WHILE harnessing wind energy could satisfy growing demand for electricity and reduce emissions of greenhouse gases, turbulence from wind turbines could affect the growth of surrounding crops, US researchers said. Led by atmospheric sciences professor at University of Illinois, Somnath Baidya Roy, the researchers suggest careful placement of windfarms.
Roy had first described the local climate impact of wind farms in 2004. The study was based on models because little data on temperatures at wind farms was available in the public domain. In 2009, Roy met Neil Kelley, meteorologist at the National Renewable Energy Laboratory in Colorado, who had collected temperature data at a wind farm in the foothills of the San Jacinto mountains in California for seven weeks in 1989.
Roy and his team analysed Kelley’s data and found the area surrounding turbines was up to 3.5oC cooler during the day and up to 0.61oC warmer at night than the rest of the region. Spinning turbine rotors create turbulence in their wake, which mixes air up and down. During the daytime, the surface air is warmer than air above.
Turbulent mixing brings cold air down and takes warm air up, leading to a cooler surface. Likewise, turbulent mixing at night results in a warmer surface. This creates a stronger mixing of heat and moisture, which causes the land surface to become warmer and drier at night, the researcher noted in the October issue of Proceedings of the National Academy of Sciences. Kelley agrees with the findings. “Although the wind farms had minimum spacing and the turbines were smaller we found the turbines tend to pull down heat from upper air, particularly at night,” he said.
This change in hydrometeorological conditions can affect the growth of crops within the wind farm because warm temperature at night robs plants of moisture, Roy said. Since more wind turbines are coming up on farmland, helping farmers supplement their income with rent from energy companies, Roy proposed strategies to reduce the impact of wind turbines on local weather and thus the crops.
One, identify regions where both wind energy and its frictional dissipation are high. Some of the wind’s kinetic energy is lost as friction as it passes over and around obstructions such as trees, high-rise buildings and mountains. Installing wind turbines in areas where frictional dissipation is high would mean minimal intrusion on the wind’s natural kinetic energy cycle.
Although the tops of mountain ranges and plateaus are suitable regions, constructing wind farms there would be impractical and economically unfeasible. Researchers must, therefore, search for suitable regions. Roy is already mapping the wind’s frictional dissipation around the world. It shows large parts of North and central America, southern tip of South America, northern Europe, Russia, northern China, the Rift Valley and southern parts of Africa and southern Australia are ideal for low-impact wind farms.
Engineers can also design low-turbulence rotors and plan spacing between turbines to reduce their impact, Roy suggested.
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