Logo: to the web site of Uppsala University

This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

The operation of Wave Energy Converters (WECs) will add to the anthropogenic impact on the marine environment. Underwater radiated noise is one suggested impact. To estimate if there might be an impact on the environment, the noise must be characterized. Noise from two full scale WECs was measured in 2013. The purpose of this study was to examine the change in noise levels from the WECs in different significant wave heights and wave Steepness, propagation loss and the significance of a noise dampening feature. Noise was measured simultaneously at two distances (1m and 150 m). Noise levels at 1m varied between 108-143 dB re 1 µParms in Hs 0.09-2.84m. The noise dampening feature had a significant impact on the noise levels. Noise levels increased logarithmically in relation to Hs and linearly in relation to α2. α2 was found to be an uncertain variable when used alone to estimate noise levels.

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 chemicals 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 perceive sound between marine organisms, one sound that is clearly 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 WECs 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 bulk of the energy in frequencies <1 kHz). The SPL of the radiated noise fluctuated significantly, depending on wave height. Broadband SPL_rms 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 propagation loss. The noise is not expected to have any negative effects on behaviour 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.

Wave energy conversion is a clean electric power production technology. During operation there are no emissions in the form of harmful gases. However there are unsolved issues considering environmental impacts such as: electromagnetism; the artificial reef effect and underwater noise. Anthropogenic noise is increasing in the oceans worldwide and wave power will contribute to this sound pollution in the oceans; but to what extent? The main purpose of this study was to examine the noise emitted by a full scale operating Wave Energy Converter (WEC) in the Lysekil project at Uppsala University in Sweden. A minor review of the hearing capabilities of fish and marine mammals is presented to aid in the conclusions of impact from anthropogenic sound. A hydrophone was deployed to the seabed in the Lysekil research site park at distance of 20 and 40 m away from two operational WECs. The measurements were performed in the spring of 2011. The results showed that the main noise was a transient noise with most of its energy in frequencies below 1 kHz. These results indicate that several marine organisms (fish and mammals) will be able to hear the operating WECs of a distance of at least 20 m.

Field measurements of the hydroacoustic noise from Wave Energy Converters (WECs) in the Lysekil project at Uppsala University and the Project WESA (joint effort between Uppsala University (Lead Partner), Ålands Teknikkluster r.f. and University of Turku) are presented. Anthropogenic noise is increasing in the oceans world wide and wave energy conversion may contribute to this noise, but to what extent? The main objective in this study is to examine the noise from full scale operating WECs in the Lysekil and project WESA. Acoustic measurements were made in order to be able to estimate potential environmental impact. Submersible recording devices (SRD) were deployed at 1 m from WECs at a depth of approximately 24 meters. Both WECs are a full scale point absorber with a directly driven linear generator, placed on gravitation foundations at the seabed with a connected buoy at the surface that absorbs energy from the heaving waves. The SRDs used to measure the noise from the WECs, consists of a SM2-recorder from Wildlife Acoustics and hydrophones from High Tech Inc. (HTI 96 MIN and HTI 99 HF). Measurements at in the Lysekil project were carried out in the spring of 2013 and in the project WESA in Jan-Feb of 2012. Preliminary results show that the main operating noise radiated from the WEC are short transients with instant rise time when the translator moves past the stator and when the stator hits the end stop springs of the generator. Most of the power in the noise is between 20 – 1000 Hz.

Wave energy conversion is a potentially clean and sustainable form ofenergy conversion with no emissions of gases or liquids during operation.There are other environmental issues that need to be taken in consideration.The deployment of a wave power farm will contribute with new surface formarine organisms to colonize. Submerged structures attract marineorganisms, both sessile and mobile. This has been observed on thegenerators in Lysekil project, this is called reef effect. Several marineorganisms have sensory systems that allows them detect electromagnetism.If the electromagnetism in the generators and sea cables will have an impacton these organisms is yet to be studied. Underwater noise is another topicthat needs to be concerned. This thesis presents a study on underwater noisefrom a full scale Wave Energy Converter (WEC) in the Lysekil Project.A hydrophone measured the underwater noise emitted from operatingdirect driven linear Wave Energy Converters in the spring of 2011. The mainpurpose was to study the emitted noise from an operating WEC, to determinecharacteristics such as spectrum levels, Sound Pressure Level (SPL), pulseduration and repetition rate.The results showed that the main noise is a transient noise with most of itsenergy in frequencies below 1 kHz. These results indicate that severalmarine organisms (fish and mammals) will be able to hear the operatingWECs. Although no behavioural reactions or injuries due to high soundpressure levels (SPLs) are expected.