But how often is it cloudy and windless for weeks at a time? And for those once-every-few-years scenarios, why shouldn't we build (far cheaper) carbon-captured natural gas peaker plants?

Besides, you've got to keep in mind that we aren't going to be building for yearly-average kWh consumption. Companies will be building overcapacity to take advantage of high-demand/low-supply peak pricing.

I don't think it is unlikely that we'll end up with a situation where PV on an overcast day is enough for "baseload", with the practically-free electricity on sunny/windy days opening up new economic opportunities.

> But how often is it cloudy and windless for weeks at a time?

'“Energy Droughts” in Wind and Solar Can Last Nearly a Week, Research Shows':

* https://www.pnnl.gov/news-media/energy-droughts-wind-and-sol...

See also:

* https://en.wikipedia.org/wiki/Dunkelflaute

I think it would be location-dependent (low risk that (e.g.) the UK would be windless for long stretches of time, especially off the coast).

I agree generally, but is carbon-captured natural gas generation actually a thing? The only carbon capture I've heard of is at the gas production site removing CO2 from the reservoir gas and pumping it back underground - that's not after combustion. (And the pumping it back underground hasn't been particularly successful, eg https://www.boilingcold.com.au/regulator-limits-chevrons-tro... )

If it was only a matter of 'once-every-few-years' then current emergency capacity will suffice. The problem is that:

A) It happens often enough to be a problem emergency capacity can't handle.

B) Natural gas is not always an option (especially when Russia is the only readily available seller in the area and you DON'T want to be dependent on a potentially hostile neighbor).

C) Existing storage solutions require a massive investment in local solutions, or in the national grid if storage is centralized.

We need to re-think the entire idea about energy always being cheap and available, while somehow preventing those with more money from simply monopolizing supply by outbidding everyone else. You won't solve that with batteries. Many therefore try to maintain the current situation by doing this the old way.