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Scituate Wind: More-than-predicted flicker

A recent study of shadow flicker from the Scituate Wind turbine, located off the Driftway, shows an effect to several residences in the neighborhood, with an impact higher than initially predicted to the nearest abutting property.

During the Jan. 7 Scituate Board of Selectmen meeting, former Department of Public Works (DPW) Director Al Bangert, working as a consultant for the town, introduced a presentation by representatives of EAPC Wind Energy Services of Vermont.

The EAPC analysis indicated an increase in shadow flicker at 151 Driftway as 69 hours per year compared with 51 hours per year as predicted by an earlier shadow flicker study.

The residential property of 151 Drifttway is located 640 feet from the base of the turbine.

“Shadow flicker occurs when rotating wind turbine blades cast a pulsating shadow on an observer or their immediate environment, such as a room or outdoor space,” said Chester Harvey of the EAPC. “Shadow flicker is similar to the experience of driving along a tree-lined road when low-angle sun is casting shadows through the trees and across the moving car, but at a lower frequency.”

Harvey explained daily sun paths based on latitude, local weather and wind data were used in desktop estimates of shadow flicker exposure. Field documentation of line-of-sight was assessed by car from public streets.

Bangert explained EAPC was hired to perform the study – funded by the Massachusetts Clean Energy Center – because the town wanted to “check the impact of shadow flicker after the construction of the turbine.”

“The original study was done before construction began as part of the Special Permit application,” he said.

The 390-foot Scituate Wind turbine went online in March of 2012.

Atlantic Design Engineers completed the initial shadow flicker study and concluded that the flicker impact at the nearest neighboring property, 151 Driftway, to be in the range of 51 hours per year.

“In recognition of this, the property owner was provided with mitigation in the form of mature evergreen trees along the property line and $20,000 in funds,” Bangert said.

The EAPC study notes that the difference in annual hours of shadow flicker is attributable to the use of a different set of assumptions for turbine uptime – 23 versus 20.3 hours per day, amount of wind from an unfavorable direction – 2,511 versus 1997 hours per year, and the size of the shadow receptor.

As to the study of minutes of flicker per day, the EAPC analysis indicates that the duration of flicker at 151 Driftway is 104 minutes versus the 91 minutes on the worst day.

Bangert said the difference could be attributed to the different size of receptor in the two studies.

“The EAPC study looked at the entire side of a house whereas the original study looked at impact upon a standard size window,” he said, adding that neither study could validate the three hours of flicker per day the property owner had stated in a complaint.

Shortly after the wind turbine went online, neighbors began to complain of nausea, sleeplessness, headaches, and other ailments they attributed to the turbine.

Several public forums were held before the Scituate Board of Health. Scituate Wind, LLC, the owner of the wind turbine, agreed to fund an acoustical study to determine if the turbine was operating in compliance with state regulations.

Preliminary test results from an acoustical study performed on the Scituate Wind turbine on the night of August 14 and early morning hours of August 15 came back within allowable state limits.

Bangert said the town would be exploring different options to provide additional buffering to 151 Driftway.

“One option being considered is constructing a shade wall on the property line between the sewer plant and the residence to reduce the incidence of shadow flicker,” he said.

There are currently no state mandates governing wind turbine shadow flicker.