The Green Nacelle: pioneering natural-fibre composites in wind energy

The global wind energy industry is facing the fact that the first generation of wind turbines are about to reach their end of life. Well established recycling options for large-scale glass fibre composite structures are still scarce at this time and the industry needs to consider more sustainable materials for the next generation of wind turbines.

This project demonstrates how large composite structures such as a nacelle for an offshore wind turbine can be built with natural fibres and biobased resins instead of the conventional glass fibre reinforced construction. At the same time, this nacelle showcases how natural fibre composites (NFC) can be used for structural applications and components.

The pioneering new NFC nacelle was commissioned by DOT (Delft Offshore Turbine), a leading wind turbine R&D innovator who are part of the DOB-Academy based in Delft, Netherlands. Manufactured by NFC specialists Greenboats®, with composite materials from Sicomin and Bcomp, and engineering support from Judel/Vrolijk & Co, the Green Nacelle is reported to be the largest NFC structure built to date.

Showcasing the opportunities with natural-fibre composites

Greenboats has specialized in the engineering and manufacturing of natural-fibre composites for the last ten years, inspiring companies to rethink their composite solutions and move towards more sustainable options. With the Green Nacelle, the company and its customer DOT Power have demonstrated that the state of the art in renewable and bio-based composite materials, coupled with efficient composite processing techniques, can lower energy consumption in manufacturing and significantly improve the sustainability of large-scale wind energy components.

Based on the extensive NFC processing expertise developed in-house, Greenboats can reduce the CO2 emissions of a typical glass fibre-reinforced composite (GFRP) part by 60-80% over the product life cycle. In the case of the Green Nacelle, energy consumption in manufacturing has also been reduced by over 50% compared to a nacelle made with existing GFRP technology.

These important sustainability benefits are all realised without compromising the performance, quality, or durability of the final composite structure.

Optimizing the composite material mix and streamlining the process

The Green Nacelle measures around 7.3m long, 3.6m wide and 3.1m high, with a surface area of approximately 100m2. It was constructed in two parts, an upper and a lower section, each with a steel frame attached that allowed the two halves to be bolted together. A lifeline system was incorporated for safe access to the roof and an emergency exit is included at the back of the nacelle. A key innovation of the Green Nacelle build process was the panel-based assembly approach, with both sections of the nacelle being created from flat sandwich panels, saving the material and energy necessary to produce large mould tooling.

Sicomin, manufacturer of the market-leading GreenPoxy® range of bio-based epoxy resin systems, has worked with Greenboats for many years, supplying materials and on-site technical support via its German distributor Time Out Composite oHG. Sicomin supplied its DNV GL approved InfuGreen 810 resin system, which was used to infuse Bcomp’s ampliTex ™ flax fibre reinforcement fabrics and FSC-certified balsa wood cores of the nacelle’s main structural sandwich panels.

The award-winning range of ampliTex™ technical flax fabrics includes different weave patterns – bi-axial, twill and uni­directional (UD) formats – that deliver excellent mechanical properties with low environmental impact thanks to the flax fi­bres being CO2 neutral over their lifetime. For the nacelle project, Bcomp supplied twill-weave reinforcements for the main sandwich panels as well as bi-axial tapes for the panel joints.

“This project, along with other large panel NFC applications in wind, was ideal for InfuGreen 810. Its low viscosity is very impor­tant for processing, but the viscosity cannot be too low – if the resin flows too fast it can cause porosity. Even more important are the fibre wetting properties of the resin itself, and in this respect, InfuGreen’s performance is su­perior to a standard system, giving improved mechanical properties in the final structure,” comments Michael Thon from Time Out Composite, the German distributor for Sicomin.

Once the infused panels were trimmed and tacked together on the temporary supporting ribs, Sicomin GreenPoxy 33 resins were used for laminating and sec­ondary bonding flax reinforcing tapes and additional plywood bulkheads.

Finally, Sicomin’s SGi 128 intumescent bio-based FR gelcoat was applied to pro­vide a durable coating for the nacelle’s in­terior and exterior surface, with TopClear UV-resistant clear coats also used to protect the flax fibre feature stripe details.

“For a structure like the nacelle, it was crit­ical that we selected materials that process consistently and perform well in large-scale components, and this is where Sicomin are so strong,” noted Friedrich Deimann, founder and MD of Greenboats, when discussing material selection. “Their resins, gelcoats and clear coats meet our sustainability targets, and match our NFC ethos, with no compromise on performance. Most impor­tantly, when we need to scale up, they can really supply on an industrial level.”

