Why is the real world economic life of the wind farms roughly half the industry-claimed 25 years? See the 52-page Renewable Energy Foundation report “The Performance of Wind Farms in the United Kingdom and Denmark“. There’s a bit of math and statistics — the details are in the Appendix: Data and Methods.
There isn’t much data yet on offshore wind — but what data we do have should give pause to the government planners counting on enormous investments in new offshore wind farms.
For the United Kingdom the raw data were extracted from the Renewables and CHP Register database compiled by Ofgem. This government data is used in the administration of the market in Renewable Obligation Certificates (ROCs, otherwise known as transfers from taxpayers to wind operators).
The data for Danish wind farms used in this study comes from a database compiled by the Danish Energy Agency covering the characteristics and performance of all wind turbines from 2002 up to the end of August 2012.
The decline in operational performance is empirical fact. As I read the data the rate of degradation is not improving with newer generations. The technology is mature so I would expect initial performance to be worse as the best sites are populated first.
The causes of degradation from initial power-on are likely a combination of industrial aging (vibration which increases rate of bearing wear, etc), blade performance degradation due to chips, dings and accumulated coatings of bird and bat bits, and downtime. Usually aging equipment needs more servicing so you observe increasing outages of longer duration. Vestas and GE probably have good data on the performance degradation, but it isn’t obvious why they would be motivated to publicize what they know. They get paid at both ends, initial sale, replacement turbines and other parts.
I don’t know how much the operators care as the taxpayer subsidies are so high they make money no matter what. If the subsidies went away the whole “industry” would evaporate except special cases where the reliable grid is distant from demand while the supply of high quality wind is close to site of demand. And there is nearby hydropower which can be tapped for cheap backup storage.