Repurposing EoL WTB Components into a Large-Scale PV-Floating Demonstrator

7.73.3 Repurposing EoL WTB Components into a Large-Scale PV-Floating Demonstrator Mário Moutinho, Ricardo Rocha, David Atteln, Philipp Johst, Robert Böhm, Konstantina-Roxani Chatzipanagiotou, Evangelia Stamkopoulou, Elias P. Koumoulos and Andreia Araujo Special Issue Wind Turbine Decommissioning: Dismantling, Demolition, Recycling, Reuse and Repurposing Edited by Dr. Lawrence C. Bank and Dr. Paul Leahy Article https://doi.org/10.3390/su17198717 Academic Editors: Lawrence C. Bank and Paul Leahy Received: 5 August 2025 Revised: 19 September 2025 Accepted: 26 September 2025 Published: 28 September 2025 Citation: Moutinho, M.; Rocha, R.; Atteln, D.; Johst, P.; Böhm, R.; Chatzipanagiotou, K.-R.; Stamkopoulou, E.; Koumoulos, E.P.; Araujo, A. Repurposing EoL WTB Components into a Large-Scale PV-Floating Demonstrator. Sustainability 2025,17, 8717. https://doi.org/10.3390/ su17198717 Copyright: © 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). Article Repurposing EoL WTB Components into a Large-Scale PV-Floating Demonstrator Mário Moutinho 1, Ricardo Rocha 1, David Atteln 2, Philipp Johst 2, Robert Böhm 2, Konstantina-Roxani Chatzipanagiotou 3, Evangelia Stamkopoulou 3, Elias P. Koumoulos 3 and Andreia Araujo 1,4,* 1INEGI—Institute of Science and Innovation in Mechanical and Industrial Engineering, Campus da FEUP, R. Dr. Roberto Frias 400, 4200-465 Porto, Portugal; [email protected] (M.M.); [email protected] (R.R.) 2Faculty of Engineering, HTWK Leipzig—University of Applied Sciences, Karl-Liebknecht-Straße 132, 04277 Leipzig, Germany; [email protected] (D.A.); [email protected] (P.J.); [email protected] (R.B.) 3IRES—Innovation in Research & Engineering Solutions SNC, 1000 Brussels, Belgium; [email protected] (K.-R.C.); [email protected] (E.S.); [email protected] (E.P.K.) 4LAETA—Associated Laboratory of Energy, Transports and Aeronautics, Campus da FEUP, R. Dr. Roberto Frias 400, 4200-465 Porto, Portugal *Correspondence: [email protected] Abstract The growing volume of decommissioned wind turbine blades (WTBs) poses substantial challenges for end-of-life (EoL) material management, particularly within the composite repurposing and recycling strategies. This study investigates the repurposing of EoL WTB segments in a full-scale demonstrator for a photovoltaic (PV) floating platform. The design process is supported by a calibrated numerical model replicating the structure’s behaviour under representative operating conditions. The prototype reached Technology Readiness Level 6 (TRL 6) through laboratory-scale wave basin testing, under irregular wave conditions with heights up to 0.22 m. Structural assessment validates deformation limits and identifies critical zones using composite failure criteria. A comparison between two configurations underscores the importance of load continuity and effective load distribution. Additionally, a life cycle assessment (LCA) evaluates environmental impact of the repurposed solution. Results indicate that the demonstrator’s footprint is comparable to those of conventional PV-floating installations reported in the literature. Furthermore, overall sustainability can be significantly enhanced by reducing transport distances associated with repurposed components. The findings support the structural feasibility and environmental value of second-life applications for composite WTB segments, offering a circular and scalable pathway for their integration into aquatic infrastructures. Keywords: wind turbine; wind turbine blades; decommissioning; repurposing; life cycle assessment (LCA) 1. Introduction The expansion of wind energy plays a pivotal role in the decarbonisation of global energy systems. However, this rapid growth also presents a significant challenge: the disposal of end-of-life (EoL) wind turbine blades (WTBs). These WTBs, typically composed of thermoset glass fibre-reinforced polymers (GFRPs), are designed to exhibit high strength, low weight, and high durability [ 1 ]. However, recycling WTBs presents a significant challenge. Sustainability 2025,17, 8717 https://doi.org/10.3390/su17198717 Sustainability 2025,17, 8717 2 of 29 Their complex composite structures are inherently resistant to degradation and difficult to separate into reusable constituents. As a result, recycling processes are both energyand cost-intensive [ 2 ]. Despite increasing environmental and regulatory pressure to adopt alternative disposal methods, landfilling remains the predominant practice in many regions [ 3 , 4 ]. By the year 2050, it is estimated that Europe alone will generate 7.6 million tonnes of EoL WTB materials [5], with worldwide estimates exceeding 43 million tonnes [6]. This growing material stream has led to a surge of interest in circular economy (CE) solutions for EoL WTB materials. The CE framework is focused on reducing the use of virgin materials and extending the life span of products through R-strategies, namely reuse (R3), repair (R4), refurbish (R5), remanufacture (R6) and repurposing (R7) [ 7 , 8 ]. It is further emphasised that these strategies are not mutually exclusive but can support each other in combined approaches [ 9 ]. The strategy of structural repurposing—where EoL WTB materials are used in a new application with a different function—is gaining recognition as one of the most promising EoL strategies for WTBs as stated in, e.g., [10,11]. Recent studies have demonstrated the potential for structural repurposing in a variety of domains. As part of the Re-Wind network (https://www.re-wind.info/), full-scale bridges using decommissioned WTBs have been constructed as prototypes [ 12 ] and, in addition, applications in noise barriers and transmission poles [ 13 ] have been investigated. In the context of the EuReComp project (https://eurecomp.eu/), recent studies have explored the integration of EoL WTB segments into PV-floating systems. This innovative concept has been examined on a small scale [14,15]. As demonstrated by the cited applications, repurposing practices can significantly divert EoL WTB material from landfilling. The extent of this diversion depends on the specific R-strategy employed. For instance, complete repurposing can theoretically achieve 100% diversion by capitalizing on the blade’s intact