Will serrated edges slice turbine noise at the Hoosac? 

As the installation of new turbine blade edges began in Monroe last week (October 25, 2014), residents of Monroe and Florida can only hope that the saw-toothed edges will make a dent in the turbine noise plaguing them. An industrial-sized crow’s nest allowed technicians to apply GE’s experimental fix for Iberdrola’s out-of-compliance turbines. The blade being worked on in the photo at left is in the top middle of the frame. Below is a close-up of the “Serrated TE” GE uses to reduce blade noise. [photographs available at source]

According to a letter and report from Iberdrola to the MassDEP, the violations at the Hoosac ranged from 10.2 dBA above background in January 2014 to 17 dBA in February. The Serrated TE reduces broadband noise by 2 to 4 dBA according to Totaro & Associates of Houston Texas.

This is the first time an attempt has been made to mitigate turbine noise in Massachusetts while keeping the turbines running. Previous orders have required shut downs for certain hours of operation. The serrated trailing edge retrofit allows the wind turbine operator to continue to produce electricity while testing an unproven noise reduction technology.

According to Jim Cummings in “Addressing Wind Farm Noise Concerns” (Acoustic Ecology Institute, Dec 2012):

Aerodynamic noise from the trailing edge of turbine blades is the primary noise source of most modern turbines. This is generally a broadband noise, though most notable at frequencies of 700Hz to 2kHz. A range of design modifications are being developed by most turbine manufacturers, including shape of the airfoil, tip modifications, vortex generators along the fin’s crest, and porous or serrated trailing edges. Serrated edges appear to be the most widely studied, with overall noise reductions of 3-8dB being reported (Barone, 2011). However, many studies have found that these reductions are frequency-dependent, with reductions in low-frequency noise and increases at higher frequencies (over 2kHz). Serrations may be less effective at low or moderate wind speeds; in some situations, this can be when neighbors find turbine noise most audible.

Residents have filed multiple complaints to the MassDEP regarding the noise experienced West of Bakke Mountain, in Florida and Clarksburg, and on Moores and Tilda Hill roads in Florida and Monroe. However Iberdrola is only installing serrated edges on half the turbines on its industrial wind complex, meaning that those affected by Bakke Mountain turbines will not benefit.

Although noise and the consequent lack of sleep are the primary concerns for people living near the turbines, there is growing evidence that turbines also affect people through low-frequency emissions. Photographer Larry Lorusso, who lives one mile west of the turbines in Clarksburg, states that he is awoken in the night by the turbines. Michael Fairneny and his wife report adverse health effects at their home on Moores Road, one-half mile from the turbines. The health effects were so severe for Tim Danyliw and Nancy Shea that they abandoned the home they were renovating on Tilda Hill Road.

Serrated edge applications were made to the turbines operating in Vinalhaven, Maine as a beta test. No other turbines with noise violations in Massachusetts have used this technology.