Offshore renewables

Writing team: Ewa Malgorzata Spiesz (coordinating author), Rayenda Brahmana, Ana Brito e Melo, Andrea Copping, Freya Croft, Isa Olalekan Elegbede, Rafael González-Quirós (co-lead member), Deborah Greaves, Shenghui Li, Eric Mwangi Njoroge, Henrique Paiva de Paula, Jose Rodrigo Rojas, Katherine Viik (lead member) and Rebecca Williams.

Key points

• Ocean-based renewable energy, such as offshore renewable energy (ORE), could deliver around 10% of the global CO₂ emission reductions required by 2050 to sustain a 1.5℃ pathway, and ORE will be a vital tool in meeting the goal of tripling the world's installed renewable energy capacity, as set during the twenty-eighth session of the Conference of the Parties to the United Nations Framework Convention on Climate Change.
• ORE development has high potential for boosting employment and providing local economic benefits. Social equity should be prioritized to ensure that the expansion of ORE does not disproportionately affect already marginalized communities or perpetuate existing inequities.
• Effective policy strategies such as technology push instruments (e.g. research and development grants), market pull instruments (e.g. feed-in tariffs and contracts for difference) and marine spatial planning are necessary to advance the ORE sector and increase the roll-out of ORE technologies.
• Understanding the potential cumulative environmental effects of offshore renewables and implementing effective mitigation measures can reduce harm to marine environments and potentially lead to net positive gains for habitats and ecosystem processes.
• The development of offshore renewables can be part of the solution to the climate crisis if a sense of responsibility is maintained, best practices are followed in measuring potential environmental and socioeconomic effects by using standardized sustainability assessments, unacceptable changes are mitigated and plans are made to reverse course if irreparable damage is found to be being done.

1. Introduction

Developing ORE globally will be pivotal to the energy transition and the decarbonization of the economy Ref 56 Ref 107. Not only can ORE play a role in mitigating global warming and reducing emissions by providing a clean and reliable source of energy, but it also provides opportunities for coastal economic revitalization through enhanced innovation, job creation and the provision of renewable energy to remote coastal locations, such as islands, for a just transition. It offers a clean growth pathway, transitioning the workforce and industries to meeting future development needs, while providing a sustainable means of meeting the growing energy demand.

Offshore wind energy will soon be generated on a large scale at sea, at which point it will be used to supplant conventional energy sources on national grids. Other more emerging marine energy technologies (wave energy, tidal current energy, ocean thermal energy conversion, salinity gradient energy and offshore floating solar) can complement the large-scale generation of electricity using offshore wind by filling gaps to ensure the secure, continuous and equitable provision of energy in off-grid applications. A key off- grid ORE application is electrifying islands and remote coastal communities, which currently generate electricity mainly from fossil fuels. Offshore renewables can provide stability and resiliency as wind and solar energy and energy storage are incorporated into sustainable microgrids Ref 77. Similarly, certain marine energy sources can generate power to be used at sea, replacing battery power on ocean observation and navigation platforms, replacing fossil fuels as aquaculture facilities move further offshore and eventually replacing coastal and transoceanic shipping fuels Ref 77. These emerging ORE solutions can be used to meet the growing need for electricity to power offshore data and computing centres, which are needed to support artificial intelligence.

The present subchapter provides an overview of ORE technologies, including their development status, opportunities, challenges and environmental and socioeconomic considerations, followed by an outline of an ideal pathway for ORE development up until 2050, wherein success will hinge on the ability to address the identified knowledge gaps.

2. Offshore renewable energy technologies that are emerging and available on the market

Development status

The present part of the subchapter contains an introduction to the different ORE technologies, including offshore wind energy, wave energy, tidal energy, offshore floating solar, salinity gradient energy and ocean thermal energy conversion, with a short description of each technology's working principles, resource potential and status. It is important to note that ORE technologies can also be referred to as marine renewable energy technologies (as in the second World Ocean Assessment Ref 29) or ocean energy technologies (Ocean Energy Europe, 2024). According to a report commissioned by the High-level Panel for a Sustainable Ocean Economy, ORE could deliver around 10% of the global CO₂ emissions reductions required by 2050 to sustain a 1.5℃ pathway Ref 65. Use of ORE depends on the efficiency, maturity and cost-effectiveness of the technologies. The working principles and stages of development of various ORE technologies are listed in table 1.

Table 1 Development status of various offshore renewable energy technologies

Source: Prepared by the writing team.

Note: Technology readiness level ranges from 1, which is an innovative idea, to 9, which is a solution ready for market.

