Wind turbine coatings protect a valuable resource
In 2017, Britain broke installation records across Europe for new offshore wind power capacity, building 53% of the 3.15GW capacity installed. The UK is the windiest country in Europe, and a world leader in offshore wind. The world’s largest wind farm is the London Array, but that title will soon be overtaken by the Hornsea Project One offshore wind farm, under construction 75 miles off the Yorkshire coast. With 500-plus turbines currently connected to the grid and growth in wind power electricity generation and installation expected to continue it is of vital importance that such valuable assets are protected. Wind turbine coatings protect against the erosion and corrosion of the structure due to the harsh environmental conditions they face every day. They increase the wind turbine’s strength, lifespan, reliability, and durability.
In this article we look at the coating solutions for wind turbines both onshore and offshore, and the companies and their products on the UK market.
The challenges facing wind turbine coatings
Wind turbines harness the energy of the wind to create electricity. This means is they need to be built in places where wind is abundant, strong, and enduring. The windiest places on earth are also some of the most inhospitable and harshest environments. Wind turbine coatings need to work against the challenges wrought by the combination of environment and use. Some of the big challenges facing wind turbine coatings are:
- Corrosion – In the highly corrosive environments necessary for the most effective wind turbines, corrosion is a big problem. Sub-sea structures, splash zones, and the salt spray in the wind itself all present difficulties for the stability and strength of a wind turbine. Coatings need to provide the highest degree of corrosion protection.
- Leading edge erosion – The front edge of a wind turbine blade is subject to constant impact from airborne projectiles such as rain, ice, salt, or sand. The blade tip on a large turbine can reach speeds of 80m/s as it rotates, and pitting, delamination, and cosmetic failures form, compromising the blade’s integrity and developing into total blade failure. This ‘leading edge erosion’ is one of the biggest issues facing wind turbine coatings.
- High maintenance costs – Damage from rain and sand can reduce a turbine’s energy output by 20% a year. A turbine may be in continuous operation for 15 years and the coatings need to provide around the clock protection. The scale and location of these structures makes maintenance and accessibility a highly expensive task. The best coatings aim to be maintenance free for their lifetime.
The types and applications of wind turbine coatings
Both onshore and offshore wind turbines need coatings to ensure their optimum performance for their service life with the minimum of maintenance. Wind turbine coatings are applied to components including blades, towers, nacelles, foundations, and equipment. Like any coating the environmental conditions, service life, required durability, use, and substrate all need to be carefully chosen for to ensure the best outcome and performance. To that end, there are a variety of coating technologies available for the protection of wind turbines:
1. Polymer coatings – epoxy, polyurethane, acrylic, fluoropolymers
The Original Equipment Manufacturer (OEM) of wind turbines have a range of coating technologies and methods to choose from. Commonly used polymer coatings are epoxy, polyurethane, acrylic, and fluoropolymer. These coatings are applied either in a factory or in situ, depending on the relevant restrictions. Polymer coatings are chosen for their high performance properties: corrosion resistance, durability, chemical resistance, smooth finish, and toughness. Fluoropolymers have the added benefit of dirt resistance and to combat biofouling at the turbine base.
Polymer coatings are commonly applied as layered systems, rather than single coats. In this way the different properties of the coatings can protect other layers as well as the turbine, strengthening the protective system. Recent developments in the wind turbine coating industry include paint systems requiring fewer layers in order to reduce production time and cost. A common 3-coat system will use epoxy as the base coats and polyurethane as the top coat, using polyurethane’s UV resistance to protect the less-resistant epoxy.
A TYPICAL 3-COAT SYSTEM FOR WIND TURBINE TOWERS, FROM HEMPEL: Hempadur Avantguard (a two-component, zinc epoxy) as primer, Hempadur Mastic 4588W (a two-component, high build epoxy) as the intermediate coat, and Hempathane HS 55610 (a two-component polyurethane) as the top coat.
2. Metal coatings – zinc, aluminium
As well as zinc-rich epoxy coatings, wind turbines are often coated with metal coatings – non-ferrous metals such as zinc, aluminium, and its alloys. These metal coatings are applied through a variety of methods, including hot dip galvanising, electroplating, thermal spraying, and diffusion. Structural pieces undergo galvanising and spraying, where smaller pieces use electroplating, diffusion and galvanising.
