Capturing renewable energy involves exposure to the elements, some of which can wreak havoc on machinery, particularly wind turbines. Polymeric materials have been able to solve these maintenance problems from the base of the turbine to the tip of the blades, writes Thomas Belli

The renewable energy market continues to go from strength to strength, with 2016 marking a series of impressive milestones versus conventional, fossil-fuelled energy.

Certainly, one of the most remarkable was global investment in new renewable energy infrastructure surpassing that spent on new fossil infrastructure. This statistic reinforces how climate change policies and low-carbon initiatives have improved the cost-competitiveness of renewable technologies, making them a much more affordable and accessible form of energy.

Significantly, as funding and support for renewable projects begins to outweigh that favouring traditional energy sources, it is necessary to ensure a continued return on this investment.

Blade tip damage is the largest problem for
Blade tip damage is the largest problem for the wind industry

This can be achieved successfully through effective maintenance of renewable assets and management of the issues affecting them. Whether through immersion in corrosive sea water, contact with high geothermal temperatures or aggressive abrasion imposed by gale force winds, the methods of harnessing greener energy are not without complications.

By its very nature, capturing renewable energy involves exposure to the elements, some of which can wreak havoc on the machinery, equipment and structures used throughout the industry. This is true for geothermal, solar, tidal and wind power, all of which suffer from a variety of different damage mechanisms.

The expansion of the renewable energy sector is certainly positive for the planet. However, maintaining the existing green assets across the globe is a problem that confronts many energy companies.

Like the maintenance of any other industrial asset, owners and operators require cost-effective solutions that can be carried out quickly and easily, yet ensure long-term results.

One such innovation is the use of polymeric solutions for a variety of maintenance issues in most power generation markets. This has been particularly successful for the repair and protection of renewable equipment and facilities. The biggest progress has been achieved in the wind power industry, where polymeric materials have been able to solve maintenance problems present from the base of the turbine to the very tip of the blades.

From the vast investment in new renewable infrastructure, perhaps the biggest beneficiaries were offshore wind farms, which have boomed in the past 12 months. In total, capital spending commitments for this form of green energy reached a record $30 billion in 2016 according to Bloomberg New Energy Finance.

Further to these pledges, there are offshore wind farm projects under construction in European waters that equate to 27 GW in capacity. This adds significantly to the global wind power capacity of 433 GW logged in 2015.

Despite being one of the leading forms of renewable energy, the design of wind turbines – and the environments within which they operate – pose a variety of different problems from a maintenance perspective.

Corrosion of components and foundation damage are among some of these maintenance issues. However, it is recognized that the single largest problem for the wind power industry is leading edge damage.

Blade tips can revolve at up to 300 kmph in widely-fluctuating temperatures, humidity levels and rates of UV exposure. Coupled with the damage from a variety of impact and abrasion factors including rain, dust, ice, insects, birds and lightning, this can cause substantial erosion of the substrate.

Evidence suggests that damage to the leading edge can lower annual energy production (AEP) of a wind turbine, with energy losses estimated at between 4 and 20 per cent if the erosion damage is severe.

This generates a reduction in aerodynamic efficiency, affecting the energy output as well as exacerbating the damage to other turbine components. Imbalance between the blades can cause wear and damage in the shaft and gearbox, in addition to putting further stresses on the tower and base. Overall, this reduces the tower’s operational life expectancy.

Polymeric solutions can be applied at the OEM stage
Polymeric solutions can be applied at the OEM stage

Alternative solutions for this problem include fillers, binders and tapes, yet none of these will provide extensive, long-term repair and protection. In these scenarios, repairing the damaged substrate can be easily achieved with reconstructive composites and protective coatings.

Following sanding of the damaged area and adequate surface preparation, an epoxy-based repair composite can rebuild the eroded blade to original specifications, adhering extremely well to FRP substrates.