Opportunities and challenges

Opportunities and challenges related to the development of ORE are set out in table 2. In the first instance, ORE is likely to need price support until supply chain investments are made and industry learning is consolidated (see part 3 below). Governments can play a valuable role in reducing market risks, thereby reducing financing costs and ensuring lower fuel bills for consumers. To encourage market readiness, Governments might consider appropriate policies, stakeholders, grid connections and financing Ref 93 Ref 26, and some good examples of regulatory frameworks to address such bottlenecks already exist. However, some countries are still at an early planning stage, meaning that the supply chain and operational readiness to deploy are limited. Developing economies may face additional financing barriers, and some may have particular market structures that hinder the penetration of ORE into the energy mix Ref 26 Ref 38. In all markets, the concept of risk-sharing, usually between the Government and the private sector, is integral to market stimulation as bidding in auctions and tenders requires a project developer to carry a large amount of the financial uncertainty and risk Ref 87 given that project approval can be very lengthy.

Table 2 Opportunities and challenges of various ORE technologies

Source: Prepared by the writing team.

Prospective development, including regional potential

Global installed capacity of offshore wind was 75.2 GW in 2023, (Global Wind Energy Council, 2024) which is more than double what it was at the time of writing of the second World Ocean Assessment Ref 29. The International Renewable Energy Agency (IRENA) and International Energy Agency project that at least 380 GW offshore wind will be needed by 2030, and over 2,000 GW by 2050, to keep the world on track for 1.5℃. In 2023, 11 GW offshore wind was connected to the grid, which is a 24% year-on-year increase, the second highest yet (see figure I).

Figure I New and total offshore wind installations worldwide in 2024

Membership of the Global Offshore Wind Alliance, a diplomatic, multi-stakeholder initiative founded by the Global Wind and Energy Council, IRENA and the Government of Denmark, has grown to include over 20 Governments. These Governments have pledged to collaborate on installing 380 GW offshore wind by 2030 and 2,000 GW by 2050 (Global Offshore Wind Alliance, 2024).

There is still an implementation gap between declared targets and the rate of annual installations. Permitting, finance, supply chain and grids are areas that remain key enablers to achieve growth targets and to propel offshore wind power development into a new phase of even faster growth. The World Bank Group found that blended and concessional finance would be important in enabling emerging markets and developing economies to gain access to financing for offshore wind. A report published in 2024 in the United Kingdom of Great Britain and Northern Ireland found that the offshore wind workforce needs to grow sixfold, offshore wind capacity needs to increase sevenfold and current capacity and project build- out rates need to be four times faster if the goals set are to be reached by 2050 (Supergen ORE Hub, 2024).

The planned uptake of tidal stream energy in Europe has increased since 2023, with the United Kingdom and France contracting 70 MW of tidal stream capacity through revenue support systems. This is expected to lead to a global capacity of well beyond 127 MW by2030 (Ocean Energy Europe, 2024).

A total of 13.3 MW of wave energy has been installed in Europe since 2010, of which 1 MW is currently deployed. The other installations have been decommissioned following the completion of testing and demonstration programmes (Ocean Energy Europe, 2024). The rate of deployment of wave energy devices had slowed but is growing again towards levels recorded before the coronavirus disease (COVID- 19) pandemic. Beyond Europe, the United States of America and China have announced development targets and voiced support for ORE (Ocean Energy Europe, 2024).

Project development, including supply chain and grid connection challenges

To unlock the full potential of ORE and achieve ambitious targets, a robust supply chain for installation components, installation and maintenance vessels, and the development of harbours for installation purposes are critical. In Europe, America and Asia, several countries have set ambitious targets - some by 2030 - for offshore developments, necessitating rapid harbour development and an increase in the qualified workforce. In Oceania, the Government of Australia has identified six regions for offshore wind development, which will require new or expanded onshore ports and grid infrastructure to support the industry.

Current renewable energy production and decarbonization targets are driving a rapid expansion of offshore renewables worldwide, which will help to mitigate climate change. Many of the ORE components require "critical materials", including cobalt, copper, graphite, iridium, lithium, manganese, nickel, platinum and selected rare earth elements. Since sources of these materials are often very localized, their supply involves structural vulnerability to supply chain disruptions. Various attempts at the diversification of sources of critical materials have been proposed, such as the Critical Raw Materials Act by the European Commission (European Commission, 2024). Special attention is needed for the supply of copper as demand is rising across multiple sectors, including ORE, other renewable energy technologies, and specific types of car batteries. Copper could soon become a major bottleneck, due not only to limited geological availability, but also to rapid acceleration in demand.

Deep-sea mining could become an option for more equitable access to critical materials, but does carry a set of potential uncertainties and environmental risks, including disruptions to ocean carbon sequestration processes, which could amplify climate change Ref 106. A more sustainable and strategic approach is "urban mining", which is using recycled copper from electronic waste. Urban mines potential is nearly equivalent to land-based reserves. Given that copper is highly recyclable, fostering circular economy strategies is essential.