structural integrity [ 16 ]. Beyond waste reduction, repurposing has been shown to offer both environmental and economic benefits, including material preservation, emission reductions, and decreased demand for virgin resources [ 17 , 18 ]. For example, diverting just 20% of WTB material through repurposing strategies may prevent approximately 135 tonnes of composite waste from entering landfills annually, while also reducing carbon emissions by an estimated 30,780 kg of CO 2 -equivalent per year [19]. Nevertheless, the field of repurposing faces considerable challenges. The structural diversity and complexity of WTBs contribute to high variability in the EoL material stream, complicating segmentation, handling, and integration into new applications. From a Life Cycle Assessment (LCA) perspective, the primary environmental burdens are associated with the energy required for blade segmentation processes and transportation activities [ 20 ]. The availability of standardised design methods and scalable applications is limited (e.g., highlighted in [21,22]). This study addresses this gap by presenting, in contrast to a previously built small scale PV floating system, a functional, upscaled demonstrator that repurposes EoL WTB segments from an Enercon E66 wind turbine into floats for a large-scale PV-floating system, supported by numerical simulation and comparative LCA. This concept integrates two renewable energy sources—wind and solar—into a single circular system, while addressing the issue of EoL WTB material stream. During the manufacturing process, the repurposing strategy (R7) is combined with repair (R4) and refurbishing (R5) activities. The demonstrator’s incorporation of EoL WTB components, including spar caps and shear webs, is driven by the objective of enhancing the proportion of repurposed EoL WTB materials. The demonstrator achieved Technology Readiness Level 6 (TRL 6) through laboratory testing under controlled environmental conditions. The design process was supported by a calibrated numerical model aimed at replicating the physical behaviour under rep- Sustainability 2025,17, 8717 3 of 29 resentative use-case scenarios. This model served as the foundation for simulation-based structural analysis, with the goal of informing future design refinement and supporting potential scale-up and deployment scenarios. Furthermore, LCA was conducted to evaluate its environmental performance. By addressing issues of design complexity, validating mechanical and environmental performance, and maximising material repurposing, this study supports the transition towards circular solutions for EoL WTB materials and offers new pathways for scalable innovation. 2. Materials and Methods The investigation of repurposed applications for EoL WTBs followed a multidisciplinary approach structured around four interdependent pillars, as summarized in Figure 1. The process begins with material sourcing and digitalisation of the EoL WTB sections, which provided the foundation for the design and fabrication of a physical demonstrator—a PV-floating platform integrating sections of an EoL WTB. The fabricated structure is subsequently subjected to full-scale experimental testing under realistic use-case conditions to evaluate its performance and quantify the maximum loading conditions under representative scenarios. In parallel, finite element numerical simulations are carried out and iteratively calibrated with experimental data to assess stress distributions under worst-case boundary conditions and guide potential structural optimisations. Finally, a preliminary LCA is conducted to evaluate the environmental impact of the proposed solution and benchmark its sustainability against conventional alternatives.  Designand Fabrication Experimental Testing Numerical Simulation LCA Material Sourcingand Digitalization Figure 1. Flowchart of methodology adopted. 2.1. PV-Floating Demonstrator Design for Circularity 2.1.1. Material Sourcing from an EoL Enercon E66 WTB Decommissioned Enercon E66 WTBs, measuring 33 m in length, were recovered after completing their 20-year operation life cycle at Ihlow, Germany, where they were dismantled and transported to Portugal. These WTBs are constructed using glass fibre, thermoset resin and adhesive, while the core includes balsa wood and aluminium. The combination of fibres and resin represents the majority of the WTB material composition. According to Jensen and Skelton [ 23 ], the proportion of reinforcing fibres and resin by weight is approximately 60–70% and 30–40%, respectively. In the initial phase, structural segmentation of the WTB was employed based on the structural and geometric specifications of the E66 model. A typical WTB presents a twist angle that varies along the midspan relative to the radial position from the rotor hub, with the angle becoming more uniform toward the blade tip [ 24 ]. This more consistent geometry, combined with the smaller chord length (profile width), aligns with the requirements for both easy transport and the creation of a relatively level surface suitable for the PV platform base. Furthermore, WTBs experience lower lifetime fatigue loading closer to the tip compared to the root section, which may help preserve their original mechanical properties for second life applications [ 25 ]. For this reason, the section selected as most promising Sustainability 2025,17, 8717 4 of 29 for the first design iteration was a 7.5 m segment, starting at 8 m from the tip (Figure 2), offering an optimal balance between structural integrity and geometric uniformity. Figure 2. Cutting process for extracting WTB segments and spar cap beams from EoL WTBs: (a) TD cuts, (b) cross-section, and (c) LD cuts. For this study, three 7.5 m EoL WTB segments from dismantled E66 turbines were cut on the transverse direction (TD) using a handheld cement saw equipped with a diamond blade (Figure 2a). One segment (sg_A) was used for digital 3D scanning to support design work, while the remaining two (sg_B, sg_C) were allocated for the demonstrator fabrication. After scanning segment sg_A, longitudinal direction (LD) cuts were carried out using a jigsaw to extract the shear web and spar cap beam components, following the method described in [ 26 ]. This segmentation process is illustrated in Figure 2c, with section A-A shown in Figure 2b highlighting the internal blade structure. In the demonstrator, segments sg_B and sg_C were repurposed as floaters forming the base of a platform designed to support four PV panels. The ends of the blade segments were sealed using the previously extracted shear web components as cover lids, bonded in place through hand layup with reinforcing fibres. The spar cap beams were then used to construct the PV support structure. 