Yes, absolutely colossal amounts of batteries though - what if it’s quite hot but also cloudy for 5 days in a row?

You either have to significantly oversize the PV (easier said than done, when its energy density is already not that high per m2), or have enough batteries to last for multiple days of full load. If you do the maths that’s a lot of batteries

>what if it’s quite hot but also cloudy for 5 days in a row?

The main idea is to then import power from somewhere sunny and/or windy or mountainous, using money you saved when they had the rain and you had the sun.

Batteries and other storage mechanisms will gradually reduce the need for doing so, but aiming to entirely eliminate all need for cooperation with others seems a bit paranoid.