Another method of critical materials extraction that is currently in an advanced stage of research and development is from seawater containing critical minerals at low concentrations. Extraction requires the use of large volumes of seawater; the process is being examined in conjunction with emerging ORE technologies such as ocean thermal energy conversion Ref 98. The environmental impact of this new method is to be determined but can likely cause less impact compared to deep-sea mining.

The lack of a stable supply chain for critical materials used for renewable energy devices and the lengthy process of developing new sources (e.g. exploration and mining infrastructure development) may result in critical materials becoming another bottleneck in ORE large-scale roll-out. On the positive side, the situation may increase research and development in circular strategies for raw materials used in renewables.

Comprehensive project sustainability assessments are vital for fostering resilient ORE investments and ensuring sustainable energy development. Such assessments should include the risks posed by projects to the sustainability of marine ecosystems. Assessments should consider both positive impacts (handprints) and negative impacts (footprints), as well as impacts on ecosystem services, such as cycle assessments of components used and other aspects of sustainability Ref 45. Key risks (i.e. technology-related, deployment-related, regulatory, financial and reputational) can be effectively managed to protect the environment. These risks and their potential impacts are summarized in table 3.

Table 3 Risks associated with the deployment of offshore energy installations

Source: Prepared by the writing team.

3. Socioeconomic aspects

The increased uptake of ORE is expected to lead to change in some coastal communities, which will bring about social and economic impacts Ref 58. The socioeconomic impacts of global ORE development should be evaluated alongside other offshore energy sectors, such as oil and gas, which may have partly comparable impacts (United Nations Environment Programme Finance Initiative, 2022). The social impacts of ORE have not been comprehensively considered and there is a need for further research in this space (European Court of Auditors, 2023). As outlined in table 4, the consideration of socioeconomic impacts requires clarification on distribution, geographical and temporal scope and the nature of the impact Ref 58.

Table 4 Complexities of identifying the socioeconomic impacts of the development of offshore renewable energy infrastructure

Source: Prepared by the writing team.

Social considerations in the continued development of offshore renewables

As outlined in table 5, identifying the social impacts of ORE is complex. However, the need to embed equity in the development of ORE and energy transitions more broadly is the crux of all social considerations. It is imperative that the increased uptake of ORE does not reinforce the status quo or exacerbate wealth inequality and existing inequities. Equity therefore needs to be foregrounded in the processes and outcomes of ORE development, which will subsequently help to advance some sustainability goals (Villavicencio Calzadilla and Mauger, 2017). While the development of ORE has been linked to the advancement of the Sustainable Development Goals, the relationship between these two phenomena is often complex and the development of ORE-related infrastructure can both enable and inhibit the advancement of the Goals Ref 105. Processes such as planning, procurement and investment are significant in ensuring the sustainable development of the ORE industry (Bourg- Meyer, 2022).

The social aspect of ORE could involve creating jobs for members of underrepresented groups, including women, ethnic minorities, Indigenous Peoples, sexual minorities, persons with reduced mobility and young persons. Although the energy transition is under way in many countries, there is still a gap in job creation for underrepresented groups, according to the International Labour Organization (ILO). Furthermore, initiatives such as the Offshore Wind Sector Deal, published in the United Kingdom in 2019, can play a crucial role in fostering inclusive representation in the ORE sector. The deal was an industry commitment that set targets to increase diversity by raising the representation of women in the offshore wind workforce from 16% in 2018 to at least 33% - with an ambition to reach 40% - by 2030.

Beyond voluntary commitments, legal frameworks in several countries also support inclusivity in offshore wind development. In the United States, impact assessments for offshore wind projects under the National Environmental Policy Act evaluate the social impacts of offshore wind projects. Similarly, in Canada, the Impact Assessment Act requires assessments of ORE projects to consider gender minorities and other underrepresented groups, promoting fair participation in the sector. In the United Kingdom, the Equality Act (2010) provides a legal foundation for advancing diversity and inclusion across industries, reinforcing efforts like the Offshore Wind Sector Deal.

In order to put the rights of Indigenous Peoples at the forefront of energy transitions, including in the development of ORE, the principles of free, prior, and informed consent, as set forth in the United Nations Declaration on the Rights of Indigenous Peoples, should be upheld (Organisation for Economic Co-operation and Development (OECD), 2024; United Nations, 2007). Furthermore, mechanisms should be enabled to support Indigenous, traditional owner and local community knowledge and Indigenous-led research and governance and to enhance the importance of Indigenous knowledge systems Ref 50. At the same time, increasing Indigenous representation requires recognizing the systemic barriers to participation and leadership for Indigenous Peoples Ref 50.

Decisions relating to the use of ocean space should acknowledge the plurality of human relationships with the ocean Ref 22. Social acceptance can influence the success of the development of ORE projects (European Court of Auditors, 2023). Research shows that often there is a disconnect between the broad support for the development of offshore renewables among the general public and local resistance in adjacent communities Ref 49. Place-based understanding and approaches will therefore be essential in the continued development of ORE.

