Wind Power

Nickel makes a hard case for wind power

Wind power is a fast-growing energy sector, with almost 600 gigawatts in operation at the end of 2018, providing about 5% of global electricity demand. Wind power, along with solar, biomass and hydro power, is one of the renewable energy sources replacing dependence on fossil fuels.
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Article by Geir Moe, P.Eng, Nickel Institute

Utility-scale wind turbines are now exceeding outputs of five megawatts (MW). Measured in tonnes of material per MW, wind power is the most iron and steel-intensive of all power generation methods. Existing designs use about 300 tonnes of iron and steel per installed MW. Table 1 lists some major components in a wind power system, the typical materials of construction and their purpose. Nickelcontaining materials can be present in various components as shown.

Table 1. Major components in a wind power system
Component  Function/Remarks  Materials 
Gearbox Gears increase the rotational speed of the rotor shaft to the high speed needed to drive the generator  Heat-treatable carburising steel 18CrNiMo7-6; Austempered ductile iron (ADI)
Generator  Convers mechanical energy into electrical energy Heat-treatable CrNiMo steels
Main frame Supports the entire turbine drive train High-strength low alloy plate; Spheroidal cast iron or ADI
Main shaft Transfers the rotational force of the rotor to the gearbox Heat-treatable CrMo steels; Shperoidal cast iron or ADI
Rotor hub  Holds the blades in position as they turn Spheroidal cast iron or ADI
Screws, studs Holds the components in place; designed for extreme Heat-treatable CrMo and CrNiMo steels

Toughness and higher strength

High strength Austempered Ductile Iron (ADI) is a cast iron material in which carbon is present as graphite nodules in a matrix of ausferrite, a mixture of ferrite and austenite that provides the high strength and ductility of ADI. The addition of nickel, molybdenum and copper as shown in Table 2, delays pearlite formation to enable ausferrite formation and promotes hardenability. ADI possesses twice the tensile and yield strength of standard ductile irons, and 50% higher fatigue strength. Thus, ADI offers considerable weight savings compared with standard ductile cast irons for the fabrication of the larger castings such as hub, hollow shaft and gearbox housing.

Table 2. Nickel-containing materials used in wind turbine fabrication and installations
     Alloy content (wt%, min./max.) Minimum yield strength MPa <2'' thickness
Steel grade  Material number C Si Cr Mo Ni CU
18CrNiMo7-6 1.6587 0.15/0.21  ≤0.40 1.50/1.80 0.25/0.35 1.40/1.70 -
ADI   3.5/3.7 1.9/2.3   0.15/0.30 0.6/2.5 0.6/1.0  
S690QL 1.8928 0.02 max 0.80 max 1.50 max 0.70 max 2.0 max 0.50 max 690
S890QL 1.8983 890
S960QL 1.8983 960

High-performance gear steels

Wind turbine gear applications require long fatigue life and high toughness.

A hard case and a tough core produce a wear-resistant gear, capable of handling high impact loads. High-performance NiCrMo carburising steels as shown in Table 2 provide deep hardening ability and strong resistance to fatigue. Currently, the grade 18CrNiMo7-6 is the standard gear steel for windmill gearboxes.

The wind energy business has also a large impact on other equipment, such as large mobile cranes, which are required to erect the turbines. Because of the hoisting heights and weights involved, crane booms made from ultra high-strength steel are required. Applicable steel grades are in the range of S690 to S960, (Table2).

Crane booms are usually made from quench and tempered steel plate and may possess up to 2% nickel additions.

Stronger and more consistent winds are present further from shore. Typically, these sites are in water more than 60m (200 ft) deep, which makes fixed-based turbines impractical. The wind power industry is testing floating wind turbines, such as the Hywind Scotland farm comprised of five floating turbines with a total capacity of 30MW. The wind power industry is even considering larger turbines exceeding 10MW output.

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