Like any other modern gear-driven electrical machinery, wind turbines require regular maintenance and have a limited lifetime.
... and of course a significant factor is that work must be done hundreds of feet in the air
Complex controls, gearboxes, inverters, cooling and electrical systems do not last forever and become more expensive to maintain as the years go on. I would assume a common lifetime for a machine like this would be 15 to 20 years.
Turbine vendors come out with improved designs. Science and industry marches on..... Bankers and developers sharpen their spreadsheets and the new Biden Government will come up with a new type of wind turbine financial incentive.
All of these factors affect what will be the useful and economically attractive lifetime.
I am aware of at least two huge windfarms where older turbines, only a few years old, were replaced by newer, higher capacity units just a couple of MWe larger. There was massive foundation rework and strengthening.... Why ? ...... Not because the units were at the end of their useful life, but because the spreadsheets and the bankers said that it was an attractive thing to do...
Jut my two cents ....
MJCronin
Sr. Process Engineer