Non-technical summary A substantial increase in wind energy deployment worldwide is required to help achieve international targets for decreasing global carbon emissions and limiting the impacts of climate change. In response to global concerns regarding the environmental effects of wind energy, the International Energy Agency Wind Technical Collaborative Program initiated Task 34 – Working Together to Resolve Environmental Effects of Wind Energy or WREN. As part of WREN, this study performed an international assessment with the global wind energy and environmental community to determine priority environmental issues over the next 5‒10 years and help support collaborative interactions among researchers, developers, regulators, and stakeholders. Technical summary A systematic assessment was performed using feedback from the international community to identify priority environmental issues for land-based and offshore wind energy development. Given the global nature of wind energy development, feedback was of interest from all countries where such development is underway or planned to help meet United Nations Intergovernmental Panel on Climate Change targets. The assessment prioritized environmental issues over the next 5–10 years associated with wind energy development and received a total of 294 responses from 28 countries. For land-based wind, the highest-ranked issues included turbine collision risk for volant species (birds and bats), cumulative effects on species and ecosystems, and indirect effects such as avoidance and displacement. For offshore wind, the highest-ranked issues included cumulative effects, turbine collision risk, underwater noise (e.g. marine mammals and fish), and displacement. Emerging considerations for these priorities include potential application to future technologies (e.g. larger turbines and floating turbines), new stressors and species in frontier regions, and cumulative effects for multiple projects at a regional scale. For both land-based and offshore wind, effectiveness of minimization measures (e.g. detection and deterrence technologies) and costs for monitoring, minimization, and mitigation were identified as overarching challenges. Social media summary Turbine collisions and cumulative effects among the international environmental priorities for wind energy development.

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We estimated the technical potential for the offshore wind (OSW) resource in the United States under two siting regimes to characterize the uncertainty pertaining to the local drivers of siting within a national context. We established Open Access and Limited Access regimes to represent upper and lower bounds on OSW deployment, respectively. These included spatial constraints such as technology depth limits, military use areas, protected areas, existing infrastructure, shipping lanes and more. The same spatial considerations are also considered in the Limited Access regime, but with additional buffers to existing infrastructure as well as a reduced capacity density assumption. Capacity density is the concentration of wind energy development for a given area specified in terms of megawatts (MW) per square kilometer (km 2 ). In the Open-Access regime we used a 5 MW/km 2 assumption, while in the Limited Access scenario we assumed 3 MW/km 2 . This difference reflects our intention for the Open-Access scenario to serve as an upper bound for OSW technical potential, with the Limited-Access scenario as a lower bound. We also applied three technology advancement scenarios to each of the siting regimes. The three technology scenarios (Conservative, Moderate, and Advanced) represent plausible improvements in turbine technology including increased rated power and higher hub heights.

The National Renewable Energy Laboratory staff would like to thank the Igiugig Village Council for helping to arrange logistics and hosting the team, along with other stakeholders and partners from around Alaska and the country during their visit January 23-25, 2019. The assistance of AlexAnna Salmon, Christina Salmon, and Karl Hill was essential to the success of the site visit. Other Igiugig residents, Igiugig Village Council staff, the teachers and students at the school, and many more were actively engaged and contributed to the site visit activities. The U.S. Department of Energy's Water Power Technologies Office provided support for this project. Quyana! v This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

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