A life cycle assessment of retired wind turbine blade management

Caroline V. Cameron

doi:10.17918/00011193

The wind industry is expanding to meet net zero energy emission goals set by the International Energy Agency. Cumulative US wind energy generation exceeded 150 gigawatts in 2023, accounting for 12% of all US electricity generation and 15% of the cumulative global wind capacity. Wind turbine blades (WTBs) are increasing in length to help meet the expanding wind energy demand. This growth has been enabled by maturing material selections. Glass fiber reinforced polymer composites (FRPC) decrease the weight and increase the strength and stiffness of the exterior shell of a blade. However, these composite materials do not readily break down and tend to be landfilled in 7-10 meter segments at their end-of-life (EOL). Blades pack less efficiently in the landfill compared to other waste streams because of their hollow design, which can be mitigated by shredding, though this isn't common practice in the US. In this work, a multi-criteria decision-making framework is developed to compare alternative EOL pathways that may be used to maximize the returned value from the materials in retired blades. This framework suggests that cement co-processing is an active pathway to handle the current stream of retired WTBs. In cement co-processing, waste materials are input to a cement kiln as alternative sources of virgin raw materials and fuels for cement clinker production. However, present and future advancements in material choices for WTBs - especially the increasing use of carbon fibers instead of fiberglass - will make this process unsuitable to manage this material stream in the future. Pyrolysis is a near-term technology that may be more suitable for carbon fiber-reinforced blades and provides a pathway toward recovery and reuse of the glass fibers in the current wind blade waste stream. In pyrolysis, the polymers in the WTB are thermally decomposed and converted into high-energy hydrocarbons and the reinforcing fibers are recovered. The hydrocarbons can be used as an alternative fuel source and the recovered fibers can be reused, remanufactured, or downcycled into other applications. A life cycle assessment (LCA) is performed to compare the environmental impacts of producing cement clinker and fiberglass with conventional raw material feedstocks or a blended feedstock of raw materials and retired blades. Key findings suggest that cement co-processing may provide environmental benefits to the cement industry. However, the added burden to recover glass fibers from the blades using pyrolysis and remanufacture them into new fiberglass increases the environmental burden of fiberglass manufacturing. Monte Carlo simulations are performed to explore the uncertainty in these results based upon variability of input parameters in the literature. This study suggests that the energy demands for high-energy process steps contribute the greatest level of uncertainty in LCA results, compared to transportation distances, material compositions, and low-energy process steps. Further study of the system boundaries and crediting strategies show that these methodological choices critically shape the outcomes of LCA results in a comparison of the EOL pathways. Overall, this work provides a quantitative representation of the environmental impacts for current and near-term technologies to manage retired wind turbine blades. The insights from this work can support more informed decision-making across the wind, cement, and glass industries as they respond to the growing volume of decommissioned blades.

A life cycle assessment of retired wind turbine blade management

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A life cycle assessment of retired wind turbine blade management

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