Wind blade composites market grows as offshore wind energy advances

Design is the key issue in blade scale up. Dassault Systemes Deutschland supplies composite simulation software to the wind industry covering aerodynamics, structural analysis, design and manufacturing planning. Quality control can offer big opportunities for cost savings, in one aerospace project with EADS Composites Atlantic the scrap rate was reduced from 13% to zero.

Vestas has 30 years of experience in wind turbine development and has 44,000 installed in 66 countries on 6 continents. The company’s V112 3MW turbine is established for operating in low and medium onshore winds. The company manufactures blades at 8 sites worldwide: Windsor and Brighton in Colorado, USA; Lem, Denmark; Daimiel, Spain; Taranto, Italy; Lauchhammer, Germany; and Hohhot and Tianjin, China.

Vestas blades were initially manufactured as polyester shells and spars: this changed in 1991 to an epoxy spar and in 2002 the company used a carbon fibre-reinforced spar for load bearing. This allowed it to add 5 metres to the length of the blade without increasing the weight. Frank Weise, the Vice President of Vestas Blades Deutschland, described the slender V112 blades including the wider root diameter to reduce blade bearing wear, integrated lightning receptors and grounding cable, and profile design for low noise level.

The planned lifespan is 20 years. Weise’s manufacturing background began in Japan and he is studying the whole production process and introducing standard operating methods with controls at each step to ensure consistent, high blade quality. This is a key precursor to instigating automation, which is still proving difficult in the wind composites industry.

One of the certification bodies for wind blade manufacturing sites is Germanischer Lloyd (GL) and some wind farm authorities and insurers expect this standard from suppliers. The standard covers facilities, materials, processes, and personnel qualifications.

For example, the workshop is expected to keep temperature and humidity within limits and the laminating resin is specified as having good wetting and impregnation, resistance to ageing, cure between 16C and 30C with a maximum of 12% filler by weight. At the Wind Turbine Blade Manufacture 2011 conference questions were asked about the compatibility with IEC guidelines and the rationale for the GL requirements.

The Fraunhofer IWES conducts rotor blade testing, which can take a year for fatigue tests. It is developing facilities for up to 80 metre blades. At the end of 2010 biaxial testing was implemented, for example with vertical loading in blade eigenfrequency plus horizontal quasi-static loading. Movement of the blade was monitored at different radii and the tip at different load levels. The Materials Engineering Research Laboratory (MERL) has looked at the causes and modes of delamination in composites in order to predict fatigue life. This can then be factored into the design process.

Euros Entwicklungsgesellschaft Fuer Windkraftanlagen designs blades in Germany and has two manufacturing sites in Poland at Ustron and at Zory-Warszowice. The company carries out its own testing programme, for example on coupons to determine material properties, on samples to see the performance of complex structures and on full scale blades to exclude size effects on smaller samples. Mass content measurements can be misleading if the stitching yarn and the sizing covering the glass fibre are not taken into account as these will decompose during calcination of a specimen and this may affect the calculation of void content.