2.1.2. Geometrical Characterization of EoL WTB Segments Initially, one of the three 7.5 m WTB segments was subdivided into three consecutive 2.5 m sections to enable digital reconstruction. Surface geometry acquisition was performed using a HandySCAN 307 (Creaform, Lévis, QC, Canada), which generated a series of cross-sectional profiles (Figure 3a) for reconstructing the full surface geometry using boundary surface modelling in SolidWorks (Version 2025 SP3.0, Dassault Systèmes SE, Vélizy-Villacoublay, France). The resulting 3D model (Figure 3b) was subsequently validated against physical measurements obtained from the original segment, including chord length, leading and trailing edge curvature, and thicknesses, also represented as an example on the cross-sectional profile displayed on Figure 3c. Sustainability 2025,17, 8717 5 of 29    Figure 3. Geometric characterisation of E66 WTBs, (a) WTB scanned stations’ profiles, (b) WTB segment with dimensions, (c) cross-sectional profile of the blade at 15.5 m from tip. 2.1.3. Design Steps and Support Integration The PV system consists of four standard-sized PV panels (15 kg each, 1.68 m ×1.0 m ) arranged in a two-by-two configuration (2 columns × 2 rows). The minimum required length of the WTB segments was determined by the space required to accommodate two PV panels placed side by side, resulting in a total of at least 3.4 m. For the structure’s width, both panel dimensions and a 40 ◦ tilt angle (identified as optimal for Porto, Portugal [ 27 ]) were considered, along with shadow-casting shadows effects. This yielded a minimum required width of 2.1 m. A schematic representation of the combined PV array and WTB-based floating structure is shown in Figure 4to illustrate the general layout and installation arrangement.  Figure 4. Schematic representation of preliminary concept design of WTB floats for PV panels. The optimal configuration was established based on project-specific design objectives, balancing structural requirements with energy performance considerations. These criteria achieve the following: (i) minimizes gaps between the overlapping segments of two identical WTBs; (ii) allows the connection between the supporting structure and the WTB spar cap, which is the most rigid area; (iii) provides the flattest possible surface on top to support the PV structure; (iv) maintains a segment length of approximately 3.4 m; (v) ensures that the combined width of the two WTB segments prevents front PV panels from casting shadows on those behind. Two possible concepts were evaluated. In the first hypothesis, the widest portion of one WTB segment overlapped with the narrowest portion of the other. In the second, the widest portions of both segments overlapped, as shown in Figure 5. After rotation and positioning adjustments, the second configuration (Figure 5b) was selected, as it offered Sustainability 2025,17, 8717 6 of 29 reduced assembly gaps, a broader support surface for the PV structure, and simplified structural connections.  Figure 5. Hypothesis for overlapping two WTB segments. In (a), hypothesis one, the short width overlaps with the long width. In (b), hypothesis two, the long width overlaps with the long width. Considering the assembly clearances, the final WTB segment dimensions were set to 1.4 m in width at one end and 1.8 m at the opposite end, with a total length of approximately 3.6 m, as illustrated in Figure 6.  Figure 6. Final segmentation after the design. The centre of mass (CM) of the WTB segments was estimated experimentally using a trial-and-error approach, where each segment was lifted both in the LD and TD until it could be safely hoisted in a level position (Figure 7).  Figure 7. Experimental characterization of the centre of mass. (a) LD direction CM giving the X position where the straps balance the WTB; (b) is the same as (a), confirming the X position of CM; (c) TD direction CM giving the Y position where the straps balance the WTB. The experimental characterization of the selected segment’s CM yielded LD X 1.77 m and TD Y 0.95 m, out-of-plane Z 72.9 mm, with the coordinate system origin set at the tip of the leading edge on the wider side. Based on the CM of each WTB and assuming a spar cap beam density of 1.8 kg/dm 3 , the overall CM of the floating demonstrator was determined. Sustainability 2025,17, 8717 7 of 29 To evaluate static equilibrium in floating conditions, the demonstrator was iteratively sectioned by a hypothetical horizontal plane parallel to its base, representing the waterline. The submerged section generates defines the displaced volume and thus the buoyant force, which equals the weight of the displaced water, in accordance with Archimedes’ principle. The support structure, depicted in Figure 8, functions both as the primary mounting system for the PV panels, and as the connecting frame that secures the two EoL WTB segments used as floats. This structure was designed to ensure stability and rigidity by using unidirectional (UD) fibre-reinforced spar cap beams extracted from EoL WTB segments (Figure 2c). This approach contributes to the system’s sustainable design and aligns with CE principles [7].  Figure 8. Support structure for the WTB segments as floaters and PV panels. The framework consists of rectangular spar beams measuring 50 by 20 mm, arranged in a grid-like platform. Spar caps are traditionally engineered to withstand tensile and compressive loads along the LD of WTB and to transfer wind-induced bending moments to the rotor hub. Even after decommissioning, they retain considerable mechanical strength and stiffness, as demonstrated by Alshannaq et al. [ 28 ]. These favourable properties were also confirmed in [ 29 ], making them well-suited for integration into the support structure [26]. The final design of the full-scale PV-floating demonstrator is illustrated in Figure 9. Figure 9. Design of the repurposed PV-floating demonstrator. 