As a protective layer, the moulded surface can be overcoated with one of a range of erosion- and corrosion-resistant epoxy systems. Brush- and spray-applied, they offer a high level of durability and flexibility versus the threats of abrasion and impact.

Rather than simply a reactive option, these solutions can be applied proactively at the OEM stage, protecting the most threatened areas before they enter service.

This approach was taken by an industry-leading Japanese engineering company, which specified Belzona 1341 (Supermetalglide) as a protective coating for the leading edges of turbine blades during manufacture. Over an estimated ten years since their original installation across sites throughout the US, these blades have withstood the effects of erosion beyond their anticipated life expectancy.

It is not just leading edge damage which can be rectified to improve the output and operation of wind turbines. Some of the other major issues that befall these structures involve the components in the nacelle.

Protecting brake drums, sealing cables, as well as the repair of worn and damaged shafts can be easily achieved using polymeric solutions. Meanwhile, the integrity of the nacelle, tower and platform can all be upheld by using seamless, weatherproof and waterproof protective coatings, maintaining wind turbines despite the often-adverse weather conditions found in their operational environments.

In addition, ensuring the stable foundations of these structures is essential. Trends show that blades are getting bigger and bigger, as rotor diameters have steadily increased over the last 20 years in line with higher output capacities. Offshore blades in particular are estimated to reach a staggering 190 metres in diameter by 2030, nearly double the size of blades today, making firm foundations integral to keeping turbines upright.

Therefore, the repair and rebuild of concrete around the base can be achieved with concrete repair systems and the surface protected with coatings.

 
Protecting components can be easily achieved

Geothermal and tidal

Although there is an array of maintenance solutions in place for wind turbines, this does not mean that other renewable energies are neglected in terms of their repair and protection. There are equal stresses placed upon the likes of tidal, wave and geothermal energy. Therefore, the solutions adept at resisting corrosion, erosion and chemical attack will translate well into these new application scenarios.

For example, the characteristics of geothermal fluid can vary significantly, including temperature, chemistry and non-condensable gas content (NCG), all of which can have an extremely corrosive effect on power plant components.

The negative impact on the efficiency and function of the geothermal power plant can manifest in pipes, turbine casings, heat exchangers and tanks. According to reported statistics on the state of geothermal technology, the use of corrosion-resistant materials, such as protective coatings, can reduce costs by an estimated $0.25/kWh.

When extrapolated to the global electricity generation of geothermal resources in 2015 (71 TWh), savings through corrosion mitigation can exceed well over $100 million, while also helping to improve the efficiency of deteriorated equipment.

Moreover, the repair and protection of turbine blades is not isolated to wind power, as this type of application has a similar role to play in the tidal power industry. At sea level, water is 784 times denser than air, so tidal turbine rotors can be much smaller but still generate equivalent amounts of electricity.

Cavitation, a problem that manifests itself because of a pressure difference in a fluid, is prominent in this situation and can threaten the integrity of the blades, much like erosion on wind turbines.

By employing a cavitation- and erosion-resistant solution, the in-service life of tidal turbines can be extended, protecting them against deterioration emanating from turbulent flow.

Green intentions

With the rapidly growing presence of renewable energies in more and more countries, it is clear that the world’s emerging economies are showing similar interest in the low-carbon transformation of global energy sourcing.

In fact, they are matching many of their better-equipped counterparts. This highlights that the wave of support for green energy is truly growing and capturing the world’s attention.

As this sector expands, there will continue to be investments of increasing magnitude; however, it is essential that these assets are maintained and remain operational, providing an effective return on investment. Polymeric repair and protective solutions have already had proven success in the power industry and have made notable impressions in the renewable energy market to date.

Extensive testing and long-term involvement with industry-leading companies certainly demonstrates that these systems can effectively manage the frequent issues associated with erosion, corrosion and abrasion.

Thomas Belli is Marketing Assistant with Belzona, a leading company in the design and manufacture of polymer repair composites and industrial protective coatings for the repair, protection and improvement of machinery, equipment, buildings and structures. www.belzona.com