Planning policy is evolving to address wake loss risk for offshore wind projects

Wake loss, or wake effects, occurs when upstream turbines reduce wind speed and increase turbulence impacting the performance of downstream turbines. It sometimes means one wind farm can lose out on available wind speed, and is therefore able to generate less energy, due to the effect of another.

While fresh studies are being undertaken to better understand wake loss and how it can be mitigated, a report by Tamarindo published earlier this year highlighted a 2022 study by scientists at the University of Bergen which found that wake loss as a result of one wind farm could be experienced at another up to 50 miles away.

Wake loss disputes have already arisen between developers behind wind farms in UK waters and, in the context of UK government policy to scale up offshore wind generation capacity to up to 50GW by 2030 and associated increasing spatial constraints on development, the issue is expected to grow further in prominence.

The commercial stakes are potentially high: reduced energy yield affects revenue forecasts, contract-for-difference (CfD) bids, and investor confidence. Wind farm developers are increasingly concerned about the impacts of wake effects, particularly in crowded seabed areas. As turbine arrays grow in scale, the impact of wake interactions is emerging as a material commercial consideration.

In recent years, the wake loss issue has also become a planning consideration – and the policy in this area, relevant to ‘nationally significant’ offshore wind projects, is set to evolve further over the weeks and months ahead.

The position under current planning policy

‘Nationally significant’ infrastructure projects (NSIPs) are subject to a separate consenting process from other planning projects. The Secretary of State must issue a development consent order (DCO) to enable such projects to go ahead. National policy statements have been developed to inform NSIP applications and consenting decisions. For ‘nationally significant’ offshore wind projects in England or Wales, the relevant document is the national policy statement for renewable energy infrastructure (EN-3).

EN-3 does not currently refer explicitly to wake effects, but it does state that impacts on existing offshore infrastructure should be assessed. The UK government has interpreted this in the context of wake effects, requiring developers behind offshore wind NSIP applications to undertake wake effects assessments since 2023. The Awel y Mor DCO set the original precedent in this regard, in which the developer was required undertake “an assessment of any wake effects and subsequent design provisions to mitigate any such identified effects as far as possible” prior to turbine construction.

There’s no established legal right to 'wind flow’ in the UK, and wake loss has not yet been tested in the courts, but the planning system is now treating it as a real and material issue. That shift is significant. It means developers need to think about wake effects not just as a technical or commercial matter, but as something that shapes a consent application.

Historically, wake disputes may have been resolved solely through commercial negotiation outside of the planning system, or by design changes. Several offshore wind developers have publicly been raising concerns about wake effects, and with sites becoming more tightly packed, the pressure to formalise how wake loss is assessed and mitigated is growing,

A more recent offshore wind DCO affirms that the interpretation of NPS EN-3 applied in the Awel y Mor DCO stands. In the recent case, the Secretary of State found that wake effects should be assessed and imposed a requirement on the developer to submit a wake effects plan which “must include details of reasonable steps that have been taken by the undertaker to minimise wake effects” on the existing wind farms.

The departure from previous practice is clear, and the current position is that if there is evidence of a risk of interference with neighbouring offshore wind farms, developers must give due consideration to the extent of those impacts on other offshore windfarms, even if the neighbouring project is at significant distance.

The wider public policy question

Although the imposition of wake effects assessment requirements may inform the extent to which projects may impact not just each other, but the deployment of renewable energy, it is worth asking whether wake loss – which is fundamentally a commercial impact – should be treated as a planning matter at all. Planning is meant to balance public interest, environmental protection and strategic infrastructure delivery. If commercial competition between developers is treated as a planning constraint, it could be argued that the balance is distorted, and there is a risk of overreach if planning becomes a proxy for commercial arbitration.

However, emerging research shows that spatial compression increases the likelihood of wake interactions, and there are question marks over how to best balance competing interests. Including wake effects-related requirements in DCOs is considerably more logical when considering the government’s ambitions to achieve challenging targets for much needed renewable energy: by imposing requirements for assessment, the government is ensuring the extent of wake effects from a neighbouring wind farm is assessed and that it can be considered how much renewable energy is ‘lost’ from the operational tail-end of those existing/built projects.

The concern is particularly acute as the UK targets 43-50 GW of offshore wind capacity by 2030, requiring projects to be sited closer together. Proper consideration needs to be given to how to optimise national energy yield while preserving viability across individual projects. The UK government is aware of the issue. It has tasked the University of Manchester with leading a 12-month study, supported by sector experts and offshore wind farm developers, to build an evidence base on wake effects, their financial implications, and mitigation strategies.

The government needs to take care with how it applies the learnings from this research project, however. If the consenting regime becomes too uncertain or burdensome because of wake-related disputes, it could inadvertently discourage developers from bringing forward projects.

On the other hand, the impacts to existing offshore wind farms need to be carefully considered too, as to impact their operational output of renewable energy is to impact the progress toward renewable energy goals. Although the government-led study may prove helpful in contextualising the issue, and providing an improved evidence base, it is important that solutions pursued do not inadvertently create more uncertainty and obstacles for renewable projects whether already existing, or future ones. That would be counterproductive to the UK’s net zero and energy security goals.

