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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Material flows in the circular economy: Assessing the potentials of and limitations to the circularity of onshore wind turbines

A number of studies have analysed the environmental impact of the deployment of onshore wind turbines and their contribution to greenhouse gas emission reduction goals. Yet, little is known about the material flows at end-of-life (EOL) and their current state of recycling. The new concept of the Circularity Index (CI) includes the material recovery as well as energy requirements for recycling. In this dissertation, the Circularity Index will be used to further the understanding of end-of-life material flows of onshore wind turbines and assess to the potentials and limitations to their circularity.

To begin with, a review of relevant peer-reviewed articles, reports and wind turbine life-cycle assessments (LCAs) will provide an overview of previous research in this area. The review includes the Circular Economy (CE) principles, the role of onshore wind turbines and their material demand including rare earth elements (REE).

Afterwards, a material flow analysis (MFA) provides the information to create an excel database with the components and material information. Then, a general methodology for the CI calculation for technologies consisting of different materials will be described. The newly obtained database is used to estimate the Circularity Indices of three different 2 MW turbines. Furthermore, the material flows are visualised using Sankey diagrams. Finally, different strategies for improving the CI, its application as a benchmark, and recommendations for relevant stakeholders will be discussed.

The findings of the review indicate that the material demand for new wind turbines and REE cannot be supplied through recycled and reused material alone and that there are no circular material flows in the near future. This finding is also supported by the calculated CI values: the mass-weighted CI values for the 2 MW wind turbines are 2.2% (Enercon), 3.8% (Gamesa), 3.9% (Vestas WT). The energy-weighted CI values are slightly higher with 11.7% (Enercon), 13.7% (Gamesa), 14.7% (Vestas WT). The Sankey diagrams visualize the material flows of different wind turbines and highlight the gap between current and best practice of EOL management.

The results clearly indicate that the material flows of wind turbines are currently far from circularity. Moreover, a gap in the literature on EOL strategies exists and there is a big potential to divert EOL material flows from landfill to recycling. It is argued that, after small modifications and standardisation, the CI could be used as a benchmark for progress towards material flow circularity. Finally, different recommendations are presented, which include to (1) improve monitoring and reporting of EOL material flows, (2) investigate and incentivise the reuse of components, which are currently landfilled or recycled to avoid material losses and high energy demand for recycling.


Course Overview


The need to engage in better problem definition through careful dialogue with all stakeholder groups and a proper recognition of context.


An ability to work with specialists from other disciplines and professional groups acknowledging that technical innovation and business skills also must be understood, nurtured and combined as precursors to the successful implementation of sustainable solutions.


An understanding of mechanisms for managing change in organisations so future engineers are equipped to play a leadership role.


An awareness of a range of assessment frameworks, sustainability metrics and methodologies such as Life Cycle Analysis, Systems Dynamics, Multi-Criteria Decision making and Impact Assessment.