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.