Ireland is the fifth most attractive country to invest in renewable energy projects on a GDP-normalised basis (EY June 2024) and is aiming for 5GW of offshore wind power by 2030. A significant challenge in delivering this is the planning process for major infrastructure, write Eugene McKeown and Dr Eoin King, University of Galway.
The planning/permitting process for offshore wind power has three significant EU requirements that need to be considered:
- Directive 2011/92/EU (as amended by Directive 2014/52/EU) relating to the environmental assessment of projects;
- Regulation 2022/2577 introducing a rebuttable presumption that renewable energy projects are of overriding public interest for the purposes of the relevant environmental legislation, and
- Directive 2023/2413 setting a target of up to 45% energy from renewable sources by 2030.
Maritime Area Consents1 have now been granted for six offshore wind projects in Ireland, and planning applications for some of the projects have recently been submitted. Some details of the scale of the projects are illustrated in Table 1.
Conventional wisdom has focused on the distance from the shore to mitigate the noise from offshore wind turbines, but this approach has failed to explore the potential impacts on coastal soundscapes.
A considerable body of research has investigated noise from onshore wind turbines. However, important questions relating to offshore wind turbines, such as sound2 propagation over water and the sensitivity of the soundscape remain unanswered.
The Galway Sound Lab research group at the University of Galway is examining these issues, including modelling offshore wind turbine noise propagation and soundscape studies.
Environmental impact assessment
Environmental Impact Assessments (EIA) in the planning process are instruments for balancing the economic, social and environmental dimensions of a project.
Installations for the harnessing of wind power for energy production with more than 25 turbines or 50 megawatts are considered strategic infrastructure and applications including an EIAR, are submitted directly to An Bord Pleanála.
The key document in the EIA process is the Environmental Impact Assessment Report (EIAR), which is drafted by the developer. Offshore wind turbines, on the scale proposed, inevitably include some uncertainty regarding environmental impacts. This is evidenced by the ‘Marine Flexibility Option’ process adopted by An Bord Pleanála for offshore wind applications.
All stakeholders (developers, affected parties, statutory consultees, regulators and consenting authorities and consultants/advisers) have an interest in minimising the risks within the EIA process. Should the risk of an impact be ignored or inadequately assessed it can have detrimental consequences for the project, the stakeholders and future similar projects.
The preamble to the 1985 EIA Directive (CEC 1985) stated that:
‘the best environmental policy consists in preventing the creation of pollution or nuisances at source, rather than subsequently trying to counteract their effects’.
Data and information included by the developer in the EIAR, in accordance with Annex IV to Directive 2011/92/EU, should be:
‘complete and of sufficiently high quality’.
The contents of an Environmental Impact Statement, now an EIAR, to be submitted with the planning application are further set out in the Planning and Development Regulations 2001, ie, ‘the data required to identify and assess the main effects which the proposed development is likely to have on the environment’.
The Environmental Protection Agency (EPA) has drafted guidelines for compliance with Directive 2011/92/EU for all EIARs undertaken in the state.
A summary of the information relating to noise provided in the EIARs submitted to date is shown in Table 2.
The EIAR must include (inter alia):
- Project description;
- Description of the baseline environment;
- Assessment of the impacts by: A/ Quantifying the potential effect; and B/ Assessing the impact by considering the magnitude of the change and the sensitivity of the receptor.
The EPA guidelines describe the project description and the baseline as the:
‘factual foundations of the EIAR’ and go on to state that:
‘the main purpose of an EIAR is to identify, describe and present an assessment of the likely significant effects of a project on the environment’.
The obligation on the developer to be transparent with the information provided in the EIAR is further amplified in the guidelines:
‘Furthermore, there are increased social and legal emphases on the need for meaningful public participation in decisions relating to environmental issues. In this context, it is more important than ever to ensure that information is available in a format that is clear, concise and accessible to the greatest number of people – and certainly to a wider audience than the professional’.
Marine flexibility option
One of the difficulties with the planning system (as interpreted by the courts) is the requirement for precise descriptions and measurement.
Projects are considering a two/three-year period for planning permission, with a further two/three years before commissioning, so on average over five years between planning and operation.
In that time technology will have developed, and a five-year-old planning application may not be flexible enough to cater for all eventualities. Developers are therefore submitting project design options, for example two turbine sizes or different turbine layouts as part of a single EIAR.
Flexibility in the design and the level of detail to be provided in an EIAR is being addressed through an application to the board under Section 287A of the Planning and Development Act 2000.
Unfortunately, this ‘flexibility’ may have led to an omission of important information in some of the planning applications submitted to date. On review of these applications, the Operational Noise section in one of the EIARs is limited to the following sentence:
‘No likely significant effects are predicted from the offshore WTG3s’,
without providing any evidence to support this statement. Another EIAR states that the turbine noise source level data cannot be provided in the EIAR because of:
‘non-disclosure agreements’.