In particularly corrosive environments (C5-M zones such as marine, coastal or high salinity areas), a duplex system is often used to protect turbines. A duplex system is the combination of a metal coating base layer and a polymer paint system, commonly used for offshore wind turbines. Even if the polymer coating fails or is damaged, the structure is still protected by the metal coating through both galvanic and barrier action. The duplex system is considered the toughest for offshore conditions.
AN EXAMPLE DUPLEX SYSTEM: The untreated steel is first coated with zinc through hot dip galvanising, then a two- or three-coat polymer coating system is applied on top. This may be two layers of epoxy formulations or a three layer system like the one outlined above.
3. Ceramic coatings – components and machinery
Protection of the structure of the wind turbine is vitally important, but the mechanisms also need protection from corrosion and from the wear of constant use. Rotating machinery such as bearings needs coating to increase their lifetime while decreasing maintenance costs. Ceramic coatings are inorganic coatings including aluminium oxide, aluminium titania, chromium oxide, and more. These coatings are hard, low friction, abrasion and wear resistant, anti-galling, corrosion resistant, heat resistant, and durable.
Ceramic coatings are also finding applications with the blades of wind turbines. This is in part because ceramic coatings have a greater abrasion resistance than polymer coatings, an important factor in combating leading edge erosion and preventing the constant impact of projectiles from damaging the blade.
The wind turbine rotor blade coating process
Wind turbine blades are made from aluminium, wood, or a fibreglass-resin composite (for those blades too large for wood or aluminium). Coatings can be applied with spray, roll or brush applied to rotor blades made from aluminium wood, but there are two different methods for coating a fibreglass-resin composite blade: in-mould and post-mould application.
A moulded rotor blade is formed as two separately moulded halves, which are then joined. An in-mould coating application means the mould is produced with a gelcoat, the benefit of this being that a polyurethane gelcoat is easier to work with in the final surface preparation than a fibreglass substrate. Post-mould application is the application of coatings after the blade has been formed. Where in-mould coating is important for the performance of the entire blade, post-mould coating is focused on protecting the leading edge.
In-mould coatings use a similar resin to that used for the mould – epoxy or polyurethane, for example – and by incorporating part of the coating process in the blade formation it cuts down on the time and cost of coating. Post-mould coatings are also often epoxy or polyurethane based, with polyurethane as the final protective topcoat in a multi-layer system.
Wind turbine coatings products and manufacturers in the UK
The growth of the wind energy sector has seen a corresponding rise in the number of coating companies catering to wind turbine coatings. The industry is currently dominated by a few big companies, with many smaller companies jockeying for position. The top players are AkzoNobel, Hempel, PPG, Jotun, Aeolus, Teknos, and Sherwin-Williams. AkzoNobel’s coatings are used to protect the London Array windfarm, and Hempel coatings protect some 50% of the onshore and offshore towers around the globe.
There are a vast range of wind turbine coatings available in the UK. It is important to consult with coatings experts when choosing any protective coating or coating system in order to ensure the best performance of both the coating and your asset. The cost of coating onshore structures ranges from £15-20 per m2 (depending on coating, method and other variables), but repair work costs more. For offshore structures, on-site repair work can cost up to 50 times more than the initial application cost. Below is a table outlining a few of the wind turbine coating products available.
If you would like advice about wind turbine coatings, or are looking for a coating for your project, get in touch! Our experts are here to help. In cooperation with our coating partners, we will connect you with the coating solution for your needs.
|Coating Company/Brand||Wind Turbine Coating Product||Description|
|AkzoNobel||Intershield 300||A two component, abrasion resistant aluminium-pigmented pure epoxy coating providing excellent long term anticorrosive protection for offshore structures.|
|Hempel||Hempadur Avantguard 750||A two-component, activated zinc epoxy primer for long-term protection of steel in severely corrosive environments.|
|Jotun||Jotamastic 87||A two component epoxy-mastic for repair and maintenance. Anticorrosive coating for a range of substrates.|
|PPG Industries||Selemix||A polyurethane topcoat for turbine blades to protect from erosion.|