The development of storage has a long way to go. Outside batteries, there are other options, such as pumped storage. Even then, battery prices might go down enough to make other forms of storage uneconomic.
I also predict that a revolution is yet to happen in the transport of energy. For those areas that can't be self-sufficient in solar/wind, it may turn out to be cheaper to capture renewable energy elsewhere then transport it to where it needs to be used (we already do that with fossil fuels).
[1] https://www.sciencedirect.com/science/article/pii/S136403212...
I asked Claude:
"If combined wind+solar output drops to ~10% of nameplate during one of these (a standard threshold), a ~77 GW fleet sized to meet average winter demand produces ~7.7 GW against a ~22 GW cold-snap peak — a 14 GW shortfall that storage alone has to cover. That works out to roughly 340 GWh for a 1-day lull, ~1 TWh for 3 days, ~1.7 TWh for 5 days, ~2.4 TWh for a week, and ~3.4 TWh for 10 days. Ontario's entire current and under-construction battery fleet sits in the single-digit GWh range, so even a mild 3-day lull needs ~100-200x what's actually being built, and a serious week-plus event needs 400-600x — which is why lithium-ion batteries work fine for hourly duration but make no economic sense at the multi-day scale these lulls demand."
Battery storage for diurnal variation in favorable locations looks feasible, battery storage for annual variation looks absurd. Maybe you can overbuild solar by a 3x factor in some places, I've gotten cost numbers from 'a little less than what an AP1000 is claimed to cost' to 2x more with back of the envelope calculations that probably aren't worth anything. Then there's Dunkelflaute.
It would help if you could find a good use for the excess energy but the capital cost of anything you don't use all the time is multiplied.