Conflict arising in relation to the use of marine space, including spatial exclusion of fishers, can be mitigated by marine spatial planning Ref 54. Conflict should not be seen as necessarily negative, as it is often through conflict that better social and environmental outcomes can be achieved. However, it is important that appropriate mechanisms for navigating this conflict be developed Ref 76 Ref 103 Ref 94.

Economic considerations

ORE development, including wind power, tidal power, wave power and other technologies, creates demand for a wide range of components and services, leading to new jobs and local economic development. ORE development therefore holds significant potential for job creation, provided that training programmes expand and workforce initiatives adapt to evolving demands. The High-level Panel for a Sustainable Ocean Economy found that offshore wind has a higher capacity for jobs than the fossil fuel industry and in general has a better gender balance Ref 78. The International Renewable Energy Agency (IRENA) estimated that a 500-MW offshore wind project directly creates 2.1 million person-days of work, or about 10,000 person-years of work, over its lifetime. Offshore wind presents an opportunity to revitalize coastal towns, cities and communities, where new investments can regenerate areas that have previously seen economic decline.

The projections of potential employment from ORE for certain countries and regions are shown in table 5. However, significant challenges remain in ensuring job supply for the growth of the ORE sector. As the sector expands, the demand for skilled workers will increase, especially with the ambitious development goals set by multiple nations. Job creation is constrained by factors that include the number of large-scale projects, regulatory complexities, technological advancements, and financing and investments, as well as training and skills development. The ORE sector requires a specialized workforce Ref 97 Ref 100 but, in many regions, there are not enough training programmes to meet the sector's needs, leading to skills gaps in areas such as advanced engineering and operational expertise (Skoudopoulos, 2019; López-Morado and others, 2024). The high costs of training, alongside rapidly evolving technologies, complicate efforts to equip the workforce Ref 100. Investing in robust training frameworks and education initiatives is essential to meet growing employment demands and ensure the long-term sustainability of the sector Ref 24.

Table 5 Projected job creation potential of the offshore wind energy sector

ª According to industry-level projections.

Source: Prepared by the writing team.

Socioeconomic impact assessments

Socioeconomic impacts are assessed as part of the environmental impact assessment process when developers are applying for a licence or consent. The intention is to identify the potential impacts and to explore mitigation and enhancement measures.ⓘ However, impact assessments may not adequately show the risks and opportunities (Scotland Marine Assessment, 2020) nor accurately reflect social and cultural values that are not readily transferable as quantifiable metrics. Both qualitative and quantitative methods will be needed to accurately measure the full scope of socioeconomic impacts Ref 58.

4. Governance of offshore renewables

Strong governance mechanisms and supportive policies are essential to attract the necessary financial investment to support the expansion of ORE while also working towards social and environmental outcomes. Governance is a system of organization and operation that includes components such as decision-making, compliance and accountability. Supportive policies will enable the technology to reach commercial-scale implementation while ensuring that this expansion aligns with sustainable objectives. It is crucial to foster policies that promote long-term consistent deployment trajectories and an accelerated cost reduction rate. In the present part, various policy strategies that have been effectively used as governance mechanisms to encourage the advance of the sector are explored.

Policy based on both "technology push" and "market pull" instruments is effective for the development of OREs. Those instruments are essential for guiding technology through the various stages of the innovation chain, effectively supporting its development from the conceptual stage to initial adoption and widespread use. Some policy measures are aimed predominantly at advancing technologies in their early stages, while others play a crucial role in later stages, moving towards broad market acceptance.

The International Vision for Ocean Energy, outlined in the road map by the International Energy Agency Technology Collaboration Programme on Ocean Energy Systems, serves as a strong example of how the balance between push and pull policies is critical for advancing ocean energy technologies.

"Technology push instruments" are designed to encourage the research and development of new technological ideas and advance them to the stages of demonstration and initial commercialization. Notable examples include tax credits for research and development, grants, prizes, concessional financing and matched equity funding. Such support is critical in the early stages of technology development and implementation as it makes innovative projects more attractive to private investors. Government funding for research and development is vital for technological innovation in this sector and should include funding for both basic and applied research, as well as support for demonstration projects to prove their feasibility and performance under real sea conditions. It is important that such measures be focused on areas identified as priorities to enhance the performance of devices and reduce costs associated with development, implementation, maintenance and decommissioning. Such support mechanisms are particularly suited for promoting international collaboration, which is a key factor in accelerating cost reduction. Multilateral development banks, such as the World Bank and the Asian Development Bank, can play a significant role in promoting new technologies because they offer funding and risk mitigation that can attract additional private sector investment, which is particularly important for large-scale demonstration projects.

