Large groups of power-generating windmills could have a small but detectable influence on a region’s climate, new analyses suggest.
Windmills once were quaint several-story-high mechanisms that pumped water or ground grain. They’ve since evolved into sky-scraping behemoths that can each generate electrical power for more than 100 homes.
Some modern turbines are 72 meters tall and have rotor blades that are about 25 m long, says S. Baidya Roy of Duke University in Durham, N.C. Future windmills may reach higher than 100 m, and their rotor blades may measure 50 m long, he notes.
All such turbines disrupt natural airflow to extract energy from wind. To investigate potential effects of a wind farm that includes thousands of windmills, Roy and his colleagues used a detailed climate model based on wind speeds, temperatures, and ground-level evaporation in north-central Oklahoma during a 2-week period in July 1995. In their scenario, the researchers considered a 100-by-100 array of windmills spaced 1 kilometer apart.
The simulation suggests that during the day, while sun-induced convection handily mixes the lower layers of the atmosphere, such a wind farm wouldn’t have important climatic effects.
In predawn hours, however, when the atmosphere typically is less turbulent, a large windmill array could influence the local climate. For example, at 3 a.m., the average wind speed at ground level was 3.5 meters per second (m/s) in the absence of windmills. Adding the wind farm would increase the average wind speed to 5 m/s. Also, the 10,000 windmills would increase the temperature across the area by about 2°C for several hours.
Averaged over an entire day, the wind speed at ground level would go up about 0.6 m/s and the temperature would jump 0.7°C.
Turbulence caused by the rotating blades would shunt some of the high-speed winds typically found 100 m off the ground down to Earth’s surface, says Roy. Those surface winds would boost evaporation of soil moisture by as much as 0.3 millimeter per day.
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The researchers describe their simulation in the Oct. 16 Journal of Geophysical Research (Atmospheres).
The findings may stimulate scientists to validate the analysis with real-world tests, says Neil Kelley, a meteorologist at the National Renewable Energy Laboratory in Golden, Colo. In general, says Kelley, the simulation agrees with atmospheric data he gathered at a wind farm in California.