For long term (like seasonal) variations in wind/solar output, you're probably not going to be building enough batteries to bridge that gap, so to stick with just wind/solar you would need to either overbuild (perhaps massively) your generation capacity, or build a global grid.
A global grid introduces geopolitical risks (your neighbor becomes not-so friendly and cuts the link when you don't have sufficient generation), whereas massive overbuilding would be expensive. Having some nuclear plants may be cheaper route.
I don't know how many batteries it would take to make up for the losses. I suspect we will have gas and nuclear plants for a long while yet.
Maybe you have data on:
- total installed storage capacity as percentage of daily electricity usage (preferably 95th-percentile daily usage). Hopefully this percentage increases every year.
- how often should we expect to replace batteries. Wikipedia says 400-1200 cycles. Does this mean that whole world storage capacity must be replaced every 400-1200 days?
And it's the same with the turbines and all the rare earths that need to be mined to make the current most efficient dynamos.
If people want to promote wind turbines and solar, they should at least compare like for like, which includes the costs of digging the materials out of the ground, and the disposal of old panels and turbines, in the same way people say 'but nuclear waste!'.
Now, people will say "bUT tHe sUn dOeSn'T sHiNe aT NiGhT", and that's true for the moment. Right now, we cannot shift everything to solar and wind. But if you pay attention to battery development, you don't need to be Einstein to see that pretty soon, we will be able to cost-efficiently store large amounts of energy, distribute it and use it in a way which will solve this intermittency problem.
You can look at the data and read more about this here: https://ourworldindata.org/cheap-renewables-growth