A strong illustration of technology push in action is seen in projects funded under the European Green Deal and Horizon Europe. These initiatives include multi-source offshore energy parks (European Scalable Offshore Renewable Energy Sources (EU-SCORES), 2024), tidal array energy parksⓘ and wave energy parks supported by the European Union Innovation Fund Ref 19. The Europe Wave programme, supported by the Basque Country and Scotland along with the European Commission, represents another example of coordinated efforts to drive innovation in ocean energy technologies.

"Market pull" instruments are essential for developing a commercial marine energy sector. The two most relevant financial instruments used to encourage the development of marine renewable energies have been feed-in tariffs and contracts for difference, which have each been implemented in various countries. Feed-in tariffs offer long-term contracts to energy producers, guaranteeing them a fixed price for the electricity generated, which helps to mitigate the financial risk associated with the high initial costs of marine renewable energy projects. Similarly, contracts for difference stabilize revenues for energy producers by ensuring that they receive a fixed price for the energy produced, regardless of market fluctuations. An illustrative case is the United Kingdom, where contracts for difference are the Government's main mechanism for supporting low-carbon electricity generation. There have been six auctions, or allocation rounds, to date, which have seen a range of different renewable technologies competing against each other for a contract. They have been successfully implemented to boost the offshore wind energy sector and, more recently, the tidal energy sector.

In the United States, east coast offshore wind projects have been experiencing financial stress. Macroeconomic factors, such as rising costs of materials, supply chain disruptions and increases in the cost of capital due to increased interest rates, have, in combination with regulatory issues, brought about these challenges. Many contracts were agreed prior to the COVID-19 pandemic and certain geopolitical events, and did not include sufficient indexation linkages. Furthermore, issues such as slow permitting and differing supply chain requirements at the state level have increased risk and cost of capital. This experience highlights the need for better financial support mechanisms and risk mitigation strategies, such as indexation of offtake contracts, but also the need for clear governance and regulation that harmonizes requirements between state and federal regimes and recognizes the importance of efficient permitting procedures.

Another crucial aspect of governance for the development of marine renewable energy is the setting of clear and ambitious targets, accompanied by a clear and specific plan to deliver on those targets, with yearly milestones. Such targets demonstrate the Government's commitment to encourage investment and foster technological innovation in renewable energy (examples of offshore wind in Europe are set out in table 6). This is particularly important in the ORE sector, where the long-term financial viability of projects is critical for investors. In addition, these targets allow policymakers to align regulations, subsidies and support mechanisms with a common objective. Most importantly, targets and associated road maps and plans give confidence to investors and manufacturers to invest in facilities and projects. Targets act as catalysts for an energy transformation. For example, the European Union has set a target of 300 GW of offshore wind capacity by 2050, a significant increase from the approximate 12 GW in recent years. This ambitious goal is part of a broader strategy to achieve carbon neutrality and strengthen the energy independence of the bloc. The Kingdom of the Netherlands has set an ambitious target of achieving 3 GW of offshore floating solar capacity by 2030, showcasing its commitment to diversifying and expanding its renewable energy portfolio.

Table 6 Offshore wind energy capacity targets (GW)

Source: Prepared by the writing team.

Note: ª including 5 GW floating offshore wind; b in operation or under development by 2027 (Global Wind Energy Council, 2024).

A well-designed regulatory framework is especially essential for the development of emerging offshore renewables. As the sector progresses globally, concerns about the potential effects of such devices on marine animals, habitats and the broader environment remain a significant challenge. To address those concerns effectively, a regulatory framework that provides clarity and predictability for developers is needed. Such a framework would outline the requirements and procedures necessary for the implementation of projects at sea to ensure that projects are both feasible and sustainable. To encourage growth in the sector, it is important that regulatory frameworks include effective licensing processes that minimize bureaucratic barriers, thereby speeding up the deployment of new technologies and ensuring that project timelines are manageable, while not compromising on social and environmental standards. Equally important is the need for efficient environmental impact assessments. As understanding of the potential environmental effects of ORE projects grows, environmental impact assessments should be streamlined to focus on assessing risks that are significant and warrant careful study. In addition, the regulatory framework should incorporate mechanisms to retire environmental risks (i.e. recognizing and managing risks once sufficient data is gathered), thereby enabling the industry to move forward confidently while maintaining high environmental standards. Notably, adaptive management strategies, which allow for adjustments based on real-time environmental monitoring, have been promoted in various countries.

Another important aspect of governance is marine spatial planning, which allows for the strategic allocation of marine spaces and ensures that OREs can coexist with other maritime activities, such as navigation, fishing and tourism. Marine spatial planning helps to manage the spatial and temporal distribution of human activities in marine environments, optimizing resource use while minimizing conflicts and environmental impacts. An innovative application of marine spatial planning is the adoption of multi-use strategies, which involve the co-location of different activities in the same marine area. By gathering data and knowledge for the planning area and engaging with affected stakeholders, marine spatial planning processes can support co-location of different activities in the same area.

