• Updated April 29, 2012, 7:33 p.m. ET   Wall Street Journal

Large Wind Farms Increase Temperatures Near Ground

By ROBERT LEE HOTZ

Large wind farms slightly increase temperatures near the ground as the turbines' rotor blades pull down warm air, according to researchers who analyzed nine years of satellite readings around four of the world's biggest wind farms.
The study showed for the first time that wind farms of a certain scale, while producing clean, renewable energy, do have some long-term effect on the immediate environment.

Using sensors aboard a NASA satellite, researchers at the University at Albany-State University of New York, and the University of Illinois systematically tracked a cluster of wind farms in central Texas as the installations grew from a few dozen turbines in 2003 to more than 2,350 by 2011.

On average, the nighttime air around the wind farms became about 0.72 degree Celsius warmer over that time, compared with the surrounding area, the scientists reported Sunday in the peer-reviewed journal Nature Climate Change.

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Cows graze near turbines at a wind farm in South Texas.

"The warming trend corresponds very well with the growth of the wind turbines," said wind-energy expert Somnath Baidya Roy at the University of Illinois, who was part of the research group. "The warming is going to level off when you stop adding more turbines."

Despite long-standing interest in the environmental impacts of such large-scale alternative-energy installations, this is the first time anyone has measured how wind turbines can alter local temperatures over the long term, the scientists said. So far, the scientists don't know if these higher temperatures affect local rainfall or other weather patterns.
"We don't know whether there is a change in weather due to the temperature change," said atmospheric scientist Liming Zhou at the University at Albany, who led the study, which was funded by the National Science Foundation. "The temperature change is small."

As wind farms become popular and much more widespread, however, they "might have noticeable impacts on local-to-regional weather and climate," Mr. Zhou said. But more research is needed, he said.


The researchers didn't identify the companies operating the wind farms in the region where they monitored temperature changes. To track the growing numbers of wind turbines in the area, the scientists used records kept by the Federal Aviation Administration of construction projects that might interfere with air safety.

Texas has more wind-turbine capacity than any other U.S. state, with many large commercial wind farms. Typically, these commercial wind turbines each sit atop a tower about 250 feet tall, capturing the wind with rotor blades that are about 100 feet long, Mr. Roy said.

Normally, the nighttime air is a layer cake of cool and warm air, caused as hot air rises and cold air sinks, with the coolest air closest to the ground. As the giant rotor blades churn the air, they draw the warmer nighttime air down to the surface.

"If you have a wind turbine spinning, there is a lot of turbulence in the wake just like a boat in the water," said Mr. Roy. "The turbine pulls warm air from aloft and pulls it down and takes cooler air underneath and pushes it up. That creates a warming effect near the surface."

Although the researchers detected some daytime warming because of the wind farms, the temperature changes were highest in the predawn hours, when the air normally is still and not so turbulent, the researchers said.

Write to Robert Lee Hotz at sciencejournal@wsj.com