such a division allows us to elucidate better the impact of wind veer on turbine power generation. The clockwise-rotating turbines tend to yield substantial power losses in scenarios VV and VB and small power gains in scenarios BV and BB. The counterclockwise-rotating turbines follow exactly opposite trends to the clockwise turbine. The derived findings are generalizable to other wind sites for power evaluation and provide insights into the turbine type selections targeting the maximum profits.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation CAREER award (Grant No. NSF-CBET-1454259), Xcel Energy through the Renewable Development Fund (Grant No. RD4-13), and IonE of the University of Minnesota. The authors thank the engineers from St. Anthony Falls Laboratory, including Christopher Milliren, Chris Feist, and Matthew Lueker, for the fruitful discussion regarding the Eolos database.