Innovation has been driving the wind power market and its large, medium and small-scale versions. With the growing demand and awareness towards renewable energy sources, various innovative approaches have been developed to use the energy generated from renewable resources. Wind turbines have continually and considerably improved from those first developed in the 1980s and 1990s. With innovations, wind turbines have become more cost-effective, more reliable and capable of much more power production. Today, turbines are considerably larger with greater power generation capacity, which can go up to 12 MW.
Turbines make use of wind energy with their propeller-like blades, which act much like an airplane wing. The blades are the motor in a wind turbine. They extract all the energy from the wind. When the wind blows, a pocket of low-pressure air forms on one side of the blade. The low-pressure air pocket pulls the blade towards it, causing the rotor to turn. Blades are an important part of a wind turbine. They used to be very bulky in the beginning (Figure 1a). However, over time, blades have been modified with innovations, not only in design but also in material, science and technology to make them lightweight, economical, and free of noise, friction and corrosion, producing more angular speed for the same torque with a low rotational inertia (Figure 1b).
Wind turbine blades should be light as they are more efficient when they are lighter. It makes the wind turbines easier to assemble and disassemble as well as easier to turn, thus enhancing their performance. Having fewer blades reduces the drag. The two-bladed turbines wobble when they turn to face the wind. With the use of three blades in wind turbines, the angular momentum stays constant because when one blade is up, the other two are pointing at an angle, so the turbine can rotate smoothly in the wind.
Although the basic blade design has not changed, designers and manufacturers have continued working on developing the world’s smallest and largest turbine blades. Finding the perfect balance between wind turbine blade design and their aerodynamics presents the greatest design challenge of wind turbine blade length. The aerodynamic properties are crucial in determining how well a wind turbine blade can extract energy from the wind and efficiently produce wind power.
Tried and tested building blocks are the basis for all blade development projects. Creating new and reliable wind turbine blade designs by developing and testing the best materials for turbine blades are part of the current research. Proven wind turbine blade designs are helping with efficient and cost-effective wind power generation. Optimised blade solutions are setting new standards for the cost of energy, and the use of flexible building blocks is helping in finding the optimal fit for the turbine.
A detailed review of the current state of the art for wind turbine blade design covers parameters such as maximum efficiency, propulsion, practical efficiency, blade design, and blade loads. The review should provide a complete picture of wind turbine blade design and highlight the dominance of modern turbines with almost exclusive use of horizontal axis rotors. The use of aerodynamic design principles in modern wind turbine blades is proving very beneficial for making efficient blades with respect to blade plan shape/quantity, aerofoil selection and optimal attack angles. Detailed studies of design loads on wind turbine blades take into account aerodynamic, gravitational, centrifugal, gyroscopic and operational conditions.
New technology is helping redefine wind turbine blades. These blades are being fabricated with composite materials such as fibre-reinforced polymer composites, including carbon, glass and natural fibre. These materials often comprise up to 50 per cent of the cost of a manufactured wind turbine blade. Materials being considered in the wind turbine blade market include resins of glass fibre-reinforced polyester, glass fibre-reinforced epoxy, and carbon fibre-reinforced epoxy. A combination of glass fibre and resin matrix results in composites that are strong, lightweight, corrosion-resistant, and dimensionally stable. Based on modular technology featuring modular aerodynamics, modular structure and modular manufacturing, tooling can deliver customised blades in various lengths and structures for different capacity wind turbines and extend their life cycles to perform under varying conditions of wind, temperature and humidity. In the wind turbine blade manufacturing process, blades have to be tested to their limits, and continuously improved with the latest, innovative wind turbine blade materials.
Theoretically, an infinite number of blades with zero width is the most efficient solution. However, various scientific and engineering considerations always lead to the logical compromise of having a wind turbine with only a few blades. Component costs that are affected by blade count are primarily the reason for this. It is well known that the lower the number of blades, the lower will be the material and manufacturing costs. In addition, with a lower number of blades, the rotational speed can be higher. Further, thin blades are required to avoid interference with the tower limit. Fewer blades with higher rotational speeds also reduce peak torques in the drivetrain, thus resulting in lower gearbox and generator costs. In addition to all these technicalities, aesthetics can be considered a factor as some people find three-bladed rotors to be more pleasing than one- or two-bladed rotors.
To reduce the cost of energy conversion and optimise energy production, researchers from various research organisations, companies and institutions are working together to design not only innovative wind turbines but also blades. With larger blades, more kinetic energy from the wind can be harnessed and used to generate electricity. However, transportation and manufacturing costs will rise in response to increased material mass and demand.
Researchers and engineers are trying to find ways to decrease the stiffness of the blades and for the turbine to hold more upcoming wind, regardless of the speed. Changing the shape of traditional turbine blades has resulted in the development of lighter blades. This approach allows for aeroelastic stability, but at the cost of increased complexity for manufacturing and control. Researchers are currently working on designing lighter blades and optimising spar cap placements on the blades without increasing thickness. This would minimise blade mass and increase strength.
As the technology matures, advancements are on the horizon to extend wind project lifespan while simultaneously lowering operational costs. Some of the main areas of innovation in wind turbine blades are:
- Longer and lighter rotor blades, with some reaching 95 metres in length.
- Blades with curved tips, designed to take maximum advantage of all wind speeds.
- Blades that are able to withstand the stress of high-altitude wind and taller towers.