Quantifying circular economy pathways of decommissioned onshore wind turbines: The case of Denmark and Germany

Onshore wind turbines in Europe are increasingly reaching the end of their first lifecycle. Their pathways after decommissioning call for the establishment of circular supply chains (e.g. refurbishment or recycling facilities). Reliable component and material flow forecasts are particularly crucial for the development of blade-recycling capacity, as such facilities still need to be established. However, current forecasts assume a static decommissioning time and neglect a second lifecycle for the wind turbines and their blades, which has resulted in potential recycling quantities being over-estimated. This study overcomes these issues by (i) collecting empirical data on the circular economy pathways taken by decommissioned onshore wind turbines in the mature onshore wind markets of Denmark and Germany, and by (ii) proposing a new component and material flow forecasting model for the more reliable planning of blade-recycling capacity. The results reveal that ∼50–60 % of decommissioned onshore wind turbines in Denmark and Germany were exported mainly to other European countries. If the second lifecycle practices of the past are continued in the future, annual blade masses for domestic recycling are expected to range between ∼380–770 tonnes for Denmark and ∼4400–11,300 tonnes for Germany in the next ten years. This study finds that the threshold values of blade volumes for an economically viable blade-recycling facility can be reached in Germany with its large operating wind-turbine fleet, but the recycling of Danish wind turbine blades would have to rely on aggregating resource flows from other countries or industries. By modelling the cascading order of a sustainable circular economy and the EU Waste Hierarchy Directive, this study improves the decision-making basis for policy makers and companies to achieve sustainable resource use along the wind industry's entire value chain.