Offshore wind farms are designed for a life expectancy of 20 years. The truth is that nobody really knows how long they can really last as there are no decommissioned offshore projects yet. Chances are that this 20 years is an over-conservative estimate and that the real economic life of at least the monopiles and tower could be much longer than designed for. If you realize that nacelle and blades constitute merely 15-20% of the total cost of a wind-turbine and monopile and tower the remaining 80-85%, it is easy to see that a dramatic lifespan increase of the latter beyond 20 years will equally dramatically reduce overall wind-turbine (and kWh) cost. Let’s assume that monopile and tower can exist for 60 years… that would mean that the cost of the turbine per year would decrease from 100 units in 20 years to (3 x 20 + 80) / 3 = 47 units, assuming tower + monopile cost of 80 of the total wind turbine price. That’s 47% of the per year cost.
[analysis.windenergyupdate.com] – Offshore wind farm lifetime extensions: why the ‘beyond 2020’ energy policy dialogue must start now
The agreed 20-year design lifetime means engineers can design to meet one consistent requirement, ensuring that new components can be guaranteed to work reliably and be insured for that period… For wind farms onshore, it may be cost-effective to simply replace nacelles and blades at the end of a 20-year design life, for about 15 to 20 percent of the cost of a new turbine. Because of space constraints and permitting expense, reusing the same wind farm area and layout makes sense, and turbine size cannot scale up much more for future land based turbines, for social reasons… Offshore wind is trickier, and complicating factors limit the potential for repowering.
Anecdotal “evidence” of wind energy longevity: the oldest windmill in the Netherlands, build long before America was ever heard off (1441 or older), still working fine (maintenance is everything). Open and working every Wednesday in Zeddam.
[source] Parisian icon Eiffel tower, a steel structure of meanwhile 128 years old. No reason to assume why it can’t last for another 2-3 centuries or more. The maritime environment is admittedly harsher than Paris, but still… 20 years?