Wind Farms May Threaten Crop Production

Published February 1, 2005

A new simulation has found serious and previously unrecognized environmental threats from massive wind farms in the American Great Plains.

A recent study by scientists from Princeton and Duke Universities, “Can large wind farms affect local meteorology?” published in the October 2004 issue of Journal of Geophysical Research, indicates massive wind farms would significantly increase local surface drying and soil heating, which in turn would affect agricultural or range use on or near the wind farms.

Accurate Simulation

The modeling experiment used current wind turbine and rotor technology to assess local climate impacts from a simulated wind farm with 10,000 turbines arranged in a simple, square array of 100 by 100 turbines, each spaced one kilometer apart.

Each turbine was fixed in the simulation at 100 meters above ground, with the full sweep of the blades at 100 meters in diameter. That artificial design is close to that of some modern wind turbines.

For example, the world’s largest wind turbine, currently being installed at Brunsbttell, Germany, northwest of Hamburg, is 120 meters tall with a rotor spanning 126 meters. The 80-megawatt Top of Iowa Wind Farm at Kensett has 89 turbines, each standing 72 meters tall.

Although the number of turbines in the Princeton-Duke study is much larger than those wind farms, it is nearer the scale of wind farms that would be needed to provide the significant amount of energy promoters of wind power envision.

After designing the hypothetical wind farm, the authors of the study then simulated the changes in summer meteorological conditions imposed by the wind farm during wet or dry weather periods.

Atmospheric Disturbances

One finding was that 10,000 wind turbines operating in a location with conditions similar to those of north-central Oklahoma would reduce local wind speeds at heights of approximately 100 to 400 meters above ground, which would significantly reduce the amount of power the turbines could produce.

For example, the virtual wind farm would slow the wind speed at 3 a.m. at a height of 100 meters above the ground by 3 meters per second. That would represent a roughly 30 percent reduction from the baseline wind speed if there were no wind farm. That, in turn, would greatly reduce the power–already intermittent because of the variability of wind–as power extracted by turbines depends on the cube of the wind speed.

The Princeton-Duke study also addressed for the first time other effects of large-size wind farms on local weather.

The authors note concern about wind farms is not centered on the small amount of energy extracted from the atmosphere. Wind farms on average extract only about 1 watt of energy per square meter from the atmosphere. That amount is small compared to the tens to hundreds of watts per square meter of kinetic and potential energy available in the atmosphere.

The Princeton-Duke authors are concerned, however, with the rapid whirling of the blades, which will strongly churn the local air and generate significant turbulence. That turbulence changes the distribution of moisture and heat in a volume of air much greater than the actual size of the turbine: The turbulence made by the turbines extends to heights of 1 kilometer above ground.

Artificial Warming

According to the model results, turbulence from 10,000 turbines would warm the air near the ground by 2º C for several hours each day during the summer and about 0.7º C averaged over a full day. The turbulence also would promote significant evaporation of soil moisture, drying the soil at a rate of 0.3 mm/day (the amount of water, measured like rainfall, that the turbulence will cause to evaporate each day).

During the statewide drought conditions of August 2000 in Oklahoma, the estimated moisture drawn from the soil around a large wind farm would have been twice as great as the available rainfall, thus exacerbating the drought.

The Princeton-Duke study expands the scope of proper environmental assessments necessary for wind farm siting and adds to problems already associated with wind farms, such as noise and visual pollution, lowered residential property values, and destruction of birds and their habitats.

The pro-nuclear energy and pro-science-and-technology British scientist Professor James Lovelock, originator of the concept of the Earth as a complex organism called Gaia, recently commented on the idea of carpeting the Earth with wind farms to meet energy needs:

“We need no more sustainable development, what we need is a well-planned sustainable retreat. Inevitably, we will make mistakes, especially when we are still so amazingly ignorant about the Earth system. Renewable energy sounds benign and is just what the Earth needs; but imagine that the extraction of power by wind turbines became a major energy source–would it be entirely free of larger consequences?

“I don’t lose sleep over the thought that eddies shed by a single butterfly’s wing might be the progenitor of a tornado that blew down my house,” Lovelock continued, “but I do wonder whether a million giant wind turbines adversely affect the vorticity of the atmosphere.”

Dr. Willie Soon is a physicist at the Solar, Stellar, and Planetary Sciences Division of the Harvard-Smithsonian Center for Astrophysics and an astronomer at the Mount Wilson Observatory. He is also science director for Tech Central Station. Dr. Sallie Baliunas served as deputy director of Mount Wilson Observatory and as senior scientist at the George C. Marshall Institute in Washington, D.C., and chairs the institute’s Science Advisory Board. This article was first published by Tech Central Station (, and is reprinted here with permission.