Wind turbines, including the costs associated with blades, towers, transportation and installation, constitute the largest cost component of a wind farm, typically accounting for around 75% of the capital cost.
Wind turbines tend to be type-certified for clearly defined external conditions. This certification is requested by investors and insurance companies, and states that wind turbines will be secure and fit for their purpose for their intended lifetime of around 20 years for onshore projects and 25 years for offshore.
The above figure illustrates the main sub-components that make up a wind turbine, and their share of total wind turbine cost. Note that the figure refers to a large turbine in the commercial market (5 MW as opposed to the 2 to 3 MW machines that are commonly being installed). The relative weight of the sub-components varies depending on the model.
Wind turbines are priced in proportion to their swept rotor surface area and generally speaking in proportion to roughly the square root of their hub height. The size of the generator of a wind turbine plays a fairly minor role in the pricing of a wind turbine, even though the rated power of the generator tends to be fairly proportional to the swept rotor area.
The reason for this is that for a given rotor geometry and a given tip speed ratio, the annual energy yield from a wind turbine in a given wind climate is largely proportional to the rotor area. In relation to tower heights, the production increases with the hub height roughly in proportion to the square root of the hub height (depending on the roughness of the surrounding terrain).
It should be noted that the generator size of a wind turbine is not as important for annual production as the swept rotor area of the turbine. This is because on an optimized wind turbine, the generator will only temporarily be running at rated (peak) power. It is therefore not appropriate to compare wind turbines with other power generation sources purely on the basis
of the installed MW of rated generator power.(10) One has to keep in mind that the energy of a wind turbine comes from the swept rotor area of the wind turbine. The swept rotor area is thus in some sense the field from which the energy of the wind is harvested.
Wind turbines built for rougher climates, cold temperatures, in deserts or for offshore conditions are generally more expensive than turbines built for more clement climates. In addition, stricter technical requirements from transmission operators in recent years have added to the technology cost.
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