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Warm air down and cold air up: wind farms may affect weather

Esther Han

April 30, 2012 – 7:37am

As Australia turns towards renewable sources such as wind power in a bid to reduce carbon emissions, a study from the United States has found wind farms themselves may be affecting local weather and land surface temperatures.

An analysis of land surface temperatures of regions around large wind farms in Texas from 2003 to last year shows wind turbines can produce a night-time warming trend of up to 0.72 degrees per decade, researchers from the University of Albany in New York have found.

The researchers explained in the journal Nature Cli-mate Change that wind turbines acted like fans, pulling warmer “near surface air” from higher altitudes at night.

Liming Zhou, lead author of the study, said: “Typically at night there’s a stable atmosphere with a warm layer overlying a cool layer.

“Enhanced vertical mixing brings warm air down and cold air up, leading to a warming near the surface at night.”

NASA satellite data revealed a persistent upward trend of land surface temperatures, consistent with the growth in number of local wind turbines over the same time period. Mr Zhou concedes the warming effect could reach a stable level if no wind farms are built.

Wind power is Australia’s fastest-growing renewable energy source. Late last year, there were 1188 wind turbines in 57 wind farms in Australia.

Mr Zhou described the research as “small and local”, adding therefore the results should not be applied on a global scale or over longer time frames.

“We are now expanding this approach to other wind farms and building models to understand the physical processes and mechanisms driving the interaction of wind turbines and the atmosphere boundary layer near the surface,” he said.

He acknowledges wind power is part of the solution to climate change, pollution and energy security problems.

“Generating wind power creates no emissions, uses no water and is likely green,” he said.

“The research is critical for developing efficient adapting and management strategies to ensure long-term sustainability of wind power.” Professor Steven Sherwood, the co-director of the Climate Change Research Centre at the University of NSW, said the study was solid and made sense.

“Since at night the ground becomes much cooler than the air just a few hundred metres above the surface, and the wind farms generate gentle turbulence near the ground that causes these to mix together, thus the ground doesn’t get quite as cool,” he said.

“This same strategy is commonly used by fruit growers who fly helicopters over the orchards rather than windmills to combat early morning frosts.”

The University of Albany and the National Science Foundation in the US funded the Zhou study.

Earlier this year the NSW government announced a six-month noise audit at three wind farms, despite protests from the industry.

NSW Planning Minister Brad Hazzard announced the audit of Capital, Cullerin Range and Woodlawn wind farms, all in southern NSW, because of complaints from residents. The audit will also involve a questionnaire, meetings and a public information line, and will also consider other impacts such as “visual amenity, flora and fauna impacts, blade flicker, community contributions and electromagnetic interference”.

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