2.2. Demonstrator Assembly 2.2.1. Repair Methods to Ensure WTB Segments Floatability The EoL WTB segments were visually inspected to identify defects requiring localized repair. While sufficient for feasibility assessment, visual inspection cannot detect Sustainability 2025,17, 8717 8 of 29 subsurface or fatigue damage; thus, practical deployment would require non-destructive testing ( e.g., ultrasonic , thermographic, or acoustic emission) to ensure long-term structural integrity under hydrodynamic loads. Surface abrasion [ 30 , 31 ] was conducted with a pneumatic orbital sander (80-grit) to remove the weathered surface layer and surface residues. The process was carefully controlled to avoid exposing laminate layers or removing structural material. Local defects such as surface scratches, shallow dents, and holes up to ~5 mm in diameter were repaired using a two-component epoxy putty, applied and shaped to match the surrounding surface, and cured at room temperature. The same epoxy putty was used to seal areas where the laminate was exposed from transport or cutting operations, providing a protective barrier against moisture ingress and environmental degradation. After curing, repairs were sanded with 120-grit abrasives for surface uniformity. All edges and cut ends of the WTB segment were chamfered to reduce sharp transitions and minimize stress concentration. Shear web components were cut to size and used as lids for the WTB segments (boundary joints hand laminated using glass fibres and epoxy resin). Finally, the entire segment was coated with a waterproof maritime-grade paint (SEA-SPEED ® V10X ULTRA CLEAR, Pinehurst, TX, USA) to enhance durability in aquatic environments, consistent with its intended function as a floating support element in the demonstrator. 2.2.2. PV-Floating Demonstrator Assembly Assembly followed the procedures outlined in Section 2.1. After sealing the ends and applying the protective coating, the two WTB segments were positioned with a crane and overlapped longitudinally to form the platform geometry. TD spar cap beams were bolted across both segments to secure alignment, with silicone applied at bolt interfaces to ensure watertightness. The remaining support structure components were mounted using bolted connections, and the PV panels were then installed, completing the demonstrator assembly, as depicted in Figure S1 in the Supplementary Information. 2.3. Experimental Setup and Testing Methodology The demonstrator was assembled and tested in the wave basin of the Hydraulics Laboratory at the Faculty of Engineering of the University of Porto (FEUP). The facility measures 28 × 12 × 1.2 m and is equipped with active wave absorption and a dissipating beach to minimize re-reflections. Waves were generated with a 16-paddle HR Wallingford piston-type wavemaker, capable of producing regular, irregular, and short-crested conditions. The objective was to evaluate demonstrator’s performance under representative aquatic environments such as lakes, reservoirs, and rivers. Wave elevation was measured using four resistive-type wave probes (WP). Two probes were placed upstream of the demonstrator in sequence to characterize the incoming wave field, and another two were positioned laterally on either side of the demonstrator (Figure 10). This setup allowed assessment of the wave–structure interaction, as well as reflection and transmission effects with the tank boundaries. All probes were calibrated prior to testing and managed using the HR DAQ Suite software, which was also employed for post-processing the free surface elevation time series. A Qualisys motion tracking system was utilized to record demonstrator motions in real time across all six degrees of freedom (DoF). Three elevated cameras faced the wave tank to create an accurate volume measurement. Infrared markers were placed on the PV panels following manufacturer guidelines, and the demonstrator was digitally defined as a “rigid body.” Calibration tests were repeated daily or whenever residuals exceeded 0.5 mm, ensuring measurement reliability. Data was acquired at 100 Hz, matching the wave probes. Diagonal tension cables reinforced the demonstrator, providing stability under Sustainability 2025,17, 8717 15 of 29 In contrast, roll spectrum displays a series of smaller peaks distributed over a broader frequency range, with no significant variation across wave directions. This broadband behaviour suggests that roll motion is less sensitive to wave heading and likely driven by a combination of directional spreading and platform asymmetry, rather than distinct modal excitation. Finally, the yaw response presents a broader spectral distribution, with significant energy content concentrated at low frequencies, without identifiable secondary peaks. This behaviour indicates a quasi-static or slowly varying yaw motion, rather than a dynamic resonance phenomenon. Despite the absence of sharp spectral features, the yaw response reaches substantial angular excursions, with peak amplitudes reaching 83.7 ◦ under Oblique wave conditions and 74.8 ◦ in the Frontal case. The persistence and magnitude of these oscillations are of particular concern, as yaw misalignment directly affects the orientation-dependent efficiency of PV modules by altering the angle of solar incidence. These findings emphasize the critical role of yaw stability in the design of PV-floating platforms. Passive yaw-damping solutions or directional mooring strategies should be considered essential to minimize rotational drift and optimize long-term energy yield under realistic operation conditions. Figure 14. PSD for Water Level Height on Lateral configuration under irregular waves. Regarding structural assessment, the spectral content and corresponding motion amplitudes indicate that dynamic amplification is primarily governed by first-order wave effects. Given the absence of high-frequency energy and the predominance of low-frequency, quasi-static motions, it is reasonable to consider a static or quasi-static numerical simulation approach to estimate structural stresses. This is particularly valid if the worst-case accelerations—extracted from the recorded motion data—are used as conservative boundary conditions. Such simulations can provide