The successful output of MEGAWIND project involves newly introduced composite material tower for wind turbines, a 30m split blade suitable for installation on MegaWatt class wind turbines operating in high wind speed, complex terrain sites and a gearbox specially designed for a wind turbine, giving extra emphasis on the compact design and a reliable operation. Design and manufacturing assessment has been conducted on the wind turbine components.

Composite tower: The design approach to such a composite structure is based on the critical interaction between the design and the manufacturing process, therefore, the design team and the construction and material production engineering team were continuously in close collaboration. The tower design and its construction procedure addressed key issues relating to the erection of large wind turbines in isolated locations such as logistics of construction and long term maintenance. The group elaborated the conceptual design of the main structural elements of the tower and provided a design for the tower, based on the use of fibre-reinforced composites. Numerical simulations were used for assisting in the verification of the dynamic and structural performance of the tower. In addition to this, large-scale structural tests on representative subassemblies of the tower design were carried out before the approval of the final construction. Eventually, extra emphasis was given on the optimisation of the composite lamination sub-element joining as well as the manufacturing process. At the end, a composite material tower of 40 m height was manufactured. The innovative tower design and construction were evaluated by performing extensive full-scale static and dynamic testing on the prototype.

Split blades: Aerodynamic blade design was performed for maximizing the annual energy capture (AEC) of the rotor at a typical high wind speed site. AEC was evaluated using enhanced blade element theory. Design variables were the blade chord and twist distribution and the profile shapes of the blade sections. An extended database of such profiles was available to the partners, including the geometry and the lift-drag polars of almost 200 airfoils. A genetic-algorithm-based optimiser was employed, allowing for discrete optimisation (search in the profile database to select the best suited for a specific blade section). Constraints were put on the maximum blade loading and geometry (blade area, maximum thickness of the blade sections etc.). From the structural point of view the blade is made mainly of Glass/polyester composite, although carbon fabrics were considered during the design phase. Material mechanical properties used for the design calculations were already available from manufacturer’s database. However, additional tests on carbon/polyester and hybrid glass-carbon/polyester laminated coupons were performed to characterise its strength and stiffness properties. Special emphasis was given in the conceptual and structural design of joining elements. The validation of accurate fatigue life estimation for the joining techniques was backed-up through extensive laboratory sub-component testing. The design was performed according to IEC 61400-1 for a class I blade. The 30 m long split blade prototype was manufactured and thoroughly tested in a full-scale testing laboratory.

Transmission system: For the development of a high reliability, low cost, low weight and low noise emission geared drive system for large W/Ts subjected to high wind turbulence and complex wind inflow conditions, the conceptual design of novel mechanical drive systems from rotor to generator was developed and alternative gearbox configurations were investigated. The dynamic performance of these drives and control systems were evaluated numerically. The most appropriate was selected and the parameters of the mechanical drive and of the control systems were optimised to give minimum dynamic overload. At the final stage the design of the mechanical drive e.g. shafts, bearings, couplings, mountings was performed. In order to evaluate the newly designed gearbox, a drive train of similar concept to the proposed one was installed on a commercial 1.3MW WT, operating on a high wind speed complex terrain site. After a short commissioning period of the WT with the refitted gearbox, extensive field-testing was performed according to the relevant IEC standard. In addition, a comprehensive instrumentation system to monitor dynamic shaft torques, triaxial rotor bearing loads, gearcase vibrations etc. was installed for the first time inside a WT gearbox. Measurements were carried out focusing especially at the drive train and the intensively instrumented gearbox.

Design assessment & feedback, standardisation and industrial implementation: Assessment of the design of the tower, the blade and the gearbox were performed on the basis of the acquired measurement data and input was provided to the design groups and the construction companies for the refinement of the design and of the manufacturing processes and techniques. Conclusions were drawn and recommendations were compiled on the application of the new technologies for the use of wind farm developers and decision-makers. Technical information will be made available also to the certification and standardization authorities in order to facilitate the certification process of the W/Ts of this construction.