Large scale storage is not cost effective with current tech. It is not just a civic engineering problem.
Solar power is very cheap, but a complete 24/7 solution requires batteries. Those are much more expensive than the panels. A better battery is all we need. Panels are good enough already.
The overwhelming majority of storage used will not be batteries, unless some new chemistry's cost is very low.
Large-scale storage will be very cheap, on par with panels. It really is just civil engineering. Any competent civil engineer can sketch a practical, cheap storage system using only century-old tech.
Hand-wringing over utility-scale storage amounts to concern trolling.
Not the person you're replying to but pumped hydro is the most primitive I know of.
Also: why must the highly variable renewables share the grid with highly variable demand, use them to make hydrogen (only when the sun is shining/wind is blowing), feed that into a totally separate power plant, simple to manage - if renewables really get cheap who cares if it's inefficient.
Hydrogen will be one storage medium, mostly stored underground where geology favors it. Tanked anhydrous ammonia will be common, with more ordered from tropical solar farms when local tankage runs low. Underground and underwater compressed air will also be common. Liquified air might be.
Not the OP but dams and resevoirs is what he is talking about, I assume. Pump water uphill while the sun is out, let it feed back downhill and generate power overnight. It is century old stuff and it is very much validated to work.
Solar power is very cheap, but a complete 24/7 solution requires batteries. Those are much more expensive than the panels. A better battery is all we need. Panels are good enough already.