reliable upper-bound estimates of loading, especially in preliminary design stages or when evaluating structural safety margins under extreme but infrequent operation conditions. Sustainability 2025,17, 8717 16 of 29 Figure 15. PSD during irregular wave test for three demonstrator configurations: Frontal (FRT), Lateral (LAT) and Oblique (OBL) considering (a) surge, (b) roll, (c) pitch and (d) yaw. 3.2. Numerical Simulation Results of the Environmental Conditions of the Demonstrator The results of the conducted simulation are structured to feature the following: (i) Maximum displacement, (ii) Inverse Reserve Factor (IRF) utilizing Puck, Cuntze, and Maximum Stress for the spar cap beam support structure. Additionally, the results are compared to a demonstrator with fewer beams, to assess the potential for optimising material usage. The total deformation reaches a maximum of 12.7 mm in the reduced-beam configuration (Figure 16a) and 9.8 mm in the standard configuration (Figure 16b). In both cases, the maximum deformation occurs in the support structure of the solar panels. However, the assembly with fewer beams additionally suffers from higher deformation in the front. In this region, the overall bottom supporting structure is less rigid than the one with four additional beams. When looking at the IRF, a similar effect can be observed. In every location, except one on the top left, the factor is higher for the assembly with fewer beams (Figure 17a). Figure 17b shows the configuration with the full number of beams, which generally results in lower factors. Because the configuration with fewer beams shows significantly higher IRF and deformation, the following work focuses solely on the demonstrator with the full number of beams. Sustainability 2025,17, 8717 17 of 29 Figure 16. Total Deformation (in mm) of the two assemblies: (a) with fewer beams used (b) with full number of beams. Figure 17. IRF of the two assemblies. (a) With less beams used. (b) With full number of beams. Figure 18 highlights four regions of interest that exhibit relatively high IRF values. In Figure 18a, the maximum reaches 0.63, suggesting the potential for local damage. This value is associated with the Puck failure criteria, which identifies matrix-dominated failure near the bolt fixating region. Figure 18b shows a local IRF of 0.583, interpreted using the Cuntze matrix failure criterion. Although, this value remains below critical thresholds, it reflects locally elevated matrix stresses due to bending and contact interaction with an adjacent beam. A similar trend appears in Figure 18c, where the IRF reaches 0.72, again indicating matrix stress concentrations. This value corresponds to a bonded contact between the solar panel and the supporting beam. Although this result is higher than in other regions, it appears consistently across all panel–beam contact areas and may be attributed to localized contact modelling effects. Finally, Figure 18d displays IRF of 0.628, also classified under the Cuntze criterion, which results from a combination of bending moments and contact interactions with an adjoining beam. Sustainability 2025,17, 8717 18 of 29 Figure 18. Detailed view of the IRF of the final assembly: (a) Bottom spar cap beam connecting bolt load area. (b) Side spar cap beam showing a bending load. (c) Spar cap beam in bonded contact with the solar panel. (d) Smaller spar cap beam in the corner showing a bending load. In the full assembly, the numerical analysis identifies potential failure zones that warrant careful monitoring to ensure long-term integrity. The following improvements for future designs of the demonstrator are proposed: (i) To mitigate high IRF values near the connection bolts of the WTB segments, a higher number of bolts should be introduced to distribute the load more evenly. Additionally, the use of Class 12.9 Hex Bolts is recommended, as internal stresses in the bolts can be high (see Figure S3)). (ii) Plastic end caps connecting the side and bottom spar cap beams could be added for additional reinforcement purposes. (iii) If less lateral flexibility in the solar panel structure is desired, lowering the height could save material, increase more rigidity, and offer less contact area for additional wind loads in aquatic conditions. (iv) A lower height combined with wider spar cap beams could also reduce bending stresses in the corner beams. 3.3. LCA of Repurposed Floating Demonstrator LCA was performed on the repurposed structure, and the results were expressed over the 16 impact categories of the Environmental Footprint method. Figure 19 presents the contribution of each type of input and output, along the life cycle of the system. Different components had a different contribution to the impacts but overall, the analysis reveals that the steel used, tooling and machining, surface coating, inbound transport, and EoL treatment were major contributors to the total impacts. Steel has a significant contribution ( ≥ 20%) to the impact categories of human toxicity (CT and NT), MR and FE. NC potential from the upstream production of steel is primarily linked to Lead (II) emissions to air (10% of total impacts per m 2 ), as part of the upstream process of Ferronickel production along the life cycle of steel (25% of total Lead (II) emission impacts per m 2 ). Environmental pollution with Lead along various stages of Ferronickel production have been previously reported [ 51 , 52 ]. CT from the upstream production of steel is primarily due to Antracene emissions (36% of total CT impacts), associated with coke production (i.e., an industrial fuel produced from hard coal), responsible for 37% of total anthracene emission impacts per m 2 of repurposed structure. Finally, chromium Sustainability 2025,17, 8717 19 of 29 depletion for the upstream production of steel (modelled as hot-rolled chromium steel) had a significant contribution to MR impacts (37% of MR impacts per repurposed system).  