On behalf of SEAS, Ødegaard & Danneskiold-Samsøe (ODS) has performed and investigation of the underwater noise emitted by existing offshore wind turbines. The purpose of the investigation was to estimate the expected underwater noise emitted from the planned offshore wind turbine parks consisting of 2 MW wind turbines.
The results of the investigation will be included as part of the background material of a VVM report (Environmental Impact Report) for proposed offshore wind turbine parks.
The investigation is based on measurements of underwater noise from offshore wind turbines with two types of foundation. The first type is a concrete foundation, which is placed on the seabed (Vindeby, Denmark). The second type is called a "monopile" foundation. In this case, the foundation is a steel pipe that has been driven into the seabed (Gotland, Sweden). Because underwater noise from the wind turbine is emitted from the foundation to the water, two different types of offshore wind turbines foundations were measured to assess possible differences in noise emission.
The noise levels from the wind turbines was compared to the ambient noise (the background underwater noise) by performing noise measurements whilst the wind turbines were operating and whilst stopped. The frequency range used in the investigation has been selected to include the known frequencies that are audible for the appropriate sea animals.
The existing offshore wind turbines have the power of 500 kW. The proposed offshore wind turbines will have the power of 2 MW. To estimate the noise emitted from the future planned, more powerful wind turbines, vibration measurements were performed at the foundations of the offshore wind turbine and compared to similar vibration measurements performed on a 2 MW wind turbine running on land.
The result of the investigation is an estimate of the underwater noise, which can be expected from the 2 MW offshore wind turbines. These results are subsequently going to form a base of the evaluation of the effect on the animal life.