Published: February 05, 2009 07:59 pm      

Must birds, bats be hurt by wind farms?

As an example, consider the Dan’s Mountain Wind Farm Project where likely 25 large wind turbines will be erected to convert wind energy into electrical energy for the electrical grid.

Each of the turbines will have three blades, each about 48 meters long and two meters wide. The area of the blades as they rotate will be (Pi*radius2 ) 7240 square meters or 1.8 acres. So the entire wind area used by these wind turbines will be about 45 acres.

Dan’s Mountain Wind Force, LLC has leased about 2,000 acres, covering a length of four miles or 6,440 m of which the towers will sit on 150 acres that will be cleared.

The towers are positioned at least 10 rotor diameters apart or 960 meters apart, the width of 10 football fields. (If they are closer, they will interfere with each other’s wind flow and lower their efficiency.) So if the towers are spaced every 960 meters, the free space (not in the rotor swing) is about 90 percent for a line of wind turbines.

Now due to Bernoulli’s Principle, as the wind increases the pressure drops. Will these wind turbines be change the wind velocity, resulting in lower pressure and then sucking birds and bats into their sweeping area?

You have experienced Bernoulli’s Principle when on a gusty, rainy day, your umbrella will suddenly turn itself inside out. (Faster air on top of the umbrella will have lower pressure than the air just below the umbrella; this creates a pressure difference to push up on umbrella and cause the wire supports to flip up instead of down.)

By noticing the wind blades in the nearby Pocahontas, Pa., wind farm, their 30-meter long blades typically spin all the way around in two seconds on a windy day. (There are twenty 1.35 megawatts towers in this wind farm that have operating for several years. You can see them easily by taking the Finzel Exit on I-68 and traveling north into Pennsylvania.)

Their tip blade velocity will be 94 m/s or 339 km/sec or 211 mi/hr. So the speed of the blade (which depends on distance from the axis) can be as fast as a dozen times a strong wind. (If the wind is too strong, the wind turbines are shut down.)

So at the tip of the wind turbine blades, the speed is comparable to the air speed of a propeller driven plane; this would lower the air pressure around the turning rotor blades. (In the recent New York airplane incident where the pilot landed his plane in the Hudson River, some large birds were sucked into both engines at over 3000 feet altitude, causing the engines to shut down.)

This Bernoulli drop in the air pressure will weaken with distance from the turning rotors. (So these turbines will not be acting like huge vacuum cleaners, drawing objects and debris into them and likely scarring the fiber glass blades, and shortening their service life.)

I have suggested in several past columns that ultrasonic speakers be placed on the towers beneath the spinning rotors. These ultrasonic speakers, powered by each turbine’s own electricity, would send out alarm signals to both bats and birds, driving them away from the towers when the rotor blades were turning.

Ultrasonic means a frequency beyond the human hearing range, but disturbing to winged creatures near the towers. Some readers may have small external devices on their cars that catch the air and shriek at frequencies that drive away deer.

Perhaps you have used a dog whistle. Why can’t even more powerful noise speakers be used for the towers to protect birds and bats? It has been suggested that such devices be installed on passenger planes to avoid collisions with flocks of birds.

Tomorrow evening we have a full moon, appearing near the bright star Regulus of Leo. (Regulus was one of the four Royal Stars of Persia, four bright stars that appear along the moon’s path; the other three stars are Aldebaran in Taurus, Spica in Virgo and Antares in the Scorpion).

On the next two evenings, the moon will appear near the planet Saturn; the moon will be above and to the right of Saturn on Tuesday evening and below and to the left of Saturn on Wednesday evening.

This Friday is Feb. 13, which will repeat in March and November of this year. Actually, there are slightly more Friday the 13ths, than Saturday, Sunday, and Thursday the 13ths. Most years have at least one or two Friday the 13ths , with about 15 percent of years having three.

In the southeastern dawn (about 6:20 a.m.), the planet Mercury can be seen close to the horizon. About half hour later, the bright planet Jupiter rises. In February’s last week, Jupiter and Mercury appear close.

Now showing at the Frostburg State Planetarium is “Tropical Skies”, exploring unusual sky sights seen near the equator. We also include an informal tour of our current evening skies. Our programs are at 4 p.m. and 7 p.m. on Sundays. All of our presentations are free and live, allowing questions during the program. I regularly stop talking and let questions be asked.

The Planetarium is in Tawes 302. Tawes is a medium sized building with its name on the front, across the street from the larger 4 storey Compton Science Center. Tawes is in back (northwest) of the Performing Arts Center. There is convenient free nearby parking, for on Sundays there are no regular classes at Frostburg State.

For any comments or questions from readers, contact Bob Doyle either by phone (301)687-7799 or email ( rdoyle@frostburg.edu ).