Wind turbine blades have a difficult job with some very harsh working conditions on earth. They must be stiff and strong enough to withstand the elements day in and day out. Yet, they also need to be light enough not to strain other components on the wind turbine and slow down its rotation. The design life of a wind turbine is around 20 years, and the blades do wear out sometimes.
Wind turbines are intentionally erected in some of the harshest locations. By design, wind turbine blades are exposed to extreme forces from the wind and from their immense weight. However, field failures are costly and difficult to fix because wind turbines are so tall and the blades are extremely long and heavy.
Numerous stressors can cause wear and tear on wind turbine blades, decrease energy production, and even break on very rare occasions. Fatigue damage from wind, lightning strikes, blade edge erosion, and icing are some of the primary reasons wind turbine blades can become damaged and wear out.
Yet, wind turbine blades must be extremely effective in helping the turbine convert kinetic energy into mechanical energy. They are designed to decelerate or slow down the wind as it passes by and works similarly to an airplane wing. In fact, the blades are curved to generate lift, causing the wind energy turbine to spin.
How do wind turbine blades wear out?
Fatigue damage is one way that blades can get worn out and is often located where the blades meet the hub. Wind turbines are under a tremendous amount of stress, largely from the wind, which can cause fatigue damage.
As stated in A Comprehensive Analysis of Wind Turbine Blade Damage, “All of the factors with an unfavourable influence on a material’s fatigue strength are present in this area: stress concentration, bolt holes, built-in stresses, offsets, changes of section and application of different materials. Fatigue damage in the joining zone of the blade with the root appears initially as tiny cracks, which tend to become more severe over time.”
Turbine blades experience a lot of repetitive loads, day in and day out. This can eventually create fatigue damage. Turbulent wind conditions can be especially difficult for turbine blades, and eventually lead to localized cracks forming in the blades.
One way to help avoid fatigue damage is through proper wind turbine siting.
Adequate spacing and locating wind turbines on terrain that won’t cause excessive fluctuating aerodynamic loading and turbulence intensity are helpful.
How does gravity wear out wind turbine blades?
Wind turbine blades experience a variety of fatigue loads that can cause structural damage. bending from the wind itself and from their own weight. When blades point to 3 o’clock, gravity bends the blade down toward the earth. Then when it reaches the 9 o’clock position, its gravity bends the blade in the other direction.
To help boost the lifespan of wind turbine blades, it’s critical for them to be very stiff to prevent the blades from breaking. Otherwise, the forces from gravity and the wind become too much for the wind turbine blade and its fatigue strength is exhausted.
Can lightning damage wind turbine blades?
Unfortunately, yes and it isn’t entirely uncommon. Lightning typically strikes near the tip of the blades, where the material is thinnest, so that is where damage is most common. Certainly, some project sites are more susceptible to lightning strikes than others due to climatic conditions.
Lightning can cause cracks to form in the blades. This can cause two different types of damage to the blade, delamination and debonding, which are often present at the tip or leading edge. Delamination and debonding can cause structural degradation of the resin due to heating and separation of the upper and lower shells of the blade. According to research, delamination is about three times more common than debonding in wind turbine blades.
Because the wind turbine blades are located at the top of the wind turbine, they are the most important part of the turbine to protect from lightning. These tactics include driving the lightning to a desired point on the wind turbine and grounding to cause the lightning current to pass through the wind turbine and safely into the ground. In addition, lightning protection can be installed on the wind turbine blades, such as air termination systems and resistive tapes.
Although lightning protection systems can be helpful in preventing damage, they certainly don’t guarantee that a lightning strike won’t damage the turbine blades.
How does icing wear out wind turbine blades?
In extreme cases, wind turbine icing can cause a threat to the structural health of a wind turbine and create a safety hazard. In some cases, ice formation can affect the shape of the wind turbine blade, impacting its aerodynamic efficiency.
Unfortunately, icing can create excessive vibration and imbalances in the blades, which causes wear and tear on other wind turbine components, like the gearbox. In some cases, asymmetrical icing can create fatigue loads because of the imbalances the weight and shape of the ice create.
Wind farm operators have a couple of approaches they use to avoid the negative impacts of icing. De-icing approaches help remove ice from the blade after it forms and can help reduce the duration of an icing event. For example, hot air deicing heats the air inside of the wind turbine blade causing the ice or snow on the outside of the blade to melt. Although this approach does use electricity, it can boost overall energy production if it prevents downtime from winter icing events. Unfortunately, the heat from such de-icing methods has the potential to damage the turbine blades.
Anti-icing approaches help prevent or delay the formation of ice on wind turbine blades. Often, this involves coatings that prevent water from accumulating on the blade.
How does the shape of wind turbine blades impact durability?
