Extending the lifetime of offshore wind turbines

Wind turbines on land and offshore in a storm

Wind farm with rows of wind turbines both on land and offshore during a winter storm at the shore of the IJsselmeer in the Noordoostpolder, Flevoland, The Netherlands.

By Fawzi Abou-Chahine, National Physical Laboratory (NPL).

Close to 90% of global offshore wind energy is generated by Europe, with the UK and Germany leading the market, while China and Denmark are close behind.

Between September and October 2017, nearly 10% of the UK’s energy was produced from offshore wind alone. This shows the UK is well on its way to meeting its target to generate 15% of its energy from renewable sources by 2020.

One key reason for the success of offshore wind energy is that much of the technical knowledge is comparable to the more mature onshore wind market. Offshore wind energy is more stable at sea than it is on land and there is less opposition from the public, which means bigger and more efficient turbines can be used. This results in a decrease in the overall cost that further drives investment.

Wind turbines are expected to operate for over 100,000 hours and last 20 years, but during that lifetime their energy efficiency will decrease. Although newer and larger turbines with longer predicted lifetimes can be built in their place, investors are keen to preserve and extend the lifetime of their current assets. To support this, we are working alongside energy suppliers to tackle the challenges the industry faces, such as corrosion and component testing.

Overcoming the challenges to extend turbine lifetime

One of the most susceptible parts of the wind turbine are the blades, which have to balance strength, stiffness, and longevity with cost-effectiveness, weight and fatigue resistance. The leading edge of a blade is slowly eroded by the environment over time, especially in offshore settings. At high rotation speeds, rain droplets augment erosion, while any moisture that condenses on the blade can freeze, damaging the surface and minimising efficiency by reducing aerodynamicity.

In Europe, the annual costs associated with leading-edge erosion, such as operational downtime and maintenance, are likely to exceed millions of euros. We are developing innovative and cost-effective solutions to limit the erosion and extend turbine lifetime by designing super-hydrophobic films that cause water droplets to roll off the surface.

In the future, blade lengths are likely to exceed 90 m, but single components of such length are impractical and expensive to transport. Modular designs are being considered and we have been testing how different joint designs between modules can withstand both low and high loads under regular and low-frequency cycles. Currently, manual inspections of assets require them to be shut down and to have a trained investigator on site, in a so-called ‘man-on-rope’. This can cause lengthy delays and high costs for the operator.

Piloted drones offer the potential to reduce operational downtime by quickly accessing multiple turbines to provide a visual check of the status of specific blades. This initial inspection allows more targeted use of manual inspections, thereby reducing the occupational risks associated with manual turbine maintenance. We collaborate with service providers to create innovative solutions like this that address common industry challenges.

Going forward, there are many more financial, environmental and practical challenges that need to be overcome to extend the lifetime of offshore wind turbines. We are working with companies across the energy sector to support numerous activities that enhance asset integrity and life-extension through operation and maintenance monitoring, environmental measurements and new development design. This supports the offshore renewable sector to improve the design, installation, commissioning and operation of offshore wind assets, which will, in turn, drive down operational costs and help to continue in making offshore renewable energy cost-competitive compared to conventional fossil-fuel alternatives.

Fawzi Abou-Chahine, Business Development Specialist for Energy and Environment at the National Physical Laboratory (NPL).

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