As an example, China is now conducting three-dimensional development of ocean space to encourage more efficient and intensive utilization of marine resources. This approach involves the division of marine areas into vertical layers (e.g. the surface, water body, seabed and subsoil) to determine the use of the marine area on the basis of actual conditions, as well as co-location of offshore floating solar photovoltaics and aquaculture, offshore wind farms and marine ranching, and offshore wind farms and tourism. The European Union's maritime spatial planning directive exemplifies how marine spatial planning can be effectively implemented: the directive requires European Union member States to develop maritime spatial plans that balance economic, social and environmental objectives, including the integration of ORE with other marine uses, thereby supporting the European Union's goals for sustainable growth of maritime economies and the responsible use of marine resources. The directive emphasizes a collaborative approach, involving stakeholders at all levels in the planning process to ensure that the plans reflect a broad range of interests and insights. Similarly, the "area passports" concept in the Kingdom of the Netherlands represents an innovative approach to enabling the coexistence of multiple offshore activities, such as energy production, aquaculture and other uses of the North Sea. Area passports help stakeholders to understand which activities can be integrated into a particular area, promoting multi-use strategies that optimize the use of marine resources while minimizing conflicts.

5. Environmental impacts

Understanding the risks that ORE production pose to marine animals, habitats and ecosystem processes requires specificity that links each part of an offshore device or system to species, habitats and processes. Using a stressor-receptor framework allows the attributes of each stressor (portion of device or operation that can cause stress, injury or death) to be linked to the specific receptor (animals, populations, habitats, oceanographic and ecosystem processes) of concern Ref 62. The key stressors and receptors of concern for offshore renewable technologies are listed in table 2. Eight major stressors have been recognized by the marine energy and offshore wind communities Ref 56 Ref 83:

• Collision risk: animals colliding with moving turbine blades (under water for tidal and ocean current turbines, in the air for wind turbines)
• Underwater noise: natural sounds under water being masked by noise from marine energy and offshore wind energy
• Electromagnetic fields: emissions from power export cables and underwater substations
• Changes in habitats on the seafloor and in the water column
• Changes in oceanographic conditions due to the presence and operation of devices
• Entanglement with multiple mooring lines securing systems
• Displacement: presence of many devices affecting animal migration and movements
• Chemical releases: onboard chemicals (for offshore wind, ocean thermal energy conversion and salinity gradient energy) released into the ocean

Levels of confidence for some of the stressor-receptor interactions are still being established, while the results for some technologies, such as offshore floating solar, are inconclusive and require further research. However, the general environmental risks and impacts related to the deployment of infrastructure offshore are similar to those related to offshore non-renewables described in subchapter 3B.

Table 7 Offshore technology stressors, receptors and potential mitigation strategies

Source: Prepared by the writing team.

Abbreviation: n/a, not applicable.

6. Impact mitigation strategies

Amid deep concerns about the potential negative impacts of ORE installations, there is growing discussion about strategies for mitigating such impacts in order to achieve a biodiversity-compatible energy transition Ref 47 Ref 81 Ref 20. There is also growing interest in the potential positive impacts of ORE deployments on marine ecosystems, such as offshore wind turbines fostering localized increases in marine biodiversity and small-scale fisheries limiting industrial-scale fishing activities. Even though uncertainties exist due to insufficient evidence Ref 23, the present part of the subchapter outlines the existing mitigation strategies for marine renewable energies through specific risk scales, project timescales and spatial scales.

Understanding the effects of ORE on ecosystems is crucial for sustainable oceans Ref 33. However, many knowledge gaps, especially concerning the cumulative impacts of ORE over long distances and long periods, still need to be addressed, as regulations generally focus on one species or habitat at a time Ref 36. Reconciling renewable energy production with environmental protection using a precautionary approach requires a balanced strategy that integrates careful planning, robust regulations and adaptive management, and will involve finding compromises among and balancing the interests of different stakeholders. Such a strategy might include both spatial and technical solutions, as well as considerations related to the licensing of marine renewable projects and general compensation measures.

Mitigating the risks of offshore renewable energy (ORE) technologies is associated with the stage in the project life cycle that considers the duration and extent of the pressure exerted by the devices and the scale of the project (timescale of risk mitigation). It can include actions "before the fact" (i.e. avoiding impact), including design, deployment methods, operational strategies, maintenance methods and decommissioning actions (see table 8).

Table 8 Environmental impact mitigation strategies hierarchy throughout the ORE life cycle

Source: Prepared by the writing team.