Figure 19. LCA outcomes for repurposed structure: contribution (%) of different inputs and outputs throughout the system’s life cycle to the overall impacts for different impact categories. In the comparative LCA, the repurposed structure was compared with two conventional PV floating structures described in the literature: conventional structure A [ 40 , 41 ] and conventional structure B [ 40 , 41 ]. The contribution of different components to the total weight of the structure for the three analysed systems is shown in Table 2. Furthermore, the contribution of each component to CC impacts is also shown for the different structures. The composition of the repurposed structure in terms of main components resembles the one for conventional structure A, with the floating structure components having a major contribution to the weight (>90%), while steel does not exceed 3%. It should be noted that the Ecoinvent process to model steel for the repurposed structure and conventional structure B (i.e., chromium steel) was different than the library process used for conventional structure A (low alloyed steel and its processing), with the latter having lower impact per kg of steel in most impact. Using low-alloyed hot-rolled steel instead of chromium steel to model the overall impacts of the repurposed structure results in over 10% decrease of impacts for several impact categories (AP, FE, NT, IR, MR), with up to 41% increase for MR impacts, whereas ET and CT impacts increase by 7% and 24%, respectively. Therefore, a more careful selection of proxy for the steel components should be considered. This selection should reflect the intended service environment (i.e., long-term structural support in aquatic conditions over 30 years) and account for relevant required material properties, particularly corrosion resistance. Tooling and machining also contributed significantly ( ≥ 20%) to several impact categories, namely FE, IR, and OD (Figure 19). For EF, the main source was the surface abrasion process (17% of impacts per m 2 of system), largely due to compressed air use, which accounted for over 80% of total impacts in all categories per hour of surface abrasion. FE was mainly associated with phosphate emissions to water, linked to spoil treatment from hard coal and lignite mining, i.e., two key inputs in the upstream electricity generation for compressed air production (87% of total FE impacts per hour of surface abrasion). Similarly, electricity consumption for compressed air production was the dominant source of IR impacts (99% contribution per hour), largely due to the treatment of uranium milling Sustainability 2025,17, 8717 20 of 29 tailings from the production of nuclear electricity used in the European grid. A combination of various sources was used to model surface abrasion, as a suitable proxy for treatment of composite material surfaces was not available in the Ecoinvent library (Table 1). To place the achieved results in context, an abrasive blasting process for carbon steel using alumina as the abrasive agent was selected as an alternative proxy from Ecoinvent, and the total impacts per m 2 of repurposed structure were calculated. Compared to the system modelled as reported in Table 1, the Ecoinvent library proxy for surface abrasion results in significant increase in all impact categories, ranging between 23% (for OD) and over 400% increase (for FE and IR). For this proxy from Ecoinvent, the sub-processes contributing primarily to impacts are similar as for the process modelled here (i.e., compressed air and electricity use). Overall, considering the high variation between the impacts of the selected and alternative proxy, it is advisable to calculate the actual energy and compressed air use for the tools employed in the construction of the demo, for a more reliable assessment of the impacts of the process. Besides surface abrasion, other employed tools during stage A5 also had a significant contribution to impacts. Namely, OD impacts stemmed primarily ( 44% per m2surface ) from the cutting of shear web components during stage C1. Nearly all of these impacts (>99% per m 2 ) were traced to tetrafluoroethylene, used to model a protection net within the inventory for stone cutting with diamond wire technology [ 44 ]. While informative, the overall contribution of machining should be interpreted with caution, as process-specific impacts of proxy data must be evaluated on a case-by-case basis, according to the actual cutting or surface treatment equipment and its corresponding LCI. Table 2. Weight percentage of different components per structure, and calculated CC contribution to the overall structure impacts. Indicator Conventional Structure A Conventional Structure B Repurposed Weight percentage steel (%) 3% 30% 2% Contribution to CC of steel (%) 1% 24% 8% Weight percentage plastic/WTB parts (%) 92% 70% 95% Contribution to CC of plastic/WTB parts (%) 55% 44% 0% Weight percentage coating (%) n.a. n.a. 3% Contribution to CC of coating (%) n.a. n.a. 8% Total structure weight (per m2)12.4 kg 20.3 kg 109 kg Contribution to CC of EoL plastic/WTB parts (%) 38% 31% 47% Contribution to CC of WTB/plastic parts inbound transport (%) <1% <1% 26% Contribution to CC of tools (%) n.a. n.a. 5% The surface coating of the repurposed structures had a measurable contribution ( ≥20% ) to the impact categories of FE, OD, ET, and WU (Figure 19). Among the different coating components, the waterproof maritime-grade coating was the largest contributor (over 70% of total coating impacts) in every impact category. For ET, several of the components in the coating, and their corresponding upstream production, had a significant contribution ( ≥ 20% per Litre of coating) to impacts, namely Hexamethyldisilazane (HMDS), Tetraethyl orthosilicate, and Bisphenol A epoxy resin. FE per Litre of coating was primarily due to the upstream production of propanol (50% of impacts) and HMDS (26% of impacts per Litre of coating). OD potential per Litre of coating was primarily (90%) due to the upstream production of HMDS, and more specifically the emissions of Sustainability 2025,17, 8717 21 of 29 Dichlorodifluoromethane (85% of impacts per Litre of coating) during the production of the Methylchloride included in the LCI of HMDS. Finally, WU impacts per Litre of coating were also primarily (over 55% per Litre of coating) due to the upstream production of HMDS. It should be noted that the commercial two-component silane siloxane maritime-grade nano coating used during the construction of the demo could not be modelled based on its ingredients, as only the hazardous components were disclosed in the corresponding Material Safety Data