> It's rare for there to be little wind in the North Sea. It's only a couple days a month when it's below 1/3 capacity.

The expected load factor for offshore wind power is around 50%. Much better than onshore wind (~35%) but still far from perfect. You can compensate some part of it by installing more power than what you need, but then you must pay for the unused capacity (£1.5B paid last year).

> And it's negatively correlated with solar: a day that's both cloudy and low-wind is very rare.

A day maybe, but in winter night last up to 16 hours. And wind droughts can last more than two weeks.

> But it does happen, so you need backups. The good news is that natural gas backup generators are fairly cheap per peak megawatt

But they have limited flexibility: you can't turn it on and off easily and there's limited power modulation you can do. That's why France keeps its gas output relatively constant in winter and do the modulation with nuclear despite its marginal cost being lower than gas on paper.

Renewable are an important leverage to reduce greenhouse gas emissions, but they are also really challenging to work with, far from the simplistic view people can have on the internet.