US researchers have discovered that wind farms produce a distinct effect on the temperatures of the land on which they are sited.
The discovery came as the result of an analysis on temperature data collected at a wind farm in San Gorgonio, California, over a period of seven weeks by Neil Kelley, a principal scientist at the National Wind Technology Center, part of the National Renewable Energy Laboratory.
Analysis of Kelley’s data corroborated modelling studies carried out by University of Illinois professor of atmospheric sciences Somnath Baidya Roy, providing the first evidence of the effect of wind farms on local temperature.
The study found that the area immediately surrounding the turbines was slightly cooler during the day and slightly warmer at night than the rest of the region.
Interested in determining the processes that drive the daytime cooling and nocturnal warming effects, Roy identified an enhanced vertical mixing of warm and cool air in the atmosphere in the wake of the turbine rotors. As the rotors turn, they generate turbulence, like the wake of a speedboat motor. Upper-level air is pulled down toward the surface while surface-level air is pushed up, causing warmer and cooler air to mix.
’Whether warming or cooling becomes the predominant effect at any given wind-farm site depends on its location,’ Roy said.
Many wind farms, especially in the Midwestern United States, are located on farmland. According to Roy, the nocturnal warming effect could offer such farmland some measure of frost protection and may even slightly extend the growing season.
Understanding the temperature effects and the processes that cause them also allows researchers to develop strategies to mitigate the impact of wind farms on local climate. The group identified two possible solutions. First, engineers could develop lower-turbulence rotors. Less turbulence would not only lead to less vertical mixing and therefore less climate impact, but also would be more efficient for energy generation. However, research and development for such a device could be a costly, labour-intensive process.
The second mediation strategy is to locate turbines where the effect would be lower because of natural turbulent mixing of air in the atmosphere, where turbulence from the rotors has much less consequence. The researchers used global data to identify regions in the Midwest and the Great Plains as well as large parts of Europe and China that would provide such ideal sites.
Next, Roy’s group will generate models looking at both temperature and moisture transport using data from and simulations of commercial rotors and turbines. They also plan to study the extent of the thermodynamic effects, both in terms of local magnitude and of how far downwind the effects spread.