Sheet (i.e., Dibutyltin Dineodecanoate, 3-Aminopropyltriethoxy silane), which contributed to less than 15% of the total mass of the product. Instead, a previously published LCA study on an anti-corrosion coating for maritime applications was used as source of LCI data for the coating’s composition [ 43 ]. In addition, several proxies were selected to model this composition, as the actual ingredients were not available in the Ecoinvent library (i.e., HMDS instead of 3-Glycidyloxypropyltrimethoxysilane, Bisphenol A epoxy instead of Poly (bisphenol A-co-epichlorohydrin) glycidyl end-capped, Methyl ethyl ketone instead of Acetil acetone, and Titanium Dioxide instead of Titanium isopropoxide). Interestingly, while the two studies considered here for the conventional structures did not analyse the impacts of the coating (Table 2), Hayibo et al. [ 53 ] included a polyurethane marine sealant in their assessment of a floating structure for PV panels, which had a significant contribution to both the weight (67% of total materials) and environmental impacts (up to 94% contribution to the total system’s impacts, for ET). Considering their significant contribution to the overall impacts, the composition of protective coatings, and the selected proxies to model its individual ingredients, should be better evaluated on a case-by-case basis for the specific application (i.e., for surfaces exposed to water), both for future studies on EoL component repurposing applications, but also, in general, for LCA on structures exposed to seawater during their use phase, which require the use of coating. The transportation of decommissioned components from the original location of the WTB (Germany) to their final installation site (Portugal) (i.e., stage A4), over a distance of 2310 km, had a significant contribution ( ≥ 20%) to most impact categories (Figure 19). These impacts are partially depended on how the transport process was modelled. For example, when the European market process from Ecoinvent used to model the transport of repurposed components is switched from EURO4 (current scenario) to EURO6 ( i.e., adhering to more strict regulations regarding emissions), significant decrease of up to 37% is calculated for AP, OF, ME and TE impacts per m 2 of PV surface. Furthermore, when the lorry size is changed from 16–32 metric tonnes (current scenario) to 3.5–7.5 metric tonnes, all impact categories exhibit increase in impacts by up to 49%, whereas switching to a larger capacity lorry (>32 metric ton) results in decrease in all impacts by up to 13%. Therefore, the selection of an accurate process to model transportation as realistically as possible is important, to decrease the uncertainty of the calculated results. Besides the process used to model transportation, an alternative scenario was also investigated related to the transportation distance, assuming that the construction of the PV-floating structure takes place closer to the original location of the EoL WTB (100 km distance). The corresponding decrease in impacts per m 2 of repurposed structure was calculated, as shown in Figure 20. Measurable decrease, ranging between 12% (for WU) and 57% (for LU), can be observed for all impact categories. Considering the large weight of decommissioned components used here, compared to alternative designs of floating PV installations (Table 2), it is important to optimize the distance of the source material to the installation site, in order for repurposing applications of WTB components to remain environmentally competitive with the use of (virgin) plastic material for floating structures. Overall, different alternative repurposing strategies for EoL materials from WTB should be selected on a case-by-case basis, considering the original location of the materials, the distance from the envisioned location for the repurposed structure, and the application- Sustainability 2025,17, 8717 22 of 29 specific conditions and logistics of the final location (e.g., in this case, the solar irradiance for PV panels). Figure 20. Impact decrease for alternative inbound transportation scenario for WTB components. Finally, the EoL treatment process for the decommissioned components also had a measurable contribution to impacts, particularly (≥20%) for the ET, NT, and CC potential impact categories (Figure 21). The contribution of different sub-processes to the EoL treatment of WTB components (per m 2 of structure) is shown in Figure 19. All three impact categories are primarily (i.e., 71%, 63% and 62%, respectively) caused by the incineration of the resin and adhesive portion of the WTB segment (i.e., 25% of the 600 kg component), modelled as mixed plastic waste incineration. ET is primarily (71% of impact per kg of CFRP waste) caused by chloride emissions to water, likely associated with the presence of PVC in the mixed waste composition as modelled in Ecoinvent, which can result in the release of chlorine-containing pollutants [ 54 , 55 ]. NT (per kg of CFRP waste incinerated) is primarily due to Mercury (II) emissions to air and Arsenic ion emissions to water (34% and 37% of total impacts per kg of waste, respectively), released during the incineration of mixed plastic waste (81% of total Hg emission impacts), as has been previously reported [ 54 ], or during the landfilling of residual waste from mixed plastic incineration (91% of total As emission impacts), respectively. Finally, per kg of CFRP material being incinerated, 95% of the CC impact is due to CO 2 emitted during mixed plastic waste incineration. Considering the significant contribution to impacts of the EoL treatment process, an alternative scenario was investigated as part of a sensitivity analysis, wherein all waste was diverted to a sanitary landfill, instead of incinerated. Per m 2 of PV panel surface in the repurposed structure, landfilling results in less than 10% decrease for most impact categories, except for NT (11%), CC (48%) and WU (95% decrease), while for other impact categories the landfill process resulted in increase in impacts (33% for ME and over 150% for ET). These variations in environmental impacts under different alternative EoL treatment scenarios ought to be investigated, particularly considering the expected trends in EoL treatment technologies over the coming 30 years, which