The conversion of wave energy into electrical energy has the potential to become a clean and sustainable form of renewable energy conversion. However, like all forms of energy conversion, it will inevitably have an impact on the marine environment, although not in the form of emissions of hazardous substances (gases, oils, or checmicals associated with anticorrosion. Possible environmental issues associated with wave energy conversion include electromagnetic fields, alteration of sedimentation and hydrologic regimes and underwater radiated noise.
Underwater noise has the potential to propagate over long distances and thus have the potential to disturb marine organisms far away from the noise source. There is great variation in the ability to pervieve sound between marine organisms, one sound that is cearly audible to one species can be completely inaudible to another. Thus, to be able to determine potential environmental impact from WECs associated with underwater noise, the noise radiated from the WECs must be known. This thesis presents results from studies on the underwater radiated noise from four different full-scale WEBs in the Lysekil Wave Power Project.
Hydrophones were used to measure the underwater radiated noise from operating point absorbing linear WECs. The main purpose was to study the radiated noise from the operating WECs with emphasis on characteristics such as spectrum levels, Sound Pressure Level (SPL), noise duration and repetition rate. This to be able to determine the origin of the noise and if possible, implement design changes to minimize radiated noise.
The results identified two main operational noises (transients with the bull of the energy in frequencies <1 kHz). The SPL of the radiated noise fluctuated significantly, depending on wave height. Broadband SPLrms of the measurements ranged between ~110 dB and ~140 dB re 1 μPa and SPL peak of specific noises ranges between ~140 and ~180 dB re μPa. Audibility was estimated range from 1km to 15 km depending critically on species and on assumptions of propogation loss. The noise is not expected to have any negative effects on hebaviour or mask any signals, unless in the vicinity (<150m) of the WECs in significant wave heights. No physical damage, even in close vicinity are expected on either fish or marine mammals.
Having the aim to have as little impact on the environment a possible, these studies are important. This way precautions can be implemented early in the technical development of this kind of renewable energy converters. The benefits from the WECs the Lysekil wave power project are believed to outweigh possible environmental impacts due to underwater radiated noise.