What is the upper-bound circularity performance of wind turbine blade recycling? A comparative assessment of mechanical, thermal, and chemical routes under current and optimised conditions

The rapid deployment of wind energy is creating an end-of-life challenge for wind turbine blades (WTBs), whose large size and composite structure constrain recycling and material recovery. Existing studies compare WTB recycling technologies but rarely estimate upper-bound circularity performance under explicit technological, material-quality and substitution conditions. This study evaluates the upper-bound circularity performance of mechanical, thermal and chemical recycling and examines whether approaching these conditions yields environmental and economic benefits. Environmental Footprint-based life cycle assessment is combined with the Product Circularity Indicator (PCI), Total Substitution Potential (TSP) and Economic Value (EV) for a 53-tonne WTB under current, improved and technologically optimised configurations. Mechanical recycling reaches PCI 0.79 and TSP 36 %, shifting from a net climate burden of 14.7 t CO 2 -eq to a net credit of 13.1 t CO 2 -eq, although EV remains negative because of the low value of downcycled outputs. Thermal recycling reaches PCI 0.94 and TSP 31 %, delivers a net climate credit and achieves the highest EV (€31,415) under technologically optimised conditions. Chemical recycling achieves the highest PCI (0.98) and a TSP of 30.6 %, but solvent production dominates its environmental burdens; solvent recirculation reduces climate impacts by 42 % relative to the improved configuration. The results show that higher circularity does not necessarily reduce environmental impacts or improve economic performance and support more realistic recycling targets and technology-development priorities for WTB and composite waste management.