necessitate the use of prospective LCA methodology in order to predict and optimize the impacts of WTB component repurposing. Overall, considering the incineration scenario analysed here, per 1 system described here (6.72 m 2 PV surface), the EoL treatment of the repurposed components (including all the processes shown in Figure 21) corresponds to CC potential of 575 kg CO 2 eq, equal to the impacts of producing 185 kg of virgin polyethylene material (i.e., same material used for constructing Sustainability 2025,17, 8717 23 of 29 approximately 14 m 2 conventional structures). Such insights highlight the importance of diverting decommissioned components from waste treatment and developing strategies for the replacement of virgin materials with repurposed components. Figure 21. Contribution of different sub-processes to the EoL treatment of decommissioned WTB components (per m2of floating structure). The environmental impacts of the repurposed structure (per m 2 of PV surface) were compared to the two conventional structures from literature, and the results are shown in Figure 22. It should be noted that for both conventional structures, the protective coating is not included in the LCI (or at least not analysed separately from the plastic components). Similarly, the tooling required for stage A5 is also not included in the LCI. Therefore, the impacts of the repurposed structure are likely overestimated. Nevertheless, for most impact categories, the impacts of the repurposed structure (under the original transport scenario) are within range of the impacts calculated for the conventional systems. In fact, when the alternative inbound transport scenario is considered for the WTB components, the impacts closely follow those of the Conventional A structure, which uses a similar bill of materials in its construction as the repurposed structure (Table 2). Figure 22. Comparative assessment of conventional and repurposed structures (per m 2 ). Repurposed structures are analysed based on original transportation distance (DE-PT scenario, 2310 km) and alternative WTB component transport (100 km scenario). Conventional structures include 100 km transport scenario for used materials and generated waste. 4. Discussion The presented work demonstrates the feasibility of repurposing EoL WTB segments as floating structural elements for PV support platforms. The assembly process confirmed the Sustainability 2025,17, 8717 24 of 29 practical viability of adapting large-scale composite structures, originally designed for highperformance aerodynamic applications, into buoyant infrastructures. The overlapping of WTB segments and the use of existing structural features, such as spar caps, for integration proved effective in achieving mechanical stability and ease of assembly. Nonetheless, to better support the design, a detailed quantitative comparison of stress distribution, buoyancy performance, and material usage should be addressed in future work. The integration of experimental testing and calibrated numerical simulation enabled the identification of critical loading areas and informed recommendations for design optimization. Stress concentrations were observed near bolt connections and overlapping components but remained within acceptable limits under Puck and Cuntze failure criteria. Attention to contact conditions and boundary interfaces is recommended for future iterations, particularly in preparation for TRL 7 deployment in real environments. The simulation employed a simplified static load derived from experimental data, omitting dynamic amplification but capturing realistic inertial effects. Comparative results showed that the original configuration—with more spar cap beams—exhibited better structural performance. Attempts to reduce beam count without geometric redesign led to excessive deformation and IRF values, highlighting that material savings require deeper optimization rather than direct component removal. Future work should include simulations based on representative EoL material properties, employing appropriate prediction tools to improve accuracy and identify potential reinforcement needs. Comparative LCA results suggest that repurposed WTB components are a viable substitute for virgin plastics commonly used in floating PV structures. Demonstrators built with repurposed components exhibited environmental impacts comparable to conventional alternatives. Transport distances, however, were shown to strongly influence sustainability: minimizing the distance between turbine decommissioning sites and installation locations can substantially improve environmental performance. A similar service life (30 years, as stated in the Functional Unit definition) was assumed for both systems, but the longterm durability of repurposed components under aquatic conditions must be verified in future studies. A more detailed LCI for tooling and coatings is also needed, as these stages are underrepresented in the literature-based LCIs for conventional systems. This likely overestimates the demonstrator’s environmental footprint, suggesting that the actual benefits of replacing virgin plastics with repurposed WTB components could be greater than reported here. Despite these promising findings, several barriers must be addressed before industrialscale implementation. Economically, costs associated with reconditioning EoL WTBs— including transport, cutting, repair, and inspection—must be balanced against those of conventional materials. Technically, long-term evaluation in real-world environments is essential to ensure durability and safety. Logistically, scaling remains challenging due to the size and handling requirements of blade segments. Future research should therefore prioritize life cycle cost analysis, extended field testing, and the development of efficient logistics chains to bridge the gap between laboratory-scale demonstrators and industrial deployment. Overall, these results highlight both the potential and limitations of integrating repurposed composites into floating PV applications. Key considerations for scaling include design for disassembly, material compatibility, and regional resource availability. Addressing these factors will be critical for advancing toward serial production and embedding this concept within broader CE frameworks.