Wind machines are not turbines because they use no turbo-compressor to work. Instead a gearbox converts the rotation of the blades into an axial drive to turn the generator.
The rotor subjects the bearings on which the main shaft rests to stress and strain, especially during high winds, which means, according to wind power engineers, that the gearbox life expectancy is around ten years.
According to American experts, replacing a gearbox can take up to a week, because of its cost, transport to site costs, crane hire and on-site labour, resulting in a bill of up to $500,000 per machine, plus downtime.
Furthermore insurance companies are reluctant to extend warranties as machines age.
I haven’t seen estimates of the cost over time of gearbox replacement from the wind power industry in Scotland.