Here are the average capacity factors for offshore wind farms in UK waters, newly updated to include data to the end of 2019 (though there are still some figures to come through for the last couple of months of last year, for the smaller windfarms). There are 37 operational windfarms presented here, and two closed demonstration sites.
2019 set a new record for the highest annual average capacity factor for a UK offshore windfarm: Hywind Scotland achieved 55.3% in the calendar year 2019.
Hywind Scotland has a median output of 59.1%. The next-closest to this was Walney phases 3&4, which has a median output of 48.4%. The lowest is Rampion: median 19.3%. Median aggregate output for the fleet of 25 windfarms that have detailed data is 36.3%. Hywind, the floating windfarm, has behaved differently to any windfarm we’ve seen before.
At the other extreme, Rampion has had several prolonged faults, harming output. The load-duration curves at the bottom of this page show the differences in distribution of outputs: click on the individual farm names in the legend, to toggle the display of individual curves.
You might be interested in comparing these with the capacity factors and load-duration curves for Belgium, Denmark and Germany.