This lack of transparency on the data used for noise modelling predictions undermines the confidence that other stakeholders can have in the EIAR.
Baseline environment
The EIA Directive requires:
‘A description of the relevant aspects of the current state of the environment (baseline scenario)’.
The baseline should include details on the context, character, significance and sensitivity of the baseline in the study area.
For offshore wind farms the study area could extend many kilometres inland from the coast (King & Ní Bhraonáin 2023). Noise propagating from an offshore wind farm attenuates 3-6 dB with a doubling of distance. If the offshore turbines are 10km from the coast and result in a noise level of 35 dB(A) at the coast, the noise level attributable to the wind farm 10km inland is potentially greater than 30 dB(A).
Coastal areas are generally noisy close to the shore due to surf noise. This attenuates rapidly with distance, and it is not unusual to measure noise levels between 20 and 25 dB(A) at quiet rural areas inland.
Data in one of the EIARs submitted shows measured levels between 20 and 30 dB(A) at wind speeds of up to 10 m/s. The clustering of the data around 22 dB(A) indicates that the baseline noise levels were even lower but could not be quantified due to the noise floor of the measuring equipment.
Only two of the four EIARs submitted to date carried out any baseline noise measurements at locations impacted by operational wind turbine noise. Without a baseline it is not possible to assess an effect.
Assessment of the effects
The EIAR focuses on the effects that are both ‘likely and significant’ and a description of the effect that is ‘accurate and credible’ according to the EPA guidelines. From data provided in the EIARs we can see that low baseline noise levels arise at inland locations in the study areas.
Three of the proposed offshore wind farms are located off the Dublin/Wicklow coast. Because of their proximity to each other, it is necessary to assess the cumulative wind turbine noise impact when the three wind farms are operating. This has been calculated in only one of the EIARs submitted. The cumulative operational noise level has been calculated at two different locations to be 34 dB(A).
In each of the four EIARs for proposed offshore wind farms the conclusion in the Noise and Vibration chapter is that operational noise will not have a ‘significant impact’. In each case a threshold of 35 dB(A) is taken as a threshold below which no significant effect occurs. This approach is justified in the EIARs as complying with the Wind Energy Development Guidelines (WEDGS 2006) and/or ETSU-R-96 (UK guidance).
The Irish (WEDG 2006) and UK (ETSU-R-97) guidelines refer to 35 dB(A) being sufficient to protect amenities while not unduly restricting wind energy developments ‘which should be recognised as having wider national and global benefits’. This balance reflects the requirements of Regulation 2022/2577 and Directive 2023/2413 referred to earlier.
Strict compliance with the WEDGS 2006 is one way of setting a threshold for significance. It may not however be definitive, given the recent High Court decision in the Meenacloghspar wind farm case4. In that case a precedent was set where reliance on a grant of planning permission was not a sufficient defence to a private nuisance action. Justice Egan stated:
‘The defendant cannot rest its laurels on the proposition that the generation of renewable energy is a socially valuable activity which it is in the public interest to continue. There is not a binary choice to be made here between the generation of clean energy by the wind farm, and a good night’s sleep for its neighbours. It should be possible to achieve both.’
It has been demonstrated that there are quiet areas (~20 dB(A) background noise level) close to the coast. With offshore wind farms being designed to meet a noise threshold of 35 dB(A) at the coast, it is foreseeable that there will be locations that a noise level increase of 10 to 15 dB(A) above background level will occur.
ETSU-R-97 (and WEDG 2006) both refer to a common perception that a 5 dB(A) increase above background noise level is ‘tolerable’. Tracing the historical development of this 5 dB threshold leads to BS 4142:1990 where 5 dB(A) was considered ‘of marginal significance’. BS 4142 does not specifically exclude wind turbine noise but defers to:
‘other sources falling within the scopes of other standards or guidance’.
and states:
- A difference of around +10 dB or more is likely to be an indication of a significant adverse impact, depending on the context.
- A difference of around +5 dB is likely to be an indication of an adverse impact, depending on the context.
The UK Design Manual for Roads and Bridges LA 111 Noise and vibration (DMRB) proposes that up to 3 dB(A) a change in road traffic noise is negligible and a change of up to 4.9 dB(A) is minor in the long term.
The EPA Guidance note for noise NG4 sets out criteria for quiet area screening. In such areas, NG4 sets very stringent noise criteria for EPA licensed sites such as:
‘the noise from anthropogenic sources should not be clearly audible’,
This results in a recommendation that noise from the licensed site to be at least 10dB below the average background noise level measured during the baseline noise survey. A separate threshold is set for ‘Areas of Low Background Noise’.
While addressing different noise sources there is significant weight behind a 5 dB(A) change as being of moderate significance apart from any fixed limit guideline.
