|RAJEWSKI, DANIEL - Iowa State University|
|TAKLE, EUGENE - Iowa State University|
|LUNDQUIST, JULIE - University Of Colorado|
|SPOTH, KRISTOPHER - Iowa State University|
|DOORENBOS, RUSSELL - Iowa State University|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2014
Publication Date: 5/13/2014
Citation: Rajewski, D.A., Takle, E.S., Lundquist, J.K., Prueger, J.H., Pfeiffer, R.L., Hatfield, J.L., Spoth, K.K., Doorenbos, R.K. 2014. Changes in fluxes of heat, H2O, CO2 caused by a large wind farm. Agricultural and Forest Meteorology. 194:175-187.
Interpretive Summary: Wind turbines are becoming a common feature in many agricultural fields. This is particularly true in many areas of the corn belt in Iowa and other corn belt states. There has been interest in determining if wind turbine arrays (multiple turbines in straight lines) in production fields can affect corn/soybean yields. The interest centers on the question of whether the large wind turbine blades disrupt or enhance the natural exchange processes of carbon dioxide (CO2) and water vapor (H2O) gases (critical gases for plant growth) of corn and soybean fields. A study was conducted in 2010 and 2011 to measure carbon dioxide and water vapor exchange over a large Iowa corn field that contained multiple wind turbines in straight lines across the corn field. Ten-meter tall towers were located upwind and downwind of two lines of turbines. One tower was located in such a way that it was not influenced by any turbine. Heat, water vapor, and carbon dioxide were measured for two growing seasons. Results showed that when natural wind flow was perpendicular (southerly) or slightly oblique (southwesterly) to the row of turbines during the day, H2O was enhanced by a factor of five in the lee of the turbines as compared to a natural parallel flow to the turbine lines (west wind). Carbon dioxide was also enhanced but not as much as the water vapor. The enhanced exchange of CO2 and H2O suggests that wind turbines can potentially affect yields. The benefit of this research will be to corn and soybean producers in assessing future impacts (positive or negative) to yields from wind turbines.
Technical Abstract: The Crop Wind Energy Experiment (CWEX) provides a platform to investigate the effect of wind turbines and large wind farms on surface fluxes of momentum, heat, moisture and carbon dioxide (CO2). In 2010 and 2011, eddy covariance flux stations were installed between two lines of turbines at the southwest edge of a large Iowa wind farm from late June to early September. The stations report changes in fluxes of momentum, sensible heat, latent heat, and CO2 above a corn canopy after surface air had passed through a single line of turbines. In 2010, our flux stations were placed within a field with homogeneous land management practices. We stratify the data according to wind direction, diurnal condition, and turbine operational status. Within these categories, the downwind-upwind flux differences quantify turbine influences at the crop surface. Flux differences were negligible in both westerly wind conditions and when the turbines were non-operational. When the flow is perpendicular (southerly) or slightly oblique (southwesterly) to the row of turbines during the day, fluxes of CO2 and water (H2O) are enhanced by a factor of five in the lee of the turbines(from three to five turbine diameter distances downwind from the tower) as compared to a west wind. However, we observed a smaller CO2 flux increase of 30-40% for these same wind directions when the turbines are off. In the nighttime, there is strong statistical significance that turbine wakes enhance upward CO2 fluxes and entrain sensible heat toward the crop. The direction of the scalar flux perturbation seem closely associated to the differences in canopy friction velocity. Spectra and co-spectra of momentum components and co-spectra of heat also demonstrate nighttime influence of the wind turbine turbulence at the downwind station.