Effects of wind turbine wakes on micrometeorological conditions over a crop canopy

The U.S. Department of Energy (DOE) envisions wind power providing 20% of the electrical production in the United States by the year 2030. This complies with the DOE mission statement to “advance the national, economic, and energy security of the United States.” Meeting this demand will require additional wind turbine development on croplands in the Midwest where wind energy resources are favorable. Few studies have reported the influences of wind turbines and large wind farms on the crop microclimate. There are indications of the wind turbine wake turbulence changing sea surface roughness in the wake of offshore wind farms. The possibility exists that wind farms co-located with agricultural crops will influence the crop microclimate. This project seeks to describe and quantify this interaction. Eddy covariance flux towers were installed at locations 5 rotor diameters upwind and 2.5, 17, and 34 diameters downwind of one line of wind turbines in an Iowa wind farm. Near-surface temperature, humidity, wind, and surface fluxes above a maize canopy were collected with 5-min averaging during the summer of 2010. The analysis of these measurements for the period July 1-3 is reported. Preliminary results suggest that the vertical temperature difference above the crop at night is reduced by 0.4K in the turbine wake indicating less stable conditions in the turbine-perturbed flow. During the day the upwind vertical temperature difference is insignificant while for the downwind the difference is -0.2K and supports slightly unstable conditions. At the upwind tower, for this period, the turbulent intensity lacks diurnal variation, whereas at all downwind locations a 5% increase (decrease) during the day (night) was observed. Additional analysis of other variables (e.g. fluxes of CO2 and water vapor) will be used to assess the impacts of wind turbine turbulence on crop microclimate.