Wind turbines generate electricity without releasing carbon dioxide, a greenhouse gas. Wind turbines may also have an additional benefit when installed on crop land. The base of the wind turbine takes up a relatively small amount of area allowing crops to continue to be grown in the field after construction of the wind turbine. The turbine blades affect the airflow across the top of the fields by slowing the wind and creating vortices off the tips of the blades. Crops consume carbon dioxide during photosynthesis and grow faster if a higher concentration of carbon dioxide is available. Research is being conducted to determine if wind turbines can increase the carbon dioxide concentration of the air that the plant uptakes by mixing the boundary layer with air that has an atmospheric concentration of carbon dioxide.
If the turbine is shown to mix the air sufficiently at night, the evaporation of water may increase. On the nights when dew condenses onto the crops, fungi can more easily grow, and an increased evaporation could lower the risk of fungal growth. The turbines slow the wind speed, and if significant, the air temperature during the day will be cooler and the temperature at night will be warmer. The crops will grow faster if there is less frost risk or less stressed on very hot days. There are several variables that are difficult to quantity, but if positive results are found for the growth of crops, land owners may be more willing to have wind farms installed.
The wake behind the turbine is monitored using light emitting radar, lidar. Wind turbines being installed currently are much higher than the crops below them, but initial studies have found that the wake behind the turbines reach down two to three times the tower height, reaching the ground in some cases. A study in 2010 conducted in Southern California found that night time temperatures were warmer downwind of wind turbines.
This research may not have a widespread use. Surveys of the United States show that wind resources are concentrated in the High Plains, just East of the Rocky Mountains. Significant portions of this area will not grow crops without irrigation. This region was once referred to as the Great American Desert but today is covered with center pivot irrigation. With the water use higher than the rate of precipitation, this is not a sustainable area to grow food. Generating electricity may be a much better use of this land when the area is reclaimed by the desert.
Understanding in detail how the wind is affected by a wind farm is useful in areas other than crop land. The research can affect turbine design or the pattern in which the turbines are laid out to increase efficiency. The overlap between sustainable crop land and good wind resources may be developed more quickly if the results from this study show that wind turbines increase the growth rate of crops.