Wind turbines are costly, and the blades are the most expensive parts to manufacture. Since the blades are the working parts of a turbine, they require the most attention to detail. Engineers have spent years perfecting the shape of the blade, from the aerofoil design to the twists and turns which maximize efficiency. But what are the blades actually made of? As it turns out, it’s not what you think. At first glance, many would expect the blades to be made of aluminum, just like an airplane wing. But the blades of a wind turbine are subject to very different conditions than those of an aircraft. Therefore, the blades are manufactured using a composite mix of glass, carbon fiber, and plastic. It’s a unique material that gives the blades the strength and durability to do its job.
Structure of a Turbine Blade
There are many different types of wind turbine, but the most common – horizontal axis wind turbines, or HAWTs – have three blades shaped like aerofoils, similar to the shape of the wing on an airplane. Because of this, the cross-section isn’t entirely tubular; but instead has more of an oblong shape. The bottom of the blade deflects oncoming air, creating an area of high pressure. The top of the blade then cuts through the air as it’s pushed by the lift from the oncoming wind. This causes the rotor to spin, feeding kinetic energy to the generator in the nacelle which converts that energy to electricity.
While in motion, the blades of a turbine experience different wind speeds at different parts of the blade. To account for this, engineers incorporate slight twists along the leading edge of the blade. This is to ensure that the blade captures the maximum amount of wind energy possible.
While they may look like one giant piece, turbine blades are actually like a shell. They are composed of two large halves pressed together to form the whole blade. The two halves are held together using adhesive joints and an internal framework usually consisting of carbon fiber.
What are the blades made of?
The blades of a wind turbine are made of several layers of glass or carbon fiber infused with a liquid plastic resin. This creates a composite material that is strong, durable, and lightweight, giving the wind turbine a long lifespan. It also has a low density. The material allows the blades to do their job effortlessly while taking on heavy loads and stresses. The combination of glass and plastic creates a material that can bend, warp, and withstand wide temperature fluctuations and variable wind speeds.
These materials also give the blades a low rotational inertia. Whereas other materials, like metals, are heavy and take time to accelerate, the composite material can accelerate quickly when wind speeds pick up. This means the blades retain more constant speeds, which leads to less overall stress on the turbine.
The ratio of materials varies greatly according to the size of the turbine and its location. Turbines in areas with high wind speeds are going to be built much differently than turbines in low-wind speed areas. Furthermore, larger turbines are going to be built with stiffer blades. As the blades get longer, they are more likely to flex at the tips, so the ratio of materials must be adjusted to ensure that the blades don’t collide with the tower.
How are Wind Turbine Blades Made?
While we may imagine wind turbine blades to be manufactured in a highly precise setting, the reality is quite the opposite. While the shape of the blade is made to specific standards, the actual crafting of the blade is made in a qualitative manner. That means that much is left to the discretion of the engineers and workers on site. Still, turbine manufacturers build their blades to rigorous standards to ensure maximum efficiency for energy production, as well as the safety of the workers both in the factory and on the field.
Check out this video to watch the process from start to finish.
Step 1: Layering the Fabrics
Wind turbine blades are made of composite materials. Composite materials are made of several different materials combined to achieve vastly different properties from those of the individual materials. In the case of wind turbine blades, the materials used are several different types of glass, aramid, and carbon fiber fabrics which, whilst ideal for their purpose, are difficult to dispose of or reuse in future. The ratio may differ depending on the manufacturer or size of the turbine.
Blade manufacturers may use up to ten layers of fabric. Many of these layers are axial, meaning the fibers are arranged at an angle. The first fiber is a peel ply, or protective cover, followed by up to five layers of glass fabric. Some fabrics are biaxial, with crisscrossing fibers, while others are woven in a unidirectional pattern. A second peel ply is placed over the layers of fabrics.
Step 2: Molding the Blades
These fabrics are then placed in molds to prepare them for the liquid plastic molding phase. Each mold is shaped like one half of the turbine blade and will each make up a face of the blade. More fabric is placed on top to prepare for molding. A perforated release foil and a distribution medium are used to help the plastic resin properly flow and absorb into the fabric.
The entire mold is then wrapped in plastic and vacuum sealed. Once fully vacuumed, a plastic epoxy resin is pumped into the mold. The resin is then allowed to flow throughout the mold and infuse with the glass and carbon fibers. Once fully infused, the mold is heated to harden the composite material. When the mold cures, it takes on a solid shape.
Step 3: Assembly & Lamination
Now that the fabrics are infused with plastic resin, the two halves of the mold are ready to be assembled. High-strength adhesives are used to press the blade together. Then, depending on the manufacturer, they are locked together either by a series of joints and/or an internal framework of carbon fiber girders. The excess adhesive is removed using a handsaw.
The outer surface of the blade is then laminated with a thermoplastic resin. This gives the blade a smooth surface and a resistance to elemental exposure. Once complete, the blade goes through a process called machining. Metal rods are placed at the inside edge of the blade, where it will meet the hub. These rods will be used to fit the blade onto the rotor. Finally, the blades are made white, to match the white of the rest of the turbine.
Step 4: Stress Testing
Once assembled, the blade goes through numerous tests and inspections. Engineers inspect the weak points of the blade for faults or cracks. The blades are then put through stress tests, where they are subject to a range of conditions they may experience while in use. This includes extreme temperatures, strong winds, and unusual movements.
The main issues engineers search for are microcracks. These are tiny fractures in the blade’s surface that may expand and eventually lead to structural failure. Once the blade passes the tests, it is ready to be shipped off.
Future of Wind Turbines: Carbon Nanotubes
Researchers are experimenting with using carbon nanotubes in the construction of wind turbine blades. Carbon nanotubes are incredibly strong, given their weight. The addition of these nanotubes will help strengthen the blades and greatly reduce the possibility of fractures while still allowing for some flexibility.
The idea is to use the nanotubes to reinforce the composite material in the blades. They can either be grown into the glass fabrics or added to the liquid resin. Some researchers say that the addition of conductive carbon fibers can help give the blades a resistance to lightning and can mitigate any potential structural damage arising from a lightning strike.
Wind turbine blades are a unique engineering feat. Although they share many similarities with airplane wings, their functions are completely different, and so is the manufacturing process. Whereas aircraft are usually made of aluminum, the blades of a turbine require a composite material made of glass, carbon fiber, and plastic to achieve the perfect tensile strength for the job. Designs are constantly being improved upon, and no manufacturer has yet to find the perfect design. Other designs for wind turbines even call for a total lack of blades. Wind energy is still in its early phases. As time goes on, we can expect to see different materials develop, which enhance the efficiency of the blades and provide more energy per turbine.
Frequently Asked Questions
The blades of a wind turbine are made of a composite material composed of glass fabric and carbon fiber infused with a liquid plastic resin. This material offers the best strength to weight ratio and can withstand the extreme pressures that come with constant rotation. The ratio of material changes depending on the size of the turbine and its environment.
Early wind turbine blades were made with aluminum. As time went on, engineers found that aluminum was too heavy and instead began using other materials like carbon fiber, glass fabric, and plastic.
The blades begin with two molds, each shaped like one half of the blade. The layers of glass fabric and carbon fiber are laid out on the mold, then vacuum sealed in a plastic wrap. Liquid plastic resin is then pumped into the vacuum-sealed wrap until it fully absorbs into the fabric. The material is then allowed to cure. Once hardened, the two halves are then pressed together with adhesive joints, and a plastic laminate coating is applied to the surface. The blades are then tested for structural integrity.
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