More on Noise Report at Monroe Turbine
In her Greenfield Recorder news article, Study: Monroe turbines too noisy (8/1/14), reporter Diane Broncaccio reveals more details on actions taken to address Hoosac Wind’s noise.
Since the letter was written, Iberdrola Renewables has invited 60 neighbors to an information session, to hear landowners’ concerns, give them copies of the sound test results and discuss the planned modifications.
Those modifications include
∎ Install trailing edge serrations (saw-like edges) on the blades to reduce the overall turbine sound.
∎ Develop an operational protocol to address potential turbine noise for when the blades are coated with ice.
∎ Hire an independent engineering service to “study the tonality in more detail.” According to Western Mass. DEP spokeswoman Catherine Skiba, a tonality study is a detailed analysis of where on the turbine the sounds are coming from.
Skiba said the DEP has received 58 complaints since December 2012. [Note: with no Boards of Health in either Monroe or Florida, residents must complain directly to the MADEP].
For more information on the noise report and DEP response, see Hoosac Wind Fails Noise Test.
This is the first case in Massachusetts that Wind Wise is aware of where a “pure tone” has been noted in noise testing. Trailing edge serrations have been tried in Vinalhaven ME with mixed results.
Serrated edges appear to be the most widely studied, with overall noise reductions of 3-8dB being reported (Barrone, 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.
During its first summer in operation, the three Fox Islands Wind turbines on the island of Vinalhaven, ME, were retrofitted with serrated edges as part of an effort to reduce noise impacts on neighbors…. No formal study of the effects has yet been released, though neighbors report that the serrations seemed to moderate the lower-frequency thumping element of the sound, while slightly increasing the overall whooshing aspects, as the studies summarized in Barrone might suggest (personal communications, 2012).
Meanwhile, at Europe’s Wind Energy Association conference in Barcelona this year, Philip Totaro spoke for the industry in noting:
“A multitude of technologies have been prototyped for low noise but commercial use is limited except in cases where regulations have required it. Technical solutions could be used in combination, but effects have not been comprehensively studied and data is limited. For blade noise, the serrated trailing edge has been the single most influential technology, but others contribute as well. Turbine controls to derate when noise exceeds a threshold are a simple and cheap solution, but come at the expense of energy loss.”