Floating Offshore Wind Sound Analysis

DeepCwind is a consortium that is planning to launch two direct drive 6 MW Goldwind turbines inside state waters, about 2.8 miles south of Monhegan Island, Maine. The island is home to full-time residents who have expressed interest in the noise effects of the project. To address this issue, the air-based sound attenuation surrounding the site was modeled using WindPRO software. WindPRO software has an extensive database of information on wind turbines from many companies. Unfortunately, most of the information is for smaller turbines, with very few large turbines. The Goldwind 6 MW turbines are not in the system because they are a new design and no data are available for the noise levels at different wind speeds, but there were also no other 6 MW turbines in the database. To estimate the potential noise for residents, the sound propagation for two 5 MW turbines and a 7.5 MW turbine were modeled instead. Both the Goldwind turbine and the 7.5 MW Enercon turbines are direct drive, which reduces the noise by eliminating the gearbox mechanical noise. However, the two 5 MW turbines available in the WindPRO database are geared. WindPRO used generic octave data for all three turbines, tailored to the recorded noise output levels of a typical turbine. The three turbines can provide a range of possible sound levels from the Goldwind 6 MW turbines through comparison.

 

The analysis showed that the sound levels for all turbines modeled were around 35 dB at the southernmost edge of Monhegan Island. To put this in context, 35 dB is slightly above a whisper and 50-60 dB is a typical conversation. The results even fall below the typical range of sound from ocean waves, between 40-80 dB depending on the frequency and sea state. As the sound waves travel across the island, the level will continue to significantly decrease before reaching main residential areas.

 

While the turbines may be acceptable to the people living nearby, the effect on marine mammals is still largely unknown. The process of pile driving has been shown to temporarily drive away animals, but the use of a floating platform is less invasive than seabed installation and the platforms will be in a very different deep-water environment. The concern then switches to the operational stage of the wind turbines, which will first require underwater noise output data from operating floating turbines and a complete profile of ambient noise before and after the project is installed. Turbine noise could potentially mask animal sounds and inhibit tasks such as echolocation, navigation, communication, evasive maneuvers, and feeding. These studies will provide the basis for understanding sound effects on marine mammals.

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