Critical assessment of the scope and applicability of circularity indicators for the sustainable life cycle management of wind turbine blades

The decommissioning of wind turbines is expected to generate large volumes of composite wind turbine blade (WTB) waste that should be handled properly to avoid negative effects on the environment. Despite the growing interest in sustainable life cycle management (LCM) strategies applicable to WTBs, circularity indicators are still rarely used to support decision-making processes. This study addresses this gap by evaluating the scope and practical applicability of circularity indicators across WTB-LCM pathways, stages, and processes. A systematic literature review was conducted covering 158 peer-reviewed papers and identifying 120 circularity indicators, which were subsequently screened using three complementary matrices (extended RACER, circular composite design, and wind sector-specific criteria). This process led to the selection of 13 indicators considered most relevant to the wind industry. Although no single indicator comprehensively captures circularity across all stages and dimensions, the Materials Efficiency Metric was identified as the most suitable for the beginning and middle stages of the life cycle, while the Carbon Footprint Formula was considered most appropriate for the end-of-life stage. Nonetheless, both exhibit relevant limitations for decision-support in practice, as none of the selected indicators fully captures composite-specific quality parameters, such as fibre degradation, resin compatibility, or the potential for reintegration into high-value applications. Building on these findings, the study identifies three main directions for future research: (i) the development of circularity indicators that incorporate underlooked life cycle stages, such as installation, operation and maintenance; (ii) the integration of material quality parameters, such as fibre integrity and resin compatibility, into the design of new indicators; and (iii) the analysis of empirical case studies to determine the maximum circularity performance that could be achieved across the LCM of WTB, in order to support the development of circular innovations. These areas are essential for advancing more comprehensive, system-level assessments and supporting effective strategies for the sustainable energy transition.