Abstract
This deliverable contains the methodology and results from Task 2.3 of SafeWAVE project (Acoustic Monitoring), which essentially is about the acquisition of acoustic, sea state and operational data in four wave energy converter (WEC) prototype test sites. Monitoring campaigns were carried out during non-operation and operational regimes, in order to obtain underwater Sound Pressure Levels for a range of sea states and frequencies. The final goal is to characterize the acoustic signature of the WEC prototypes.
First, for Aguçadoura (Portugal) test site two pre-installation monitoring campaigns were carried out in January and May 2022. Median SPL values were found to be between 75 and 105 dB re 1 μPa (for the lowest end of the spectrum and the band centred around 200 Hz, respectively). The state of the sea is most reflected on the high frequencies 4 kHz and 10 kHz for the January and May campaign, respectively, as well as on the 100 Hz band for the latter. A first commissioning campaign was performed in September 2023, where some differences were (+10 dB re 1 µPa) found for the wave heights bin [2, 2.5). However, due to the short campaign duration (9 days), and this campaign happening during the commissioning of the device (meaning that it’s not fully representative of the WEC real operational state, as its forced between states), no concluded results should be extracted.
Second, for the BiMEP test site (Spain), two monitoring campaigns were undertaken: pre/installation and post-installation (of the PENGUIN II WEC). For the first one, an increase of more than 15 dB re 1 μPa is found for high wave heights after the deployment of the mooring lines of the WEC, with increases of up to 20 dB re 1 μPa during the installation period. The higher differences in SPL between the background noise levels are found in the lower frequencies.
The results from the post-installation campaign data indicate that there exists some contribution from the device to the background noise levels, especially in the lower frequencies. These occur when comparing the On and Off states SPL distributions with respect to those of the Uninstalled periods (in fact, the comparison between On-Off SPL show no significant differences). These differences can be up (in median value) to 28 dB re 1 μPa for the lowest frequencies (decreasing approximately linearly with frequency). In addition, during the decommissioning of the device, noise levels were the highest found in the campaign, with values over 120 dB re 1 μPa (centred around 300 Hz). It is worth noting that mooring lines were also detectable above background noise for rough sea states around the 3 and 4 kHz bands.
Third, for Mutriku (Spain), one monitoring acoustic campaign was undertaken during March-April 2022. No contribution to the background soundscape from the WEC was found from our analysis. This was inferred comparing day and night SPL distributions as well as carrying out a causality test that showed no link between operational status of the power plant and the SPL time series for any frequency.
Lastly, in the SEM-REV test site (France), one monitoring acoustic campaign was undertaken during July-August 2021. The analysis indicates no significant contribution of the WEC to the ambient noise (WAVEGEM by GEPS Techno), although it must be noted that the study was limited by the scarcity of operational data of the WEC device. Additionally, as in the BiMEP test site, mooring lines could be detected above background noise as a peak centred in 4 kHz that increases with wave height. Finally, the highest values in SPL are localized in a narrow band centred in 30 Hz, with values reaching almost 120 dB re 1 μPa. This narrow peak could be caused by the WEC, when forced by strong waves, but without more operating data or a baseline campaign this remains a hypothesis.