Quantifying the environmental impact of underwater noise from tidal stream turbines

Expanding the evidence base

The different ways in which tidal turbines might interact with the marine environment is of ongoing interest to regulators, project developers, and coastal communities. One key area of interest relates to noise produced during installation and operation of tidal energy converters and the effects this might have on marine wildlife.

The lack of scientific data on the noise generated by tidal turbines and uncertainty about its effects on marine wildlife could cause problems and delays in consenting for future tidal energy developments. To address this, ORE Catapult’s Marine Energy Engineering Centre of Excellence (MEECE) partnered with world-leading tidal developer Nova Innovation, and Seiche Ltd  – the UK’s leading specialist in underwater noise and marine mammal monitoring – on a collaborative project to measure the underwater sound levels from Nova Innovation’s subsea tidal turbines. The team’s collective goal? To strengthen the evidence base and address key uncertainties surrounding environmental impact assessments for tidal energy projects.

Edinburgh-based Nova Innovation (Nova) specialises in technology and project development for tidal stream and floating solar energy, working with clients across three continents. Of approximately 16 offshore tidal stream turbines deployed around the world, six have been designed and manufactured by the Nova team in Scotland.

Partnerships with industry leaders such as Nova illustrate how supportive collaboration can deliver outstanding results designed to accelerate, derisk and reduce costs for innovative technologies while helping to share knowledge and learning to benefit the wider renewable energy industry.

 

Harnessing data to establish the facts

In February 2023, the team carried out noise measurements at Nova’s Shetland Tidal Array in Bluemull Sound, Shetland. Installed in 2016 this was the world’s first offshore tidal array, which has since generated in excess of 52,000 hours of clean energy from the predictable power of the tides.

The team’s measurement protocol followed standards  set by the International Electrotechnical Commission (IEC) which provide uniform methodologies to ensure consistency and accuracy in the measurement and analysis of acoustical emissions from marine energy converters, including tidal turbines[i].

Retaining the flexibility required for working in challenging tidal sites, elements were factored in to gather data to enable better understanding for:

• Potential collision risk between marine wildlife and rotating turbine blades – despite no collisions having been observed to date, and currently-available evidence suggesting that actual risk levels remain lower than perceived risk[ii].
• Noise levels produced during installation and operation of tidal energy converters, and their potential impact on local marine wildlife.

 

Credit: Nova Innovation

Capturing live turbine data

A drifting hydrophone was deployed from a rigid inflatable boat (RIB) to record underwater noise levels from a series of subsea locations as the boat travelled across the test area. All acoustic measurements were taken across the array during spring tides at both ebb and flow while Nova’s control centre operatives manipulated the array’s energy outputs remotely from their HQ in Edinburgh to allow sound level recordings of turbines operating both individually and collectively.

The team gathered sufficient data to characterise sound pressure levels at different power outputs for individual turbines and the full six-turbine array. They also recorded background noise in and around the array area in Bluemull Sound.

The acoustic model produced using the noise measurements predicted an area approximately 100 metres from the tidal array where overall sound levels were found to exceed 120 dB – the disturbance threshold for marine mammals identified by the US National Marine Fisheries Service (NMFS)[iii] and used as an industry standard limit for continuous noise.

 

Conclusions

The results of this collaborative effort indicate that acoustic injury to marine mammals is highly unlikely, even after prolonged exposure in close proximity to turbines. Some minor behavioural disturbance may be possible at close range to turbines, but it is unlikely that significant disturbance would result. This supports existing research suggesting that marine animals are able to detect turbines, and exhibit avoidance or evasion behaviours thereby reducing the risk of collision[iv].

Commenting on the collaboration with ORE Catapult,  Dr Gavin McPherson, Associate Director, Nova Innovation said:

“Nova Innovation and ORE Catapult have a long-standing working relationship. The Catapult team was one of a consortium of nine European organisations in the €20m Horizon 2020 EnFAIT (Enabling Future Arrays in Tidal) project led by Nova which successfully completed in June 2023.

“The flagship project, focused on Nova’s Shetland Tidal Array in Bluemull Sound, delivered a 41% reduction in the cost of tidal stream energy – demonstrating bankability and building investor confidence in the sector. ORE Catapult’s support to Nova Innovation throughout EnFAIT played a key role in this major achievement.”

 

Nova Innovation: Next steps

Building on the success of the company’s Shetland Tidal Array, Nova has won European Union funding for a 4 MW tidal energy farm that will be home to the largest number of tidal turbines anywhere in the world, at the European Marine Energy Centre’s Fall of Warness tidal site in Orkney.

Nova’s team will lead the pan-European SEASTAR consortium, funded by the EU’s Horizon Europe programme, which aims to showcase the viability of a sustainable large-scale  tidal energy farm and accelerate mass manufacturing of tidal turbines at Nova’s headquarters in Edinburgh.

The SEASTAR project, unveiled at COP28, reinforces the collaborative partnership between Scotland and our European partners. With stated aims including pioneering a green marine energy revolution and catalysing the creation of high-quality green jobs, SEASTAR represents an important step towards unlocking a global source of renewable energy.

 

 

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[i] IEC Technical Specification 62600-40:2019. Marine energy – Wave, tidal and other water current converters – Part 40: Acoustic characterization of marine energy converters.

 

[ii] Nova Innovation (2023). Shetland Tidal Array Monitoring Report April 2022 to July 2023. STA-002. Available at: https://marine.gov.scot/node/23283

 

[iii] Southall, B.L., Finneran, J.J., Reichmuth, C., Nachtigall, P.E.,  Ketten, D.R. Bowles, A.E., Ellison, W.T., Nowacek, D.P., and Tyack, P.L. (2019). Marine Mammal Noise Exposure Criteria: Updated Scientific Recommendations for  Residual Hearing Effects. Aquatic Mammals 45(2), 125-232, DOI 10.1578/AM.45.2.2019.125

 

[iv] Risch, D., van Geel, N., Gillespie, D., & Wilson, B. (2020). Characterisation of underwater operational sound of a tidal stream turbine. The Journal of the Acoustical Society of America, 147(4), 2547–2555.

 

Gillespie, D., Palmer, L., Macaulay, J., Sparling, C., & Hastie, G. (2021). Harbour porpoises exhibit localized evasion of a tidal turbine. Aquatic Conservation: Marine and Freshwater Ecosystems, 31(9), 2459–2468. https://doi.org/10.1002/aqc.3660

 

Palmer, L., Gillespie, D., MacAulay, J. D. J., Sparling, C. E., Russell, D. J. F., & Hastie, G. D. (2021). Harbour porpoise (Phocoena phocoena) presence is reduced during tidal turbine operation. Aquatic Conservation: Marine and Freshwater Ecosystems, 31(12), 3543–3553. https://doi.org/10.1002/aqc.3737