Primary vs grey: A critical evaluation of literature sources used to assess the impacts of offshore wind farms

The evidence-base for environmental and social impacts of offshore wind farms (OWF) is increasing with the exponential global growth of the offshore energy sector. In the UK, planning and consenting processes are lengthy (7+ years) and rely largely on evidence from grey literature sources. To meet 2030 and 2050 renewable energy targets and marine net gain ambition, policy and decision makers require access to the best available data. Translating environmental impacts into ecosystem services (ES) provides a qualitative framework by which to evaluate positive and negative outcomes. We review and synthesise UK grey literature (2012-2022) relating to OWF impacts and compare reported ES outcomes with those from global primary literature (2002-2021). Grey literature portrays a largely negative (71%) view of ES outcomes and fails to represent many positive ES outcomes reported in primary literature. In primary literature, 28% of reported ES outcomes are positive, but in UK grey literature this is just 2%. Evidence gaps are highlighted for both literature types, with major gaps for decommissioning outcomes, and sparse evidence for Provisioning ES (8%), Regulating ES (7%) and specific operational pressures. We recommend evidence from both literature types is used to achieve environmentally sound decision making and expedite planning and consenting times.