but I spend a certain amount of time looking for trends in data.

So I had a quick look at the raw data (the source Danish spreadsheet with numbers for individual turbines) and yeah, if you graph turbines over 15 years, you can see a clear decline trend.

Depending on the data you choose to look at, you can get something approaching the 20% (i.e. decline from 22% to 18% load factor) cited by ref.org.

Then I thought about the turbines which have 15-year time series. Sure enough, all of them are 600kw or less. The smaller (i.e. older) ones have higher decline rates, probably over 20% over 15 years. The larger machines have smaller decline rates.

Then of course, if you look at the classes of machines which don't yet have 15 years of service, the picture changes...

No surprises here. "Lying with data 101" covers it.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}