One big electricity storage problem is seasonal - eg cold sunless winters. Eg batteries are great for daytime charging your car - but they aren't great for storing up a whole summer's worth of energy to burn in the winter. Hydrogen could do that.
A 3x overbuild of solar+wind in an optimal mix, along with a continental grid and 3 hours worth of batteries is all you need for 99.99% reliability over an entire year.
I would assume that many/most countries in climates where power interruptions quickly turn into deaths to avoid building in a dependence on an extra-territorial grid for base-level power supply.
It's already a problem in Eurasia with nation states using eg. natural gas delivery as a means to apply political pressure on other states, and this while it is still (relatively) easy to solve energy needs as carbohydrates can be easily transported.
If all border crossing energy/power delivery is through a physical network of cables, adapting if delivery is cutoff would be almost impossible unless all gas/coal/oil plants were kept at/near operating condition.
Hence, yes, the buildout must be some X times necessary power, as much as possible locally. A significant fraction of that generated power should be used to create
a) industrial feedstock
b) to generate liquids/gas that can be easily used and transported.
The latter in the case some nation is being pressured by energy blockades where the existing grid can not supply enough energy through transmission lines from other bordering states.
You probably want a 6x overbuild to account for round-trip losses in your storage system. Cost of storage falls very fast as your efficiency requirements are relaxed, which becomes attractive as raw generating cost plummets.
There are plenty of other storage solutions that are cheaper than lithium ion batteries and vastly more efficient than hydrogen. Even just cabling energy around is an option. E.g. the UK is looking at a solution for getting a few GW of Moroccan solar energy connected to their grid to supplement their wind power (which they have throughout the year) and modest amounts of solar which is a bit more seasonal.
The fallacy in your argument is assuming there's a need for seasonal storage. That need would only exist if you rely exclusively on solar energy. Which of course people up north don't tend to do and people closer to the equator could actually feasibly do throughout the year.
Plenty of places get by mostly powered by different combinations of renewables. E.g. Norway (wind, hydro), Iceland (geothermal, wind), Scotland (wind, tidal wave power), etc. without a lot of storage.
Geothermal and Hydro are steady sources, not intermittent, so that’s why you don’t need a lot of storage. The hydro dam is the storage.
Geothermal also isn’t renewable unless used very very sparingly, most installations I know of will deplete the source in a few decades, perhaps a century.