What can we do?
The Aarhus Convention5 has an objective to guarantee rights of public participation in decision-making in environmental matters.
Research has shown that social acceptance of wind energy development is related to a wide range of actual, potential or perceived impacts of a wind energy project.
The issue of trust has a key role in shaping social acceptance. An important aspect of gaining trust is openness and transparency in the EIA process. One Danish report (Clausen et al. 2021) criticises ‘promoters using a ‘present and defend’ approach to noise, where they attempt to counter people’s feelings about noise with technical facts and a demonstration of the fulfilment of regulations’.
A lay person’s reading of ‘No likely significant effects’ could, not unreasonably, equate to meaning that the turbines will not be audible. In a scenario where wind turbine noise could be 15 dB(A) above background levels this would obviously not be the case.
Figure 1 is taken from EPA NG4 2016 and provides a method to determine the significance of an impact from the magnitude of the effect and the sensitivity of the receptor. This technique is common practice in EIARs in Ireland.
Figure 1: Typical Classifications of the Significance of Effects (EPA NG4 2016).
Figure 1 illustrates a classification of significant effects using a description of the effects under specific headings, ie character, magnitude, duration, probability, consequences, and the significance and sensitivity of the existing environment.
The soundscape
EIA practice to date has focused on the magnitude of the change. Limited attention has been paid to the change in character of the noise. To improve this methodology, an additional assessment on the effects of the soundscape could be carried out. The soundscape assessment would provide a more holistic approach and indicate any potential impact in a transparent manner.
The ISO 12913 series of standards are in development and have not yet been deployed in an EIAR context. Further research and development may be required before they would be of practicable use. Nonetheless the ISO 12913 soundscape standard attributes and the circumplex model have a value in quantifying effects on the soundscape.
The circumplex model is shown in Figure 2. The X (Annoying – Pleasant) axis is of particular significance as in ‘Quiet Areas’ the background noise is likely to be dominated by the sounds of nature or domesticated animals. Such sounds are generally regarded as ‘pleasant’.
A change where wind turbine noise replaces the sounds of nature is likely to result in a shift to the left along this axis. In the event of noise characteristics such as tonal noise or amplitude modulation occur, this shift will be exacerbated.
Figure 2: Circumplex model from ISO 12913-3.
The magnitude of the effect includes the spatial extent of the effect. Standard EIAR practice is to develop a noise propagation model to predict this extent. The modelling of airborne noise from offshore wind turbines is still in development.
Noise propagation over water is limited to a few studies and no international standard propagation model has been developed. Model inputs such as the noise source level of the turbines need to be clarified as the source level has a direct bearing on the level at the receiver. As outlined in Table 2, this information is not provided in two of the EIARs submitted to date.
Modelling and assessing the impacts
Current best practice for modelling onshore wind turbine noise adds 2 dB(A) for uncertainty to the source level, unless the source level is a warranted level or the uncertainty is stated by the manufacturer. It is arguable that a larger uncertainty may be needed for offshore wind turbines.
Where wind turbine noise has been modelled (in three of the four published EIARs) reference is made to a worst-case scenario, where the model is based on downwind conditions.
Wind turbine noise levels at the receiver locations would be expected to be lower in cross-wind and upwind conditions. Two of the four published EIARs include Wind Rose figures showing wind velocity, neither state the measurement period or the measurement height on which the data is based.
Baseline measurement data could be used to estimate the frequency/probability of occurrence. It should be noted that the wind velocity (speed and direction) at hub height offshore may be significantly different from the wind velocity onshore at the receptor location. Conditions can arise where a significant onshore wind at hub height coincides with low or no wind onshore.
A wind rose with one (or more) year’s data could provide an estimate of how often the modelled conditions will arise. The duration and frequency of wind turbine noise levels higher than background levels could then be estimated. EPA Guidance provides language to describe temporal effects in a consistent manner.
The sensitivity of the receiving environment needs to be evaluated using the context and character of the area, ie, is it an isolated residence, a significant residential area, a national park or a UNESCO world heritage site? Is it a recreational/tourist area with higher background noise levels at particular times of the year? Would the proposed change in noise level impact a particularly sensitive receptor?
In determining the overall significance of wind turbine noise a distributional impact matrix can broadly identify the extent of the impact and the number of locations impacted by it.
Large offshore wind projects will have varying spatial impacts due to the scale of the projects and the wind/weather conditions. A weighted matrix could address the issue of different receiver sensitivities.
Summary
Ireland is entering a crucial phase in the development of offshore wind energy projects. Four EIARs have been published to date. All the published EIARs are claiming no significant noise impact based on a 35 dB(A) threshold onshore.
The data provided in some of the EIARs is not transparent, ie, there is a lack of baseline noise monitoring data, lack of source level data used in the modelling and in some cases definitive assertions are not supported with evidence.
