The wind energy market is experiencing rapid growth worldwide and has doubled in size every 3 years for the past 30 years. It is expected to have generated 331 TWh in 2010 alone, amounting to 1.6% of global energy consumption. This expansion requires new manufacturing plant including facilities for large composite blades. Applied Market Information Ltd. (AMI) organised a global networking conference on Wind Turbine Blade Manufacture in Germany in December 2010 to bring together energy companies, wind industry players and the composites supply chain, with top blade manufacturers and researchers reviewing the latest innovations and the issues.
The process of blade manufacture is very labour-intensive involving hand lay-up: automation is being developed and quality control from production stages to installation is key to wind farm success. The cost of energy production is lower with larger turbines due to lower installation costs, which is driving up the size of blades. It is even more of a factor offshore where turbines and blades are being designed to need less servicing, because of the difficulties of access. The blades comprise a root area providing the connection to the hub, and an aerodynamic area. The structure is supported by the load-bearing spars. The sequence in blade manufacturing is material preparation, tool preparation, component moulding, assembly and finishing. Manufacturing process factors that can affect blade quality include fibre misalignment and waviness, dry spots (no resin), and voids in bonding.
LM Wind Power is a global leader in blade manufacturing: the company has produced 140,000 blades since 1978 and has 13 production facilities. It is operating in Asia, Europe and the Americas and estimates that more than 1 in 3 wind turbines use its blades. In line with other parts of this industry, it offers to service blades and turbines through its logistics division. In-house design and testing facilities allow LM Wind Power to adjust its blades for different operating conditions. Blade service life is determined by factors such as fracture mechanics and wind loading, because composites degrade when loaded. Surface damage occurs due to erosion and lightning strikes: lightning is a problem in composite structures that needs to be managed.
Vestas Wind Systems has installed more than 41,000 wind turbines in 65 countries. It has its own blade production facilities and research. The company is prioritising quality control aiming for Six Sigma systems, which means 3.4 defects per million opportunities – the process is gradual and the target for 2010 was 5 Sigma. One case study on blades examined areas that might cause problems, like damage to the core foam from an extended cure cycle due to trapping of heat inside the laminate: in this instance the designer can check the exotherm before starting production. In a two-mould factory this work can increase productivity by 9%, equivalent to 66 more blades per year. Quality control is the focus of the company Vesper, because current measures tend to be manual and irregular. The company is using a non-contact laser-based scanner to inspect blades, taking around 12 hours, and detecting shape variation.
