September 29, 2008

A Fall Turbine Tour Will Blow You Away

By Paul g Wiegman

Fall brings many changes. One of them is the return of windy days.

Leaves move and flutter, ripples appear on water, and clouds sail across the sky.

Where does wind come from, or, a better question, how is it created?

Like nearly all energy on Earth, wind can be traced back to the sun. Wind is a form of solar energy.

It begins when the sun shines on a surface -- land or water. The surface is heated by the sun and the air above the surface also is heated.

Heated air is lighter than cool air and lighter air rises. Cooler air flows into the space left by the warm air and wind begins. This is termed convection -- warm air rising away from the Earth and cooler air falling.

On a global scale, air is warmed at the equator and rises. Cooler air from the poles flows in to replace the rising air. But wind isn't that simple.

While the air is going up or coming down, the Earth below is spinning. This bends the wind, creating global patterns that have been used for centuries, especially when humans depended on wind to move ships between continents.

In the north polar regions, there are prevailing easterly winds. Between 30 degrees north and 60 degrees north, the region in which we live, the winds generally are westerly, or moving from west to east. Below that belt, and to the equator, winds shift back to easterly, these are called the trade winds.

The picture is the same in the Southern Hemisphere. Between the belts of wind are calm areas. Around 30 degrees, between westerly and easterly winds, are the Horse Latitudes, a belt of calm air.

The name comes from a ritual from sailing ship days. Sailors were partially paid in advance for long voyages. The period for which they were paid was called dead horse time. The end of that period was time for celebration since now the sailors were earning new money. The crew paraded a dummy of a horse before throwing it overboard. Dead horse time ended about a month or two into the voyage, just about the time ships from Europe to North America were reaching the region of 30 degrees north, thus called the Horse Latitudes.

Along with large global wind patterns, there are locally generated winds. Sea breezes are a good example.

Land heats more rapidly than water, so during the middle of a hot day on a beach, hot land air is heated and rises. Air over water is cooler. It moves in to replace the rising land air and creates a sea breeze coming off the water; one reason we enjoy the breezy beach on a hot afternoon.

Here in Western Pennsylvania, one of the ways we see the wind is in the spinning of wind turbines.

Using wind to move ships, pump water and generate electricity has occurred for a long time. More recently, technology has advanced, and the kinetic energy of large masses of moving air can be changed to mechanical energy to generate electricity.

There are several arrays of wind turbines in the Allegheny Mountains, a.k.a. the Laurel Highlands, of Western Pennsylvania.

Watching these machines slowly turn, we are likely to think that wind pushes the blades and makes them turn. That is not the case. The blades are very much like airplane wings. Wind passing over the wing-shaped blades creates a low pressure on the bottom of the blade and they are "lifted" causing the blades to rotate. The blades of a typical turbine are attached to a central hub. The hub is attached to a generator and from that electricity is produced.

The best way to understand how a wind turbine works is to get close to watch one.

Suggested tour of the Laurel Highlands

Here is a suggested tour of the Laurel Highlands that provides a close-up look at one turbine array on Laurel Ridge near Mill Run, Fayette County. I'm suggesting this auto tour for another reason. We are about to experience the peak of fall color and this ride will provide a colorful look at fall.

One caveat: several roads on this route are dirt roads. They are well maintained, but be aware they're off the beaten path.

Beginning in Normalville, Fayette County, at the intersection of Route 381/711, take Route 381 South toward Mill Run and Ohiopyle. In just a few hundred feet, turn left onto Route 653 and go 4.6 miles to a turn to the right. Look for a sign for Cranberry Lake. After turning right, follow this road for 2.1 miles to a "Y" and bear left. Again, look for a Cranberry Lake sign.

This road leads to the summit of Laurel Ridge and the Mill Run Wind Farm in one-half mile. You can't miss the turbines, since they are right beside the road on either side. You can stop at a small pull-off for a closer look.

At this point, you are at just more than 2,600 feet above sea level. To the west is Chestnut Ridge, and to the east Negro Mountain and Mt. David, the highest point in Pennsylvania. The summit of Laurel Ridge is at an elevation where wind has few obstacles and thus the ridge tops have constant and strong winds, making it suitable for large wind turbines.

After visiting the Mill Run wind turbines, you can either turn around and go back to Route 653. Or, you can continue along the same road down the other side of Laurel Ridge, toward the east. Below is Cranberry Lake. The road passes alongside the northeast side of the lake. In about 4 miles is a "T" intersection. Turn left, and, in 5 miles, turn left again, and you will reach Route 281 at Ursina. Route 281 leads to Somerset and the Pennsylvania Turnpike.

On the ride to Somerset watch to the east for another wind farm. This larger array is on Negro Mountain and is the newest in Somerset County.

I hope you have a wonderful fall.

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