The impact mitigation hierarchy provides developers with a logical framework to address the potential negative impacts of development on biodiversity and ecosystem services. It is applicable to projects in any sector, including ORE, and is based on the sequential and iterative application of four actions: avoid, minimize, restore and offset. Several existing mitigation measures can be applied across all phases of an ORE project. The environmental impact mitigation strategies hierarchy, which considers optimal environmental impact minimization throughout the life cycle of ORE, is fundamental to best practice environmental management Ref 48. Multiple decisions in the process of concession, installation and operation of ORE can help to avoid environmental impacts through sensible adaptive operations. Adaptive operations include site selection to avoid important seabird feeding areas, construction timing to minimize effects on spawning fish, and the routing of construction and maintenance vessels to minimize wildlife disturbances. Systematic environmental impact monitoring can provide the data necessary to devise and improve such adaptive operation strategies (see part 5). One measure that helps to reduce the environmental impact of offshore wind farms is a vision-based mitigation strategy of painting one of the wind turbine blades black or using achromatic patterns on the blades. A study conducted onshore on Smøla in Norway has shown that such a mitigation strategy could reduce the annual bird fatality by 70% Ref 84.

Other solutions under the impact mitigation hierarchy are aimed at restoring biodiversity. One example is artificial reefs, which are structures designed to mimic the natural characteristics of reefs or other marine habitats Ref 110. They can be strategically placed on the seabed as scour protection for energy infrastructure or in the vicinity of energy infrastructure to enhance biodiversity and restore food web complexity Ref 86. The structures serve as substrates for the attachment of various marine species and provide shelter and foraging opportunities for fish, crustaceans and other aquatic organisms. By fostering the establishment of diverse marine life communities, artificial reefs contribute to the overall health and resilience of offshore ecosystems. Lastly, impact mitigation measures can include efforts to offset environmental impacts and enhance biodiversity. Ecological compensation may also be "out-of-kind", meaning that it is provided in a different location from where the impact is made. One example could be the reoxygenation of seawater using oxygen that is a by-product of offshore green hydrogen production, but the technology is yet to be validated in offshore conditions.

All of the above-mentioned measures can be called nature-inclusive design or biodiversity-positive design as they go beyond mitigating the impacts of the development and create a net positive impact. The increasing incorporation of such measures into offshore installations is becoming necessary for the successful application of offshore project developers to build wind and/or multi-source offshore energy parks, in line with non-price criteria in offshore wind tenders (for example, in the Kingdom of the Netherlands and the United Kingdom).

To ensure sustainable ORE development, mitigation strategies should be applied at multiple spatial scales in alignment with global, regional and local governance frameworks. Such strategies should integrate ecological and social considerations, particularly net marine gain, which is the net positive effect on marine biodiversity and ecosystems resulting from development projects.

International policies and frameworks provide a foundation for sustainable offshore energy development. Global instruments, such as the United Nations Convention on the Law of the Sea, which sets out the legal framework within which all activities within oceans and seas must be carried out, and initiatives such as the Sustainable Development Goals offer high-level guidance on biodiversity protection and climate action.

The transboundary impacts of ORE projects necessitate coordinated regional strategies to mitigate cumulative and shared effects. Regional environmental agreements, such as the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention), and cross-border cooperation can ensure that environmental standards are upheld across multiple jurisdictions. Environmental and social impact assessments and environmental impact assessments have been used for mitigating local impacts, applying a conservative approach to uncertainty and managing the cumulative effects of multiple projects in a single region to balance renewable energy generation with environmental protection Ref 48.

At the national and local levels, strategies should be tailored to mitigate the direct impacts of offshore wind projects. Such strategies should cover local innovative and sustainable pathways, including localized environmental impact assessments, marine spatial planning, and the creation of marine protected areas (MPAs) to strategically manage the location of offshore energy infrastructure, minimizing impacts on critical marine habitats and species Ref 72.

7. Pathways to achieving sustainability: a vision for offshore renewable energy in 2030, 2040 and 2050

The present part of the subchapter provides a positive vision of future developments in the ORE sector. As the vision is based on predictions rather than evidence, the statements can be considered inconclusive.

By 2030 global and local decision makers will understand that a healthy ocean is the basis of a sustainable blue economy, and that they must move beyond a business-as-usual approach, simultaneously targeting economic development, ecological sustainability and human well-being. The ocean and the wind near the ocean's surface will be sustainable energy sources and could unlock new opportunities in the fight against climate change. Offshore energy development will be widespread, tools such as marine spatial planning and adaptive management (learning by doing) will be applied, offshore space will be used for multiple purposes and standardized quantitative assessments of the sustainability of the blue economy will be routine. Efforts to understand the interactions of offshore infrastructure with nature, design nature- inclusive offshore installations and deploy adaptive operations to ensure no harm will have resulted in environmentally friendly installations that provide net marine biodiversity gain. Such efforts will also have allowed for the sustainable growth of ORE, avoiding and minimizing environmental impacts on the oceans.

