Wind technology
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Understanding the scope of wind turbine blade damage is the first step to preventing it.

In order to get the maximum operational and financial benefit from larger turbines, and those in new markets, it is essential that turbine blades are serviced regularly and to a high standard.

This article first appeared in ESI-Africa Edition 1, 2019. You can read the magazine's articles here or subscribe here to receive a print copy.

Recent global growth of wind projects has increased the need for maintenance and repair work on turbine blades.1 As the market expands, so too does the demand for greater blade spans. Companies are heading this call by developing ever larger turbine technologies. The market must also keep watch over aging turbine blades, which need to be looked after to ensure they maintain performance and continue to provide the best return on investment. Equally, a well repaired turbine blade can be as good as a new one, if the repair remedies the damage and defects that have been hampering blade performance.

A variety of environmental effects such as extreme temperatures lead to the degradation of blades over their working lifetimes. This degradation caused by erosion on the leading edge affects the drag and the lift, and leads to reduction in aerodynamic efficiency and power production. Depending on the drag increase and lift decrease, the loss of the annual energy production of wind turbines can range from 2% to 25%.

Other issues that affect the functionality of the blades include tip damage and trailing edge cracks, which all naturally arise over the course of a turbine blade’s operational lifetime. As detrimental as these challenges may be to the operation of the wind farm, these problems are not insurmountable.

Repairs are performed to the internal structure of the blade, the external surfaces of the blade, and to attachments of the blade. This is all designed to make the blades more aerodynamic and increase annual energy production of wind turbines. It is also essential to be cognisant of the potential risks for the operations and maintenance (O&M) personnel to perform repairs and sustain the functionality of the blades.

Internal repairs

These repairs typically demand some of the most intensive work from technicians. Internal blade repairs include repairs to the bulkhead brackets and sealing, and repairs to the inner laminations; or removing foreign objects and retrofit solutions to optimise performance or minimise maintenance. Repairs to laminations can require extensive preparation of the blade, cleaning and ensuring a safe system for work within confined spaces, before the actual work of repairing the inner laminate damage can begin. Internal damages can be the result of sub-optimal manufacturing of, for instance, blade bulkheads.

Extensive damages such as lightning strikes can often mean the turbine blade has to be removed from the nacelle and dropped to the ground to be repaired, or replaced entirely. Internal repairs are often limited to newer turbine blades and required to remedy known deficiencies early on in a wind farm’s life.

External repairs

External repairs constitute the vast majority of repairs to turbine rotor blades themselves. External repairs typically involve patching and replacement of areas of the blade’s surface layers, which, as well as being exposed to the elements, need to withstand the mechanical stresses placed upon them as the blades flex and twist under loading. Rain erosion is recognised as one of the major causes of turbine rotor blade damage, and early identification and repair can prevent costlier repairs that could be required later on.2

Typical surface repairs can include simple scratches and scrapes of the top coat that may require light patching, or damage to the leading edge of the blade, or its protection, where it faces into the weather. The largest portion of external damages are to the gelcoat, which will require cleaning and sanding before the coat is applied, left to cure and then smoothed.

Repairs of aerodynamic add-ons

Blade attachments are designed to aid the aerodynamic properties of the blade and boost performance. Aerodynamic additions to blades are particularly important for ensuring that, as turbines age, owners continue to realise optimal performance from their assets.

The wind industry continues to grow at a rapid pace, with an additional 52GW of capacity installed in 2017, according to statistics published by the World Wind Energy Association.3 Understanding the scope of blade damage as it can occur on a wind farm is an important first step for O&M teams to ensuring turbines are online and working as efficiently as possible.

Global wind power capacity

The overall capacity of all wind turbines installed worldwide by the end of 2017 reached 539,291MW, according to preliminary statistics published in 2018 by the World Wind Energy Association (WWEA). In 2017, the industry added 52,552MW, slightly more than in 2016 when 51,402MW went online. This is the third largest number ever installed within one year, after the record years 2015 and 2014. However, the association expressed concern that the annual growth rate of only 10,8% is the lowest growth ever since the industrial deployment of wind turbines started at the end of the 20th century.

All wind turbines installed by the end of 2017 can cover more than 5% of the global electricity demand. For many countries, wind power has become a pillar in their strategies to phase out fossil and nuclear energy. In 2017, Denmark set a new world record with 43% of its power coming from wind. An increasing number of countries have reached a double-digit wind power share, including Germany, Ireland, Portugal, Spain, Sweden and Uruguay.

China is by far the largest wind power market, and it installed an additional capacity of 19GW in 2017, slightly less than in 2016, The country continues its undisputed position as the world’s wind power leader, with a cumulated wind capacity of 188GW in 2018. Together with an amazing deployment in solar power, the country is now well on its way to making renewable energy its main energy source. ESI

This article first appeared in ESI-Africa Edition 1, 2019.You can read the magazine's articles here or subscribe here to receive a print copy.

References

1. Altitec Blade Repair Atlas 2018

2. Bartolomé, Luis & Teuwen, Julie. (2018). Prospective challenges in the experimentation of the rain erosion on the leading edge of wind turbine blades. Wind Energy. 10.1002/we.2272.

3. World Wind Energy Association – Wind power capacity reaches 539GW, 52,6GW added in 2017.