For the US PJM (US east coast and midwest) and CAISO (California, Oregon, Washington, Nevada) grid areas, total wind power fluctuates over a 4:1 range on a daily basis. Both grids post dashboards where you can see this. Averaging out wind over a large area does not help all that much.
This largely means we have to build a bit more of each, and store some.
The chances of an entire continent being devoid of wind and solar for an extended period becomes vanishingly small pretty fast.
This needs a better cite.
Someone claiming, there was a day with no wind and no sun in whole north america in the last 30 years?
I wouldn't believe that. But concrete data to have, is of course better than assuming ..
It just doesn't "average out" across even a sizable country.
[1] https://www.caiso.com/todays-outlook/supply
[2] https://dataviewer.pjm.com/dataviewer/pages/public/wind.jsf
It goes dramatically up and down on a daily pattern, too.
...or we can just build nuclear powerplants, no need for millions of batteries, power at night too, and all it takes is removing a few "greens" from their position of power.
And we do have and build much more high voltage transmission lines.
And otherwise there is no technical limit to build lots of rare earth free batteries. Once they are common in allmost every household and once electric cars can be used for that, too, I don't see any technical problem.
It takes time and investment of course. And pragmatism till we are there. I don't like coal plants, but I am not in favor of just shutting them down now.