@Air And it's incorrect. They don't have to be country-sized, unless the speaker does some shifty sophistry by changing which country they're referring to, halfway through the sentence. See the calcs I do above: to power the UK would need wind on less than 10% of the UK. "< 10% of the UK" is not "country-sized" if that country is the UK. "substantial fraction" is a bit of weasel-wording because it can mean pretty much whatever one wants it to mean.

@Air MacKay's message is that we can't do it with renewables alone. That's not actually a true message. So I don't consider it a valuable message. If one's guerilla physics leads one to the wrong conclusion, then it's the guerilla physics - not reality - that's wrong.

@EnergyNumbers: Just one thing: what about windless, cloudy days? What kind of energy would be powering the country then? Can you give some rough numbers on what storage facilities would carry the country through 48h of dense fog weather?

@SF. Here's one way to do it, for Britain: energynumbers.info/balancing/?cy=gb&example=1

That's based on about 5 years of real data. There are lots of ways to do it - that particular scenario has no tidal, no biomass, low guaranteed interconnector capacity, very few varieties of storage.

@EnergyNumbers: 400000 GWh store of P2G CCGT means storing 10 million tons of liquid hydrogen and roughly second that much of liquid oxygen.

@SF. Or methane. Which we already know how to do. We've done it for decades, and it's easy. We know how to manage it, ship it, and generate electricity from it. Its storage is cheap and scalable.

@Ethan48 I would argue that EE.SE (rather than Eng-Tips) is the nearest benchmark.