Beautifying your Blades: How to make them run better and longer
Blades account for 20% of a turbine’s value. Concerns are increasing now that more turbines are nearing a decade of service. We look at options, materials and devices that are emerging that could transform maintenance.
By Elisabeth Jeffries
“The driver for turbine management should be looked at in terms of lifetime costs. Companies are still not thinking of that enough to keep costs down. The focus is still driven by capital equipment expenditure,” remarks Benn Faulkner, director of Renewable Advice, a UK company providing technical and practical support for all aspects of wind turbine blades.
However, Faulkner also contends the blade is a previously overlooked feature of wind turbine maintenance and monitoring, but may finally start to get the attention it requires. Marcel Bruins, international project manager and blade expert at independent wind farm service provider Availon, takes a similar view. “Blades are 20% of the value of the turbine but have often been neglected. It’s still a problem today. But awareness of blades is improving,” he says.
Management of onshore wind parks tends to focus on the gearbox, castings and other parts of the tower. Yet each part of the turbine, which usually has to run for 20 years, has to weather the full force of the elements. Cable faults and infrastructure delays are among the most common problems arising from bad weather. Occasionally, a blade may break following a lightning strike. But for the most part, operations and maintenance of the blade is focused on general wear- and-tear caused as the blade’s leading edge is eroded by wind, dust, sand and other particles. Over time, the aerodynamics of the blade are disturbed, so maintenance work focuses on minor but regular repairs. Site examination typically takes place on a biennial basis.
Technical solutions are available. Two devices could plug a major gap in wind turbine monitoring, such as lightning strike registration systems, which could now be fitted to turbines. “Lightning strikes are a main reason for blade damage,” says Bruins, “however, present computing does not monitor blades. The system would warn of a strike within a few seconds.” Up to now, strike effects have only been observed as burn marks perhaps months later during a regular inspection.
Blade damage may also be affecting turbine performance without management even knowing. Bruins also suggests more sensors could be attached to blades as part of the general remote computerised condition monitoring systems already in constant use for the rest of the turbine. “You could equip blades with vibration sensors, which could detect defects in an early stage. But mostly the investment is higher than the financial advantages, such sensors would generate. It’s because damage to blades is not directly visual that more time is invested in other parts,”says Bruins.
The use of winglets is another more recent innovation in blade design. “Winglets were introduced into the market a year or so ago. They are placed on the tip of the blade and enlarge its surface without extending the length, thereby catching more wind. It makes a significant improvement to the performance of the turbine,” explains Bruins.
However, for the most part cost has deterred project managers from introducing these innovations. This includes the use of particular materials, which have a major effect on longevity and performance of the blade. “Carbon fibre makes the blade more severely weather-resistant than glass fibre. It’s a matter of: would you be prepared to pay extra money for the small advantage you have from carbon fibre? Cost is a large issue,” points out Bruins.
Similarly, managers need to weigh up the pros and cons of using condition monitoring systems on blades: “If you look at the cost of turbines, it’s not really expensive in proportion to that. On the other hand, if you do not detect damage, which could lead to blade loss, the cost could be 10-20 times higher,” states Bruins. Yet although wear-and-tear is worsening over time, Faulkner maintains managers still keep to low-tech and therefore relatively cheap solutions.
“There is a gradual shift from a small group of people taking blade issues seriously to utilities becoming aware they may not last 20 years. There are not enough installations of smart monitoring systems due to economical viability. For leading edge wear-and-tear, one of the best solutions for the UK is still 3M tape, which has been around for 30 years,” argues Faulkner. The impact of employing longer blades (rising from 5 to 80 metres in 30 years) is as yet unknown.
He indicates innovative production materials and techniques may be necessary given the extra time required to make longer blades; using existing coatings and adhesives may affect long-term blade performance. “For super-long blades over 80m, blade manufacturing and repair becomes a bigger problem. A greater volume of material means it is more challenging to manage,” he says.
Any form of proactive measure could have an initial outlay when it comes to prolonging blade operations, but as lessons are learned and retold throughout the O&M part of the wind turbine sector, materials, sensors and maintenance checks will evolve so that blades are more cost effective and for longer-of that there is no question. But which party will be more proactive—the manufacturer or the end blade user-to demand such elements are pre-built into the blade designs and operations is still a work in progress.