The immediate change of policy on the horizon

While developers and policymakers alike await the outcomes of the University of Manchester-led research, the industry can expect a more immediate change in planning policy around wake effects.

While the EN-3 was the subject of extensive revision under the previous UK government, the Labour government is intent on further updating the document, to support its policy ambitions. The latest revised draft (148-page / 1.08MB PDF), which is subject to parliamentary approval, was presented on 13 November.

Under what is proposed in this latest draft, offshore wind farm developers would be required to make reasonable endeavours to mitigate wake effects on other wind farms, and to work collaboratively.

This represents an evolution of government expectations. In May, a first draft of the revised EN-3 was laid before parliament under which developers would not be expected to eliminate wake effects entirely but rather demonstrate that inter-array wake effects between their proposed development and nearby offshore wind farms had been assessed. In effect, this put into writing the position favoured in recent wind farm decisions.

However, that first draft revised EN-3 also provided that design consideration should be given to how wake loss may affect other projects whether “planned, consented, or operational” – not only those which already exist. In addition to assessment requirements, the government proposed at the time that developers also be required to take “all reasonable steps to minimise as far as possible the impact of wake effects”.

It was not clear what ‘reasonably minimising impacts of wake effects’ would have required. Although the draft suggested that developers demonstrate compliance by evidencing that the project has been configured to ‘reduce impacts’, short of not developing their wind farm in the first place, it was not clear what would satisfy the test of taking ‘all reasonable steps to minimise’ effects.

The revised draft of the new EN-3 contains updates of some important paragraphs. Under what is proposed in that document, developers would have to make “reasonable endeavours to mitigate the impact of wake effects on other offshore wind generating stations”.

The position as it stands under the updated draft is that any residual wake effects – if they remain after any reasonable endeavours to mitigate them and provided that the applicant has made reasonable efforts to work “collaboratively with its neighbours” – would not carry more than limited weight against the project in the consent decision. There is no expectation of inter-project compensation under the planning system where wake effects are present. Further supplementary guidance notes that “the planning system will not adjudicate on matters of compensation for wake loss”. However, the updated draft EN-3 does recognise that such arrangements could be sought outside of the planning process, keeping the option of inter-project compensation on the table.

With the changes it has made to the document, the government has moved the planning system away from being used as a proxy for commercial arbitration to some extent. However, that there is not an expectation of final compensation does not prevent wind farms objecting to their ‘to-be neighbours’ schemes.

The first clues as to how this revised policy might be applied if it were implemented as currently drafted have emerged via a recent offshore wind DCO that has been granted.

That DCO decision includes a wake effects requirement, and a finding that the effects of that project on existing wind farms should be afforded “moderate negative weight in the planning balance”. Building on the precedent that has been established, it requires the developer to provide details of what reasonable steps it has taken to minimise effects but adds “without materially reducing the capacity” of the forthcoming project. There is also a further requirement on the developer to share details of the consultation, and agreement or disagreement, it has had on wake effects with owners of existing offshore wind farms. However, none of the above is required if “alternative mitigation” has been agreed with the owners of existing offshore wind farms.

This DCO decision may reduce speculation on how the proposed revised EN-3 may be applied if approved. The decision encourages holistic consideration of the wake effects issue in light of the various stakeholders’ interests and renewable energy goals. Although ‘alternative mitigation’ is not defined, it is clear this can capture inter-project compensation. Having this option is positive, as it cements that developers can resolve the wake effects issue without the Secretary of State’s intervention whilst retaining the possibility for the issue to be factored into consenting decisions in the event of disagreement.

The prospect of further guidance and other planning policy changes

Three offshore wind DCO applications where wake effects have been raised as an issue during examination await determination between now and March 2026.I It will be interesting to see how the Secretary of State balances this issue in light of the most recent developments.

That the government has commissioned extensive research recognises the complexity of the issue, and the fact that the research programme is in collaboration with strategic bodies such as The Crown Estate and ORE Catapult suggests that wake loss may be a technical consideration for any future leasing rounds and spatial planning decisions.

Spatial planning by the government may have a role to play going forward to reduce the impact of wake effects. However, once an agreement for lease in the seabed is granted, it is fundamentally a commercial issue, as developers must decide how to best utilise their areas to maximise generation capacity and revenue. The government-backed study will also be helpful, creating an evidence base to inform solutions, but caution needs to be exercised against leveraging its findings for further policy changes.

The updated draft EN-3 avoids adding more hurdles to, and asks of, the planning process, in the form of assessments and strict design considerations, which could dissuade investment in the offshore wind sector, and which could counteract the government’s renewables ambitions. From a planning perspective, the government has clarified the position on wake effects – its proposed approach balances the fact that identifying that wake effects is a consideration for progressing renewable energy with the need for early engagement and cooperation between developers.

Whether the issue regarding wake effects is now progressing towards a resolution remains to be seen, with the proof lying in the outcome of upcoming DCO decisions, and whether the developer stakeholders – of both existing and future wind farms – consider their interests sufficiently accounted for.

The updated draft EN-3 will be formally designated once approved by resolution by parliament, or by deemed consent following a 21 sitting-day period, which ends 15 December.

Co-written by Amos Dahl and Alex Tresadern of Pinsent Masons.