European renewable energy targets continue to fuel the wind turbine industry, with the development of the offshore market pushing the demand for even larger turbines. Some of the designs currently in use have rotor diameters in excess of 120 metres, and the blades are required to perform efficiently under extremely turbulent conditions.
Rotor blades can account for 20-25% of the overall cost of a wind turbine, so it is essential that the blades are efficient and provide long service with little maintenance, to ensure their cost-effectiveness. Manufacturers are constantly developing the production process as new methods and technology are integrated. The move towards mass production to meet the demand of the growing offshore market, and the opportunity to manufacture close to site, offers the potential to reduce the cost of rotor blades significantly.
Rotor blade design concepts
Aerodynamics is crucial in rotor blade design; in the past blades have been designed on the basis of aviation airfoils, but these airfoils are intended for plane wings which are placed under entirely different wind flow conditions to turbine blades (1). Most blade manufacturers use their own customised design for turbine blade airfoils, and are continually developing the technology behind them.
The aerodynamic design of a blade dictates its width, thickness and twist. And the key challenge to manufacturers is to find a compromise between air flow and blade strength to optimise performance and efficiency. In pure terms of aerodynamics, the perfect blade design would see a blade which is thick, wide and very long. In reality, this is not viable as the blade would put far too much strain on the turbine, and could strike the tower upon rotation. The strongest type of blade would be one of a circular structure, but this is equally implausible as such a blade would have minimal lift, and would not be suitable for producing energy from wind power. These extreme examples indicate why it is so important to find the best balance between air flow and strength in blade manufacture to improve efficiency.
One of the world’s leading blade manufacturers, LM Wind Power, have sold over 130,000 blades equivalent to a capacity of 43 GW; and more than one in three wind turbines in the world is fitted with their blades (1). They use several innovative design concepts to improve performance, and are at the forefront of glass fibre development to produce lighter more efficient blades.
One unique feature in the design of LM blades is the pre-bending process, which means the blades flex towards the wind once they are mounted and are not subject to loading (2). Clearance of the tower is essential in blade design, and the tip to tower distance is critical. Interested in reading more about rotor blade design concepts? Find out more here.
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