The wind generators are mere machines with rotating components such as shafts, gears, bearings and seals, all with a finite life expectancy. One of the advantages of modern engineering is that such components are produced to fine tolerances and a consistent quality. Whilst this may mean a long life expectancy, it also means when the components begin to reach the point of running hours where wear and fatigue signal impending replacement or failure in one machine, the same will be occurring in all machines with similar running time.
All windfarms having had all the windmills commissioned at the same time will likely need all units being shutdown for major overhaul at about the same time, and with all windfarms built so far across Australia within a fairly short period of time, whilst it may be some years away, there will come a time when all those currently in operation will see reduced availability affecting output over an extended period of time.
That is assuming there are no unexpected failures, in which case, just as happens if an aeroplane experiences a serious failure results in all similar planes being immediately grounded, if for instance a windmill loses a blade, all windmills with similar blades will probably be immediately taken out of service until the problem has been diagnosed and safety checks undertaken. If the problem happens to be diagnosed as a design fault, that could pose a serious shortage of electricity over an extended period of time given how little reliable backup is being built into grid.
