This is of course expected, and not a knock on the achievement at all. Wind is in its early days, and growing quickly. There's only so much installed capacity, so it's going to reach it's peak percentage of the energy mix when the demand is lowest. And it will only do that if its the cheapest available energy.

Also, wind tends to be higher at night-time, which makes them a good complement to solar. Getting to >50% is something that many many many people have doubted is possible at all.