Wind turbine coatings increase durability & decrease maintenance costs
Canada belongs to the group of countries that make the most use of wind power; it is currently listed the 9th on a global scale having a total installed capacity of 12, 239 MW. The Canadian history of wind power has its roots in Ontario, Quebec and Alberta where the energy generation started in the early 90’s. Now some 3 million households get their energy from wind power resulting in 6% of the country’s total energy needs. In 2017 $800 million were invested in new wind farms. Canada’s largest wind farm is Riviere-du-moulin in Quebec having 175 wind turbines with capacity of 350 MW. The plan is to increase the capacity to 55 GW fulfilling 20% of the total energy needs by 2025. Given the growth in wind power electricity generation and installation, it is of vital importance that such valuable assets are protected appropriately. 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 as well as reducing the need for costly maintenance.
In this article we take a look at the coatings for wind turbines both onshore and offshore, and the companies and their products on the Canadian market.
How wind turbine coatings protect the resource
Wind turbines harness the energy of the wind to create electricity. This means that 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. The right wind turbine coating provides protection from the three most threatening hazards faced by the windmills being:
- Severe 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. The wind turbine coatings need to provide the highest degree of corrosion protection.
- 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 wind power coatings aim to be maintenance free for their lifetime.
- 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 80 m/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 challenging wind turbine coatings.
Wind turbine coating types and application for complete protection
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 for wind turbines
Epoxy, acrylic, polyurethane and fluoropolymer high performance coatings
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 3 layer system by 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 for structural pieces
Zinc rich epoxy coating, zinc and aluminium through thermal spraying, galvanising, electroplating and diffusion
Metal coatings are a crucial part of coating wind turbines; it can be applied on any metal surface from large structural pieces to the tiniest components.
In particularly corrosive environments (C5-M zones), 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.
A 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 for components, machinery and rotor blades
Inorganic coatings such as aluminium oxide, aluminium titania, chromium oxide, and more
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. 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 ways of coating wind turbine rotor blades
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 to rotor blades made from aluminium and 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. In this process the wind turbine coatings can be applied in two phases:
- In mould coatings – when the mould is produced with a polyurethane gelcoat.
This type of coating contributes to the overall quality of the blade and makes the unfinished blades easier to handle than a fibreglass surface. The in-mould coatings are usually epoxy or polyurethane based and the application is time and cost efficient.
- Post-mould coatings – applying the coating after the blade has been formed.
These coatings focus on protecting the lead edge from erosion and they are often epoxy or polyurethane based and follow the order of a regular 3 coat system (polyurethane is the top coat).
Wind turbine coatings in Canada – Products from top manufacturers
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. Hempel coatings protect some 50% of the onshore and offshore towers around the globe, and are one of the most used brands in Canada, too.
There are a vast range of wind turbine coatings available in Canada. 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 CA$ 25-35 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||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.|