Composites Manufacturing for Airborne Wind Energy

Joep Breuer

Project Manager Airborne Technology Centre

Laan van Ypenburg 70–78 2497GN Den Haag

The Netherlands j.breuer@airborne.nl www.airborne-technologycentre.com

Composites Manufacturing for Airborne Wind Energy

Airborne Technology Centre One of the requirements of the airborne part of an

Air-borne Wind Energy Plant, the kite, is low weight. On the one hand to keep the mass inertia of the moving system low and on the other hand making it easier to keep the kite airborne in very low wind conditions. Another is of course low costs.

Using High-tech materials like fibre reinforced plastics, commonly known as composites, is a way to reduce weight. As a guideline; composite structures can be about 30% lighter than comparable metallic structures due to their reduced density.

In general there a number of ways to manufacture com-posite products dependant on the base material. Pre-pregs or pre-impregnated fibres are currently the stan-dard in the aerospace industry to produce high quality parts. But the material is expensive and the technology needs expensive equipment.

Dry fibres are used for infusion techniques. Dry fibres are placed in a single or double sided mould and the fi-bres are infused with resin using a pressure difference be-tween the in- and outlet. This technique is widely used in the manufacturing of ship hull and wind turbine blades. Infusion gives more flexibility both in material choice as in type of infusion technique depending on the necessary quality of the final product.

The third material is the use of thermoplastics as ma-trix/resin for the fibres. Thermoplastics can be formed and reformed again through the input of heat. Although not yet widely used for aerospace parts it has great po-tential due to its impact toughness, and the possibility to weld and recycle.

Most AWE rigid kite and aircraft designs tend towards a carbon fibre/epoxy design. But highly loaded parts are mostly made of metals. Changing to a composite struc-ture will not only result in a weight decrease on part level but also reduce weight/cost in the complete design. A suitable production method of these highly loaded com-posite parts is closed mould RTM infusion. This pro-cess is able to produce composite parts with high toler-ances and big differences in wall thickness. In a AWE kite the tether/kite interface could be such part but also the tether/pod interface for soft kites.

The production of composites is very labour intensive, for this reason, automation of the production of compos-ites has become such an important topic. There is a big push from the automotive sector to automate production of composite parts. The aerospace industry is also look-ing in to automation not only due to production costs but also to ensure a more consistent quality and easier trace-ability reducing costs in inspection and quality control. In AWE quality will be extra importance due to the ex-pected fatigue effects of the continuous load cycles and safety aspects which will be more stringent than for nor-mal wind turbines.

Several trends in the aerospace composite manufactur-ing industry seem suitable for Airborne Wind Energy ap-plications to make lightweight and low cost, but high quality, parts in large quantities (compared to aerospace production rates). Automation is the main focus in combi-nation with dedicated infusion techniques and in the fu-ture the use of thermoplastic materials.