[japanuspus]

Wind turbines have a design lifetime of 20 years, but most will last much longer (source: I work at a large offshore wind company).

There are two reasons why everything is still built for 20 years: Firstly, there is not pressure on the projects to increase lifetime, because the deprecated value today of further production in year 21 is basically zero. Secondly, the turbines we installed 20 years ago were so small that there is really no reason to keep them going.