Location: Soil, Water & Air Resources ResearchTitle: Crop/Wind-energy Experiment (CWEX): Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm Author
Submitted to: Bulletin of the American Meterological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2012
Publication Date: 5/10/2013
Citation: Rajewski, D.A., Takle, E.S., Lundquist, J.K., Oncley, S., Prueger, J.H., Horst, T.W., Rhodes, M.E., Pfeiffer, R.L., Hatfield, J.L., Spoth, K.K., Doorenbos, R.K. 2013. Crop/Wind-energy Experiment (CWEX): Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm. Bulletin of the American Meterological Society. 94:655-672. Interpretive Summary: Wind turbines provide a valuable source of alternative energy. In the upper midwest region there is an increasing trend in developing wind turbine farms that are located within the corn and soybean fields. In many cases the the number of turbines can be in the hundreds. The United States Department of Energy (DOE) has outlined a scenario describing how wind power can be a major contributor to meet future U.S. renewable energy needs (DOE 2008). While the co-location of wind farms with intensively managed agricultural production is possible, it leads to physical interactions between two otherwise separate economic systems. Crop selection and management determines surface drag and fluxes that influence hub-height wind speeds. By contrast, turbine-generated changes in mean wind, pressure, and turbulence may influence fluxes of heat, moisture, and CO2 that are of vital importance to biophysical crop processes. Little is known about the impact to crop yields from wind turbines that can alter near surface meteorological conditions. An array of meteorlogical instruments placed within the wind flow domain of a production corn field in central Iowa revealed disturbances in heat and momentum transfer that were directly related to wind turbine action. This result is the basis for further investigations that will include yield comparisons in fields under the influence of turbines with those not influenced by turbines. These results will benefit agriculture and energy sectors by providing real measurements.
Technical Abstract: Perturbations of mean and turbulent wind characteristics by large wind turbines modify fluxes between the vegetated surface and the lower boundary layer. While simulations have suggested that wind farms could significantly change surface fluxes of heat, momentum, moisture, and CO2 over hundreds of square kilometers, little observational evidence exists to test these predictions. Quantifying the influences of the “turbine layer” is necessary to quantify how surface fluxes are modified and to better forecast energy production by a wind farm. Changes in fluxes are particularly important in regions of intensely managed agriculture where crop growth and yield are highly dependent on subtle changes in moisture, heat, and CO2. Furthermore, speculations abound about the possible mesoscale consequences of boundary-layer changes that are produced by wind farms. To address the lack of observations to answer these questions, we developed the Crop/Wind-energy Experiment (CWEX) as a multi-agency, multi-university field program in central Iowa. Throughout the summer of 2010, surface fluxes were documented within a wind farm test site, and a two-week deployment of a vertically pointing LIDAR quantified wind profiles. In 2011, we expanded measurements at the site by deploying six flux stations and two wind-profiling LIDARs to document turbine wakes. The results provide valuable insights into the exchanges over a surface that has been modified by wind turbines and a base for a more comprehensive measurement program planned for the summer in 2013.