In the UK, curtailment seems needed due to power transfer capacity issues.
In Sweden it is purely due to grid stability reasons. As wind does not work as a baseload power source this becomes problematic as too much wind power generation can then negatively affect profitability for nuclear and hydro which are baseload power sources.
I would be interested to see how stable wind power production is across all hours and throughout the year in the UK. I imagine it's better than here, but is it good enough to support an industrial nation?
It's been very windy recently so we are hitting around 40-60% wind power at the moment but there were moments last year where we were only getting 3% from wind power if it isn't very windy and unfortunately that means using more gas turbines for power which is an expensive source of energy at the moment.
But then wind power can only be part of a mix of energy sources, with a strong supply of baseload power backing it.