The Carlisle Mosquito Online

Friday, March 20, 2009

Wind turbine bylaw hearing draws crowd

A near-capacity audience attended the March 9 public hearing on the proposed new bylaw on Wind Energy Conversion Systems held by the Planning Board and the Alternate Energy Generation Committee. The proposal would establish standards for locating and using wind turbines in any zoning district by special permit issued by the Zoning Board of Appeals (ZBA). The meeting took on the quality of a collaborative working session with the committee embracing concerns and comments from all participants.

When contacted later, committee member and Town Coordinator Elizabeth Barnett said that after the public hearing was closed, the committee worked late into the night to incorporate constructive changes into the proposed bylaw. The draft is available at Town Hall for review and will be posted on the town website when the Town Meeting Warrant is finalized.

Following are summaries of the proposed changes as incorporated in the present draft, the rationale as presented at the hearing, and some background information.

Section Setback: The wind turbine tower shall be set back at least one tower height plus one rotor radius from any property line, except that setback may be reduced by the Board of Appeals with the explicit agreement of the abutters, if the Board of Appeals finds there is no risk to the public safety or welfare. In making this determination the ZBA may consider the safety record for the type of wind turbine proposed and the consequences of tower failure for the proposed type of tower.

Several residents said that having a fixed minimum setback could be overly restrictive since, given the peculiar shape of some lots, there could be locations closer to a lot boundary that would be less intrusive to abutters. This latitude will be given to the ZBA but only with the explicit agreement of abutters. Noise: The applicant will provide noise data that shows the noise level at any property line will not exceed 5dBA and 5dBC* above the ambient level at ground level at the property line when the unit is operating in average wind speed conditions for the site.

Ray Modeen cited and said that low frequency noise should also be considered for a wind turbine installation. Committee member Keith Therrien agreed: “This makes a lot of sense; we should revisit noise.” The committee incorporated this change.

*[The letters A and C after the abbreviation dB described a frequency response function that filters sounds that are picked up by the microphone in a sound level meter. Frequency response means that some frequencies are given more importance than others.

A-weighting filters out low frequencies whereas C-weighting does no filtering at all. A-weighting is typically used to measure hearing risk for compliance with OSHA (Occupational Safety and Health Administration) regulations in industrial facilities.

However, some studies related to wind farms as cited on the web site suggest that low frequencies can have psychological, physical and cognitive consequences. One 2008 reference by Kemperman Associates, Inc. that is cited, (Why Noise Criteria Are Necessary for Proper Siting of Wind Turbines) states, “It is the low frequency aspect of wind turbine emissions that creates the ‘rumble problem’ indoors, plus building vibration, and this can be addressed solely with C-weighted criteria.”

Sound “emissions” refer to sounds as heard at the receiving location. “Emissions” refer to the sound from the perspective of the sound source.] Tower Type: Lattice and monopole towers may be allowed by the special permit granting authority. Guyed towers are prohibited. Towers must be hinged for maintenance and lowering in high wind conditions.

Wind turbine affect on birds

Planning Board Chair Greg Peterson questioned whether wind turbines and specifically the use of lattice towers could contribute to bird kills, as has been experienced at Altamont Pass, California.

The website, dated 2003, has an extensive bibliography on the topic of bird kills related to commercial wind farms. The author has the following assessment of the raptor kills that was cited by Peterson: “Since the mid-1980’s, a number of research organizations, universities, and consultants have conducted studies on avian mortality due to wind turbines. In the U.S., these studies were prompted because of the relatively high number of raptors that were found dead at the Altamont Pass Wind Farms near San Francisco”

The website also states, “After dozens of studies spanning nearly two decades, we now know that the Altamont Pass situation is unusual in the U.S. The high raptor mortality there was the result of a convergence of factors, some of which were due to the bad siting in the local ecosystem while others were due to the wind turbine and tower technology used at the time. In fact, a very different situation exists not far away at the San Gorgonio Pass Wind Farms near Palm Springs. A 1986 study found that 69 million birds flew though the San Gorgonio Pass during the Spring and Fall migrations. During both migrating seasons, only 38 dead birds were found during that typical year, representing only 0.00006% of the migrating population.”]

Other than discussing the concern, no changes were made in this section of the proposed bylaw. Output: Any wind turbine generating over 50 kilowatts is not covered by this bylaw and is not permitted with the exception of municipal applications.

Alan Lehotsky said, “I would like to see the bylaw permit greater than 50 kW for municipal and multiple users.” Amy Izatt cited the American Wind Energy Association ( as a good resource. Bruce Metcalf asked, “Why 50 kW? A 200 amp home service is 20 kW. It is conceivable to have two neighbors who would have wind turbines.”

Shadowing / Flicker: Wind turbines shall be designed and sited in a manner that does not result in significant shadowing or flicker impacts on surrounding neighborhoods. Data must be provided to support this.

Flicker refers to the moving shadow due to the rotating turbine blades. A You Tube video can be accessed at It shows an extreme example of flicker due to a wind farm. ∆

© 2009 The Carlisle Mosquito