Long-term evaluation of natural-fibre composites

Both Greenboats and Sicomin have extensive test data and experience from various NFC and bio-resin projects, with both their R&D teams cooperating with a number of research institutes and universi­ties to investigate topics such as the impact of saltwater, humidity, weathering and UV light on the performance of composites. As a result, the team has a very good idea of how the nacelle will perform, expecting the same or better ageing performance compared to conventional materials.

Greenboats will monitor the nacelle per­ formance over time, using their findings to develop a detailed long-term case study for large outdoor NFC structures.

End-of-life options for composites in the wind sector

With massive CO2 equivalent savings, renewable raw materials, and significant reductions in energy consumption during manufacturing, natural-fibre composites make a compelling argument for change even before a product reaches end of life.

With more than 2.5 million tons of com­posite materials in use in the wind sector globally, and the first generation of tur­bines now starting to come to the end of their operational lives, considerable focus is now aimed at addressing these issues.

Greenboats themselves have included sev­eral key end-of-life assumptions that are specific to natural-fibre composites in their life cycle analysis, as well as reaffirming the benefits of their panel-based approach.

“We believe strongly that a panel-based approach to component design and manufac­ture has massive benefits. Our vision includes the repurposing or upcycling of panel sections from retired NFC wind energy components, massively extending the useful lifespan of the materials,” commented Friedrich Deimann, Greenboats.

Finally, only at the absolute end of their life, NFC components can be shredded and separated in several steps. The shred­ded material can now be used in a pyrolysis process to produce synthetic gas, which is used to make methanol or replace conven­tional refinery products such as heavy oil in industrial furnaces (Source: Schmehl et al. 2008). But this is just an example of what is possible, and not a defined future. In addition, there exists the possibility for highly-efficient energy recovery within the standard waste management system.

Sowing the seeds for the increased adoption of NFCs in wind energy

The importance and relevance of the Green Nacelle project has certainly been noted by leading industrial players and the composites industry itself. Earlier in 2021, Greenboats, Sicomin and Bcomp were nominated as JEC Innovation Awards finalists, and since the nacelle was deliv­ered, Greenboats has received enquiries from a significant number of wind energy manufacturers.

Within the wind energy industry, a nacelle was the ideal first application for NFC materials because the structural loads were easier to manage, compared to a blade for example. And while the primary goal of the Green Nacelle project was to confirm the possibility of building a nacelle out of significantly more sustainable materials, Greenboats has stated that they now see significant promise for future adoption of NFCs in even larger components.

“We are convinced that we can engineer and build any size nacelle, even those for the industry’s largest turbines, using our panel-based process and NFC solutions,” comments Deimann. “Due to higher raw material costs and the manufacturing process being technically more advanced, the cost of production using NFC is roughly 20-30% higher than GRP. However, there is a recy­cling advantage using sustainable composites, and this advantage is likely to significantly in­crease in the future. We must think in five-year steps. We are sure that there will be at least a small-series production of NFC nacelles by the end of the decade. From 2030 onwards, NFCs could have a relevant market share in the nacelle market, and we will hopefully also witness the first NFC blade projects.”

Challenging raw material suppliers to do better

The manufacturing stage of the Green Nacelle progressed rapidly and without issue, the Sicomin epoxy products and Bcomp’s ampliTex™ natural-fibre technical products performed as expected and also met all structural requirements defined by the client and composite engineering team. When asked what more could be achieved in material technology, Deimann added, “Already the product we made is ap­proximately 80% based on natural materials. The sustainability can be further improved by increasing the bio-content of the resin system, and this is something we would be more than happy to evaluate.”

Sicomin are indeed up for the challenge as Philippe Marcovich, President, Sicomin, comments: “We work continuously on R&D developments to enhance our innovative chemistries. Today, we have the highest bio-content on the market and can supply the industrial volumes that the wind energy market would need. Moving forward, we are constantly looking at new formulations and developments that will let us provide our customers with even higher levels of sustain­ability in the future.”

Greenboats, Sicomin and Bcomp look forward to further feedback from the DOT test programme as the project moves into the next phase.

This article has been published in the JEC Composites Magazine N°143.