Two of the main stressors on wind turbines are from gravity and from the wind itself. Wind turbine blades have an airfoil shape, which is a specific wing shape. They are flat on the bottom and curved on the top. This design causes high and low-pressure areas on the blades, creating lift.
In fact, the lift force of the turbine blade depends on the shape of the blade because it impacts the lift coefficient. In addition to fatigue damage, leading-edge erosion is a common way that wind turbine blades wear out.
Airbourne particles, such as hail, dust, sand, and sea-spray increase the surface roughness of the turbine blade. Unfortunately, leading-edge erosion can create more drag, reducing wind power generation. In extreme cases, it can impact the blade’s structural integrity.
Yet, to optimize its aerodynamic design, wind turbine blades must also be thin. If the blades are too thick, there would be a lot more drag. Manufacturing slender blades also help reduce the weight of the blades but this creates a balancing act. Wind turbine blades must be relatively thin and lightweight, yet also create enough lift to harness wind power and be highly durable.
Common ways to mitigate blade erosion are to apply anti-corrosion protective tapes or coatings on the leading edge of the blade. For similar reasons, coatings are also widely used on helicopter rotor blades.
How big are utility-scale wind turbine blades?
Getting a sense of the size and weight of wind turbine blades helps explain why they wear out. A typical 1.5 MW wind turbine has blades that are 34 to 38 meters (110 to 124 feet) long and weigh about 5,216 kilograms (11,500 pounds). And these turbines cost about €93,000 to €116,000 ($100,000 to $125,000). But a 3 MW wind turbine is even more immense, with blades that are 47 meters (155 feet) in length and weighing 12,474 kilograms (27,000 pounds).
Why is wind turbine blade monitoring important to prevent blade failure?
Unfortunately, the size, height, and weight of wind turbine blades make repairs more difficult and costly. Sometimes, specialized equipment is needed, which adds to the cost. To promote energy production and safety, blades are inspected using a variety of methods or monitored remotely to identify issues. Common approaches include ultrasonic testing, visual testing, thermography, radiographic testing, and acoustic emission.
One reason why regular turbine blade monitoring is important is to identify issues. Ideally, if issues are detected, there may be lower-cost solutions that avoid replacing the entire turbine blade. Also, preventative maintenance can also help ensure the turbine is in good working order which can help avoid potential blade failure.
How does material selection impact wind turbine blades?
Material selection is critical for manufacturing durable, lightweight, and stiff wind turbine blades. Manufacturers produce blades from fiberglass and composite materials containing thermoset resin. Because wind turbine blades are also very large and weigh thousands of kilograms, they require a lot of materials to manufacture.
Ease of transportation is another important consideration because blades can’t be manufactured in several pieces and assembled on-site like a wind turbine tower. Because of the length and weight of turbine blades, they are difficult to maneuver on roadways during the construction and decommissioning phases of the project.
However, it is also a balancing act because the cost is critical for making renewable energy affordable. For wind energy to help rapidly phase out the use of fossil fuels, it needs to be an economically viable solution. Some materials for wind turbine blades are more durable, but can also make them more expensive.
In addition, sustainability is also a critical consideration, especially given the size of utility-scale wind turbine blades. Unfortunately, blades are currently not easy to recycle, which is creating waste management issues. Recent legislation in Europe bans turbine blades from landfills, but the United States lacks a national policy, and many end up in landfills.
Researchers at the National Renewable Energy Laboratory (NREL) are exploring the use of thermoplastic resins for wind turbine blades instead of thermoset resins. Although more research is needed, the initial results are promising for durability and recyclability.
This research is especially important because this wind turbine material is recyclable over and over as opposed to downccycling materials into low-quality goods. Also, thermoplastic resins need less energy to process the materials, which makes it easier to potentially manufacture the blade on-site, eliminating transportation issues. If feasible, this approach boosts the sustainability of wind turbine blades.
How can structural testing help advance wind energy technology?
Because the durability of wind turbine blades is so critical to asset performance, NREL tests wind turbine blades for structural validation with health and condition monitoring tests. For example, it completes fatigue testing on turbine blades which simulates lifetime load in the field in just several weeks.
Because fatigue from wind loading is the leading cause of wind turbine failure, understanding fatigue is critical. Testing can help increase the durability of wind turbine blades while increasing their reliability.
As the wind energy industry matures, researchers and wind turbine manufacturers are investigating ways to increase the lifespan of wind turbines, minimize downtime, and boost clean energy production. Examining potential maintenance issues related to wear and tear can be helpful in extending the life of wind turbine blades. Fatigue failure, lightning damage, icing, and blade erosion can all cause a wind turbine to wear out.
Wind energy professionals continue to look for ways to prevent such issues throught maintenance, monitoring, mitigation tactics, and proper wind turbine siting. These approaches can help extend the useful life of wind turbine blades, boosting reliable wind energy output.