Assistant Professor Somnath Baidya Roy
Climate researchers have found a surprising and moderating effect on local temperatures generated by turbines on wind farms. The study found that the area immediately surrounding turbines was slightly cooler during the day and slightly warmer at night than the rest of the region. Led by University of Illinois professor of atmospheric sciences Somnath Baidya Roy, the research team has published its findings in the Proceedings of the National Academy of Sciences.
He first proposed a model describing the local climate impact of wind farms in a 2004 paper. Roy was interested in determining the processes that drive the daytime cooling and nocturnal warming effects.
But that and similar other studies were based on models because of the lack of available data. He identified an enhanced vertical mixing of warm and cool air in the atmosphere in the wake of the turbine rotors. The rotors generate turbulence as they turn. A rotor pulls down upper-level air toward the surface while it pushes up surface-level air, causing warmer and cooler air to mix. But does warming or cooling dominant?
In fact, no field data on temperature were publicly available for researchers to use until Roy met Neil Kelley at a 2009 conference. Kelley, a principal scientist at the National Wind Technology Center, part of the National Renewable Energy Laboratory, had collected temperature data at a wind farm in San Gorgonio, Calif., for several weeks in 1989. That data corroborated Roy’s modeling studies and provided the first observation-based evidence of wind farms’ effects on local temperature.
Roy found the dominant effect depends on location. “For example, in the Great Plains, winds are typically stronger at night, so the nocturnal effect may dominate. In a region where daytime winds are stronger – for example a sea breeze – then the cooling effect will dominate. It’s location specific.”
Wind farms, especially in the Midwest, are on farmland. Roy says nocturnal warming could offer farmland some measure of frost protection and may even slightly extend the growing season.
Understanding the temperature effects and processes that cause them also lets researchers develop strategies to mitigate wind farms’ impact on local climate. The group identified two possible solutions: Low-turbulence rotors and building wind farms in more turbulent locals. Less turbulence rotors would lead to less vertical mixing and therefore less climate impact.
In the second strategy, turbulence from rotors has much less consequence in an already turbulent atmosphere. Global data can identify regions where temperature effects of large wind farms are likely to be low because of natural mixing in the atmosphere, providing ideal sites. “These regions include the Midwest and the Great Plains as well as large parts of Europe and China,” says Roy. “This was a coarse-scale study, but it would be easy to do a local-scale study to compare possible locations.”
University of Illinois
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