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RENEWABLE ENERGY


COMPETITIVE EDGE


Why it pays to think “cutting edge” for leading edge protection


T


he growth of wind energy is exceptional – both in terms of installations and physical size. In Europe alone, it’s predicted to


overtake gas installations and become the largest form of power generation by 2020, supported fi rmly by a mammoth addition of 4.9GW in capacity during just the fi rst half of 2019. Meanwhile, the size of wind turbines has reached incredible heights, with LM Wind Power unveiling the world’s longest blade at a staggering 107m in length. T e importance of a high-quality and easy-to-apply leading edge protection (LEP) coating has never been more important to keep up with the demand from this blossoming industry.


PRECIPITATION AND POWER GENERATION


Although it may seem innocuous, the impact of debris and weather (particularly rain) on a blade can cause considerable damage. Using some rudimentary mathematics, the impact pressure of rain droplets can be estimated using modifi ed water hammer equations. Based on a 2mm


26 www.engineerlive.com


diameter droplet and an 80m/s tip speed, the pressure imparted by the raindrop is estimated at 120MPa. T is value is already higher than the yield stress quoted for some blade materials. T is type of damage manifests itself as pitting on the blade’s surface, especially on the leading edge, where the most impact will occur. T is deterioration causes a reduction in aerodynamic effi ciency and subsequently a loss in operating effi ciency. Some studies show that leading edge erosion can result in a drag increase of up to 500%, culminating in a decrease in annual energy output of up to 20%. T e eff ects of this damage can be apparent in as little as two years. As wind turbines can reasonably be expected to perform continuously for 15+ years, this is a signifi cant problem for turbine operators. A variety of studies have investigated the costs and strategies of operations and maintenance (O&M) for wind power. Some have found that these O&M ventures can account for as much as 30% of the overall per-MWh-cost for wind turbines. Other studies have looked at


failures on a component-by-component basis. Depending on the type of turbine, the blades can account for up to 22% of failures. T e resulting high costs means many companies are moving towards a preventative and predictive approach, especially in off shore markets. As well as being more costly to maintain,


off shore wind turbines are also more susceptible to damage. As off shore wind is not limited by acoustic emission, the tip speeds and blade lengths tend to be much larger, thereby increasing the impact velocity of the rain droplets.


THE CHALLENGE T e diffi culty with blade maintenance is not only fi nding suitable materials and methods for protecting new blades but, more commonly, repairing damage to those already in the fi eld. T e associated challenges can be twofold. Firstly, materials science – developing materials and techniques that will protect blades throughout their useful lifetime. Secondly, application – applying the protective measures in the fi eld, often in


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