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Wind farms, yes, but not on ridges  

I am an aerospace engineer. I lived in the high desert north of Los Angeles from 1983 to 1994. I first worked at the Naval Weapons Center at China Lake, Calif., and later moved nearer to the town of Mojave. Among the many interesting sights in the high desert is that of the thousands of wind turbines in Tehachapi Pass (between Mojave and Bakersfield).

Partly because of this experience, I am a strong advocate of wind power. But the letter from Richard White (“Windmills won’t destroy mountaintops,” Nov. 30) advocating 40,000 wind turbines along the Appalachian Mountains is so absurd that it has caused me to write in response to the nonsense proposed by local fans (pun intended) of wind power.

As an engineer, I am going to provide a slightly technical introduction to the horizontal axis wind turbine (rather than rant and rave with only emotional energy, another pun intended):

n The average wind velocity is critical to the efficiency of a windmill and one must consider the year-round, 24-hour average velocity when selecting a site. Consistently moderate winds (15-30 miles per hour) are the best choice. Most wind turbines in California are located in mountain passes where air funnels through at a significantly increased velocity.

n In general, because of turbulence, wind turbines are not positioned on ridge lines, certainly none in California in the Sierras during that time frame.

n The blade on a wind turbine is really a wing. The primary factor governing the efficiency of any wing is the aspect ratio (basically the length divided by the average width of the blade) and this causes designers to make the wing (or blade) as long as is structurally feasible; current technology makes the “sweet spot” for wind turbine blade length in the range of 75 to 100 feet per blade.

With a total diameter of 200 feet, turning at 17.5 revolutions per minute, the tip velocity is 125 miles per hour.

n The airflow across the blade is most efficient at the tip, but to make the blade as efficient as possible over its entire length, the blade must become wider and thicker as the distance to the hub is reduced. These factors result in a mass of several thousand pounds per blade.

Because I have actually visited the site of a wind turbine in full flight, I am sure most of the local advocates of wind power have had no such experience.

To put this in terms to which the average reader can relate, I suggest they stand 20 feet from Interstate 81 with trucks passing by at 125 mph once per second. This would be sufficient kinetic energy to drop-kick a Prius from downtown to the airport.

It seems obvious that most of the local proponents of wind turbines have no idea:

n Of the site requirements to make an effective and profitable wind farm.

n That the more than 13,000 wind turbines in California (population, 37 million) can still produce only about 1.5 percent of its electric power needs .

n That White’s claim that “only” 40,000 wind turbines can produce all of the power for the Atlantic states is beyond absurd. The 40,000 wind turbines he mentions could produce less than 2 percent of the power required.

n Of the physical scale of the systems they are talking about.

n That offering tax incentives to developers obscures the true cost/benefit ratio.

n That such tax incentives are an obscene abuse of the taxpayer.

Wind turbines have a place in the energy plan for the United States, but putting them on Appalachian ridgelines in the Atlantic states is the wrong technology in the wrong place.

By Manley C. Butler Jr.

Butler is president of Butler Parachute Systems Group Inc. in Roanoke.

The Roanoke Times

10 December 2007

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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