2012-06-28 / Editorial

Sounds from a Taylor Point turbine

VIEWPOINT
BY HARLEY LEE

When siting a wind turbine, the sound it creates is an important consideration. The contribution of wind energy to electricity in the United States has been rising rapidly for several years and there are now tens of thousands of wind turbines producing about 3 percent of the country’s electricity. While most of them have not caused sound problems, some have annoyed neighbors.

What could we expect from a wind turbine at Taylor Point? First let’s consider some sound basics.

Sound is measured in decibels. It’s not a linear scale, but logarithmic, so increments of sound level are greater as the numbers increase. As a result, sound levels are not additive. If a person talking at a distance of 3 feet is 60 dB, then two people talking might be 62 dB, not 120. Here’s are examples showing sound levels and examples from Maine’s Office of Energy Independence and Security:

• Apartment next to a freeway: 87 dB

• 3/4 mile from a runway of a major airport: 86

• Downtown with construction activity: 79

• Old urban residential area: 59

• Wooded residential: 52

• Agricultural cropland: 44

• Rural residential: 39

• Wilderness ambient: 35

Sound decreases rapidly with distance. Imagine starting at the Pell Bridge and walking south. By the time you reach the golf course, the sound level has dropped considerably.

On a still day, a wind turbine would make no sound as there is no wind. Wind turbines have their greatest sound impact with moderate winds – about 17 mph. Below that speed, the turbine puts out less sound. Above that speed, the background sound from the wind increases.

The Jamestown Police Department was helpful enough to take baseline measurements at three sites near Taylor Point: the Police Department driveway, one of the nearest residences is across the street; just outside the sewage treatment facility gate near the turbine site; and at the Wyndam Newport Overlook driveway. It took measurements at several times during the day and night. As one might expect, the day-time readings were often between 55 and 70 dB. When a truck drove by, readings sometimes went as high as 82 dB. Some readings in the wee hours of the morning went as low as 40 dB.

A modern turbine of the size Jamestown is considering will make about 55 dB of sound at the base of the turbine. Like the Portsmouth High School turbine, you can carry on a normal conversation at the base of the machine without raising your voice. The sound level drops off with distance. The windenergy feasibility report noted that Jamestown has a 60 dB sound limit. Since a turbine would be below that, the conclusion was that the turbine would meet local requirements.

Some precautions that Jamestown would be to:

• Use a turbine that is quieter in operation. The model of turbine that has caused problems in Falmouth, Mass., is a stall-regulated turbine that produces more sound than more modern turbines.

• Site the turbine appropriately. The town-owned land at Taylor Point is attractive as it is immediately next to the Pell Bridge, which has on the order of 30,000 vehicles per hour. The turbine will seldom be audible because of the background sound from traffic and the distance to residences.

• Seek a turbine with the capability to operate in low-noise mode. In this mode, a turbine will produce slightly less output and less sound. In the wee hours of the morning when traffic has subsided, if the wind is at a moderate speed from the northwest, it is possible that residents or visitors at the timeshare facility could hear the turbine. Having the ability to operate in a low-noise mode during these rare events could be helpful.

For those interested in hearing a turbine, you can visit the Portsmouth machine on a windy day and hear it for yourself. It is similar in size to what’s being proposed for Jamestown.

Jamestown has many sounds: traffic (especially from Route 138 and the bridges) foghorns (especially on the Pell Bridge), construction sounds, motorboats, seagulls, and many more. We’ll need to decide whether the swishing of a wind turbine should be one of them.

The author is president of Endless Energy Corporation, a consultant chosen by the Town Council in December to conduct studies necessary to determine the costs and potential profitability of a Jamestown wind turbine.

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