Where data has been provided, it is clear that offshore wind turbines will be audible under certain weather conditions onshore. The impact on the soundscape is likely to be intermittent and negative and this should be considered in the context of the overall environmental impact of the project
In Ireland, there are clear examples of how a failure to account for noise impacts in the planning process can have serious consequences, most notably the case of Dublin airport’s second runway.
In this case noise issues were not comprehensively considered in the initial planning stage, and severe restrictions were placed on its operation at night (An Bord Pleanála 2007). It is clear that a failure to properly assess noise impacts can lead to a significant under-utilisation of resources, or force expensive retrofitted solutions.
Including a soundscape assessment in the EIA provides transparency and clarity in the process and reduces risk to the developer. Failure to do so risks reputational damage to an important industry and delays in the approval process for future projects.
Authors: Eugene McKeown has qualifications in mechanical engineering, acoustics and environmental law, is an Engineers Ireland Fellow and has more than 40 years of experience on the effects of noise and vibration. He has served on International Standards Organisation, International Electrotechnical Commission and International Energy Agency technical committees relating to noise. His work includes modelling and measuring environmental noise from wind farms, roads, ports, railways and industrial sites. He is currently a doctoral researcher at the University of Galway investigating the extent to which noise from offshore wind turbines could impact the soundscape on the Irish coast.
Dr Eoin King is a lecturer and programme director of mechanical engineering at the University of Galway. Currently. He is vice president of the International Institute of Noise Control Engineering and is a member of the European Commission's Noise Expert Group. With extensive expertise in environmental acoustics and noise control, he has authored or co-authored more than 100 academic journal articles, book chapters, conference papers, and reports. From 2013 to 2021, Dr King was a professor of acoustics at the University of Hartford in Connecticut, USA. Upon returning to Ireland in 2021, he founded the Galway Sound Lab, where he currently serves as director.
References & bibliography
6) An Bord Pleanála (2007), Reference Number: PL 06F.217429
7) BS 4142:2014+A1:2019, Methods for rating and assessing industrial and commercial sound
8) Clausen, N.-E., Rudolph, D., Kirch Kirkegaard, J., & Larsen, S. V. (2021). Where to put wind farms? Challenges related to planning, EIA, noise and social acceptance. Danmarks Tekniske Universitet, Denmark. https://doi.org/10.11581/DTU.00000205
9) Directive 85/337/EEC on the assessment of the effects of certain public and private projects on the environment, Council of the European Communities, http://data.europa.eu/eli/dir/1985/337/oj/eng
10) Directive 2011/92/EU, on the assessment of the effects of certain public and private projects on the environment (codification), European Union 2011. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32011L0092
11) Directive 2014/52/EU of the European Parliament and of the Council of 16 April 2014 amending Directive 2011/92/EU on the assessment of the effects of certain public and private projects on the environment, European Union 2014. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A32014L0052
12) Directive (EU) 2023/2413 amending Directive (EU) 2018/2001, Regulation (EU) 2018/1999 and Directive 98/70/EC as regards the promotion of energy from renewable sources, and repealing Council Directive (EU) 2015/652, European Union 2023, https://eur-lex.europa.eu/legal-content/EN/NIM/?uri=CELEX:32023L2413
13) EPA NG4 2016, Guidance Note for Noise: Licence Applications, Surveys and Assessments in Relation to Scheduled Activities (NG4). https://www.epa.ie/publications/monitoring--assessment/noise/NG4-Guidance-Note-(January-2016-Update).pdf
14) ETSU-R-97, the Assessment and Rating of Noise from Wind Farms, Final ETSU-R-97 Report for the Department of Trade & Industry. The Working Group on Noise from Wind Turbines, 1997. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/49869/ETSU_Full_copy__Searchable_.pdf
15) EY (June 2024), Renewable Energy Country Attractiveness Index (RECAI). https://www.ey.com/content/dam/ey-unified-site/ey-com/en-gl/insights/energy-resources/documents/ey-gl-recai-63-final-07-2024.pdf
16) King E.A. (2019), A balanced approach to aircraft noise management: The curious case of Dublin Airport’s new runway, Proceedings on INTER-NOISE 2019, June, Madrid Spain,. https://www.sea-acustica.es/INTERNOISE_2019/Fchrs/Proceedings/1960.pdf
17) King E.A., Ní Bhraonáin, L., (2023), Evaluating the potential impact of noise annoyance from offshore wind turbines in Ireland, Forum Acousticum, Turin 2023. https://appfa2023.silsystem.solutions/atti/000634.pdf
18) S.I. No. 600/2001 - Planning and Development Regulations, 2001
19) Wind Energy Development Guidelines, 2006, Department of the Environment, Heritage and Local Government.