By 2040, robust and sustainable business models and financing structures will have been developed that support economically sustainable commercial arrays of multiple types of offshore energy production, including offshore wind, wave and tidal, ocean thermal energy conversion, salinity gradient energy and floating solar. The design of global technology facilitation mechanisms will enable knowledge-sharing and access to science, technology and innovation in ORE technologies, helping to close the equity gap in access and enabling the roll-out of economically and environmentally sustainable technologies in developing countries.

By 2040, comprehensive quantitative socioenvironmental impact assessment tools will be widely applied by decision makers. This will result in fair assessments of the impacts - both local and global, both adverse and beneficial - of offshore energy on the oceans, as well as solutions that ensure energy justice and equity. The tools will be accessible, enabling the development of a sustainable blue economy on all continents while preserving the health of the ocean. New offshore installations worldwide will be focused on nature preservation and nature-inclusive design to protect and restore ocean biodiversity.

In 2050, the ORE sector, as part of a sustainable blue economy, will encompass multiple sectors and cross-sectoral activities related to the ocean and sustainability, including environmental sustainability, economic growth, social inclusion and equity. Increasing coordination and cooperation among different marine sectors will maximize the sustainable use of the oceans. The further promotion of ORE technologies in developing countries, including through concessional and preferential terms, mutual understanding and fair equity sharing, will result in a large-scale roll-out of sustainable offshore technologies all around the world.

By 2050, the surface of the oceans occupied by ORE will have increased tenfold compared with the time of writing, while yield will have increased fortyfold as technological advancements will have allowed for moving further away from shore. Offshore space will combine multiple sources of ORE (offshore wind, offshore floating solar or wave energy), aquaculture, hydrogen production and critical mineral recovery for the best use of ocean space. Nature-inclusive and environmentally friendly designs will have helped to avoid and minimize environmental impacts and increase biodiversity, thereby mitigating climate change and the biodiversity crisis.

Most Governments will have set renewable energy goals, including the rapid scale-up of ocean energy technologies beyond offshore bottom-fixed wind, such as offshore floating wind, wave, tidal, offshore floating solar and ocean thermal technology conversion, resulting in 4 TW of ocean energy installed worldwide by 2050 and the limitation of global warming to 1.5℃.

8. Summary

Understanding risks related to ORE development can lead to designs, deployment methods, operational modes, maintenance tasks and decommissioning pathways that will minimize disturbances and harm to marine animals, habitats and ecosystem processes. Similarly, effective mitigation measures can be designed to minimize such risks. With the application of nature-based designs and operational modes, sustainable ORE development can support both climate change mitigation and biodiversity protection and improvements.

The increased uptake of ORE is expected to lead to change in coastal communities. Social equity should be prioritized in the consideration of the socioeconomic impacts. The rights of Indigenous Peoples and communities need to be foregrounded in the planned and continued development of ORE. Such development has a high potential for employment and local economic benefits, but investment in training, education and capacity-building is essential to overcome potential challenges. Assessing the impacts on coastal communities will require further research and will need to include both qualitative and quantitative analyses.

Knowledge gaps to be filled to enable the ORE vision, as outlined in part 7, are:

• Lack of research and innovation in new and emerging technologies, including those that will achieve hybrid solutions, grid integration, cost reduction, derisking, a circular economy for ORE components and a whole system approach.
• Lack of access, especially for developing countries, to accurate data or methodologies on resource characterization, environmental risks, application of nature-based social and economic assessments, life cycle assessments and technology assessments, and financial direction, as well as data on seabed conditions and living marine resources.
• Lack of access in many nations to knowledge and best practices for developing and implementing marine governance.
• Lack of qualified personnel in key government departments and agencies to deal with certain aspects of the project development life cycle, such as permitting.
• Lack of financing possibilities for ORE technologies in the least developed countries and limited financing possibilities in some of the emerging markets and developing economies, resulting in slow uptake of ORE technologies. Sustainable Development Goal target 17.6, which is to enhance knowledge-sharing and cooperation on and access to science, technology and innovation through a global technology facilitation mechanism, sets out a pathway for closing the gap in access to ORE technologies.
• Limited promotion of the development, transfer, dissemination and diffusion of ORE technologies to developing countries on favourable terms, including on concessional and preferential terms, as mutually agreed, as set out in Sustainable Development Goal target 17.7.
• Lack of open access to data and information that follows Findable, Accessible, Interoperable and Reusable (FAIR) and FAIR, Artificial Intelligence Readiness and Reproducibility (FARR) principles, so that all decision makers and developers have access to the same high-quality information. Currently, large amounts of environmental data that could be open and readily available are being held as proprietary information.

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