Turbine surface innovators look to erase 2% output losses

New data has revealed the impact of leading-edge erosion on energy production and advanced protection packages now offer long term performance gains and optimized maintenance windows, industry experts said.

As the wind power industry matures, greater focus is being placed on Leading-Edge Erosion (LEE) as technology advancements and growing data on losses point to potential performance gains.

LEE occurs when dirt, moisture, salt or bugs create cracks or cavities on the first blade edge in contact with the air. Such defects compromise the aerodynamics of the whole blade.

Historically, many operators have not invested heavily in LEE after comparing the gains from leading edge maintenance against the associated availability losses.

Operators are now looking to maximize returns from higher-performance turbines in an increasingly competitive O&M market. In addition, fleet owners must mitigate losses associated with ageing turbines and respond to fresh environmental challenges in emerging markets.

The latest test results show LEE can have a startling impact on plant profitability.

“Our testing demonstrates that even minor LEE can cause Annual Energy Production (AEP) loss of almost 2% and a potential lifetime loss of up to 7%,” Dan Molyneux, Manager of Blade Services at Vestas, told Wind Energy Update.

Initial data from the UK's ORE Catapult Blade Leading Edge Erosion Program (BLEEP) has also indicated LEE repairs of moderate erosion can raise AEP by 1.5%-2%.

Studies by the U.S.' Sandia National Laboratories have shown onshore AEP can drop by as much as 5% in cases of light erosion and fall up to 25% due to heavy erosion.

             Estimated AEP loss due to Leading Edge Erosion (5 MW)

Source: Dr. D. Maniaci, 'Leading Edge Erosion Measurement and Modeling Campaigns', Sandia National Laboratories. (August 2016.)

Wind asset owners are starting to “better accept the industry research showing the AEP loss due to LEE and, consequently, are giving it more attention,” Molyneux said.

Growing challenge

Up until now, one of the biggest challenges for commissioning LEE work has been demonstrating the associated energy production loss, Molyneux noted.

Larger blades, faster tip speeds, and severe weather conditions magnify the impact of LEE and a growing bank of data is supporting action.

Higher performance blades have come at higher cost and this has increased the importance of LEE mitigation. In the onshore market, rotor diameters now surpass 100 meters with tip speeds over 200 mph.

                           Average capacity of installed turbines in Europe

Source: WIndEurope (2016)

New markets are presenting fresh environmental challenges and turbine ageing is also a key factor to consider, Francisco Garcia, O&M Manager at Enel Green Power, noted.

"We are building in new locations with aggressive conditions such as India and Brazil where we don’t have as much knowledge around soil impact upon blades,” he said.

Enel has a 6.8 GW global wind portfolio, including 2.4 GW in the U.S. Last month the company signed master supply agreements to build a further 3.5 GW of U.S. capacity.

For large fleet operators, performance degradation must be factored into investment decisions, Garcia said.

“[Around] 50% of our fleet is more than 10 years old, so we will experience ageing problems with erosion whilst rectifying the legacy of unmaintained blades,” he said.

Changes to localized weather patterns are also impacting performance, Claus Roedsgaard, Head of Blades at Siemens, said.

“The UK has experienced five years of extreme weather over the last decade, resulting in a 20% increase in rain, hail and snow. This does have an impact on the LE which will vary from site to site,” he said.

Protecting profits

Asset operators are now being offered a wider range of innovative solutions to mitigate LEE.

“Siemens as well as other companies in the wind industry are testing a lot of different systems and solutions,” Roedsgaard said.

Traditional prevent and repair materials have been putty, taping, gel and paint coatings.

Vestas uses flexible PUR paint, applied in a three-coat system upon manufacture, as part of its BlaseCare O&M package, Molyneux said.

This option "provides the best LE protection with minimal maintenance and easy repair whilst optimizing AEP, he said.

Coating solutions often require reapplication every few years, raising concerns over the availability impact and reliance on weather windows.

Vestas offers proactive maintenance of part of the O&M package and this can reduce downtime by "as much as 30%,” Molyneux said. Going forward, new coating solutions will last the full lifespan of the blade with minimal maintenance, he said.

Other solutions include partial LE covers and shields, including Siemens’ PowerEdge, IER Fujikura’s Blaid Protective Sheet and TRAC’s advantEDGE, which reduce the impact of weather conditions.

Siemens developed PowerEdge after company tests confirmed the flexible shell was a more efficient protection than a coating solution, Roedsgaard said.

PowerEdge is also designed to improve corrosion resistance and lift the asset power curve to achieve higher return on investment.

O&M service company GEV has also developed an innovative product to mitigate challenging weather and expand work windows.

GEV's Venture Habitat consists of a blade access platform and in house habitat structure which creates an artificial inflatable environment around the blade, Alastair Gadney, Managing Director of Specialist Divisions at GEV Group told Wind Energy Update.

"We use portable heaters or dehumidifiers to create the optimum conditions – it allows us to carry out repairs in otherwise prohibitive conditions," he said.

Wider deployment

Operators will continue to seek consolidated test data on the impact of LEE before these new solutions are adopted widely throughout the industry.

LEE investment strategies will depend on the operator’s O&M strategy and the exact age and location of the turbines.

Enel, for example, is currently prioritizing a wider baseline cost analysis of blade O&M activity across a 20-year lifespan, Garcia said.

Until more performance data can be provided on LEE, the sensible approach is for "low cost but frequent maintenance solutions,” he said.

Firms developing leading-edge products predict an upturn in activity in the coming years.

“LEE will continue to be a hot topic for the industry and is getting more attention from [Original equipment manufacturers] and owner/operators,” Molyneux said.

According to Gadney, the industry will soon be playing catch up.

"Repairing the legacy of LEE blade issues doesn’t happen overnight and the coming years are going to be very busy,” he said.

By Kerry Chamberlain