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Low cost offshore wind turbine R||D with 3D printing, polymer fibers to create energy-producing textiles

Low cost offshore wind turbine R||D with 3D printing, polymer fibers to create energy-producing textiles

The trend toward ever larger offshore wind farms continues unabated. As offshore wind turbines are becoming larger- and transportation, installation, disassembly and disposal of their gigantic rotor blades are presenting operators with new challenges. Wind turbines with rotor blades measuring up to 80 meters in length and a rotor diameter of over 160 meters are designed to maximize energy yields. Since the length of the blades is limited by their weight, it is essential to develop lightweight systems with high material strength. The lower weight makes the wind turbines easier to assemble and disassemble, and also improves their stability at sea.

Researchers have partnered with industry experts to develop highly durable thermoplastic foams and composites that make the blades lighter and recyclable. Thanks to their special properties, the new materials are also suitable for other lightweight structures, for instance in the automotive sector. In the EU's WALiD (Wind Blade Using Cost-Effective Advanced Lightweight Design) project, scientists at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal are working closely with ten industry and research partners on the lightweight design of rotor blades. By improving the design and materials used, they hope to reduce the weight of the blades and thus increase their service life.

These days, rotor blades for wind turbines are largely made by hand from thermosetting resin systems. These, however, don't permit melting, and they aren't suitable for material recycling. At best, granulated thermoset plastic waste is recycled as filler in simple applications. For the outer shell of the rotor blade, as well as for segments of the inner supporting structure, the project partners use sandwich materials made from thermoplastic foams and fiber-reinforced plastics. In general, carbon-fiber-reinforced thermoplastics are used for the areas of the rotor blade that bear the greatest load, while glass fibers reinforce the less stressed areas. For the sandwich core, Rapp and his team are developing thermoplastic foams that are bonded with cover layers made of fiber-reinforced thermoplastics in sandwich design. This combination improves the mechanical strength, efficiency, durability and longevity of the rotor blade.

3D printing of a mold for the wind turbine blades can lead to cost-savings within the product development cycle, and the technology also makes it easier, and cheaper, to add more functionality into components, the Offshore Wind Infrastructure Application Lab (OWI-Lab) reports. Wind turbine blades produced for research purposes can easily be more than 12 meters in length, which is to date too long to be printed in one run. This is why the Advanced Manufacturing Office (AMO), part of the US Department of Energy, together with a number partners, started the research to the use of 3D printed sections of almost 2 meters which can be used to make large molds to produce a full blade. Projects like this one require larger 3D printing capacity and the AMO team managed to locate it at the Manufacturing Demonstration Facility (MDF) at the Oak Ridge National Laboratory, Tennessee, USA, which houses a so called 'Big Area Additive Manufacturing' (BAAM) 3D printer. The equipment tends to be 500 to 1000 times faster than most other industrial 3D printers and has a building capacity that is many times greater. Although this type of 3D printer is not quite capable of working at the actual dimensions required for a full blade, it does provide a realistic overview on how to take on such projects in practice, according top OWI-Lab. First, a CAD model of the blade was designed: in principle a typical blade design from which a mold was made and cut into 3D printable sections, complete with assembly holes and discharge ducts for the hot air. Sections measuring almost two meters were then 3D-printed. These sections were then given a glass fiber laminated layer and smoothed off. Each mold segment was placed in a frame with a hot air blower, temperature control and thermocouples. The innovative technology using hot air saved energy and eliminated the labor-intensive step of manually installing the heater wires, which are traditionally embedded into the mold., OWI-Lab said. Moreover, the air blowers can be reused for new molds in the future. Once assembled, the gigantic 3D printed mold had an extremely uniform surface, perfect for manufacturing wind turbine blades or tidal generator blades at a lower cost when using the traditional production methods, according to OWI-Lab. Various blades were produced as demonstrator during this research project using the 3D printed mold.

A team of researchers has developed a textile capable of harnessing energy from both sunlight and wind. The team developed a fabrication strategy that merged two different lightweight, low-cost polymer fibers to create energy-producing textiles. The first component of the textile is a microcable solar cell, able to gather power from ambient sunlight. The second is a nanogenerator capable of converting mechanical energy into electricity. The photovoltaic portion of the textile was composed of a copper-coated polymer fiber that was then further coated with concentric layers of manganese, zinc-oxide/dye, and copper iodide–the zinc oxide is a photovoltaic material, while the copper helps harvest the charges. These solar-cell microcables were then woven together with a copper wire. The second energy-generating material was based on triboelectric generation, where certain materials generate electricity when they experience friction. For their textile, the researchers used copper-coated polytetrafluoroethylene strips woven together with a copper wire. The solar-cell microcables and triboelectric nanogenerator stripes were woven together with yet more copper wire. This was done using an industrial weaving machine, so no specialized equipment is needed. The end result was a wearable textile that exhibited an interlaced, single-layer structure with a thickness of 320µm.

The researchers demonstrated the ease of the weaving process by fabricating colorful textiles with arbitrary size and weaving patterns. They also integrated the textile into many common fabric items, such as cloth, curtains, and tents. The team then optimized the properties of individual components, starting with the photovoltaic textile. Here, the electrical connection among the solar cell microcables strongly impacts the power output. By altering the number of strings and the connections they form, the researchers demonstrated the ability to tune the electrical output of the photovoltaic textile to fulfill various power delivery requirements. They also found that the weaving patterns impacted the ambient solar energy conversion and determined that the plain-weave structure generated the highest current density.

Under ambient sunlight, and in the presence of wind blowing or human motion, the textile swatch was able to charge a small commercial capacitor up to 2V in one minute. The textile could continuously power an electric watch, charge a cell phone, and even drive water-splitting reactions, releasing hydrogen. Due to the breathability, flexibility, and robustness of the textile, it is a prime candidate for wearable electronics. Using a textile swatch of 4×5cm, the team evaluated the textile's properties on a person who was walking under sunlight (80 mW/cm2 intensity). The textile was highly deformable and responded well to human motion. They found that the fabric was able to deliver an output power of 0.5 mW even when elements in the circuit itself drew significant amounts of power (with loading resistances ranging from 10 K☊ to 10 M☊). Overall, the fabric doesn't generate a lot of electricity. But it has the advantage of being able to generate electricity where it may be needed‐there's something to be said for charging your phone while you walk or powering up your GPS by plugging it into your tent.

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