We do not yet have effective and economical means of storing energy in grid scale quantities that are readily deployable near where that power is consumed.
It's a huge problem actually, the biggest one facing renewables like solar.
This is a problem I'd very much like governments to sink a bit of money into. Sure, we don't have 100% efficient energy storage, but we certainly have technology that does the job. Liquid air energy storage, fly wheels, thermal sand batteries etc, can be installed anywhere and are available right now. Not to mention pumped hydro if you have suitable terrain.
There's a lot of stuff that we could build, and honestly, we just need to build it, now, even if it's not profitable, or super efficient. There's a bunch of solar and wind around the world not being built, or curtailed because prices go negative when there's no one to store it.
The free market sucks. We need government intervention to do the things the profit motive won't.
but we certainly have technology that does the job.
Absolutely not if we're talking about nation-wide energy storage. The world's largest STEP, Hongrin-Leman, Switzerland, which occupies a considerable amount of space, has only a capacity of 100 GWh, which represents less than 1h15 of the winter night consumption of a country like France which consumes 70 GW at that time.
It would take 10 to sustain one night without wind, as you can have several each year. Then we would have to fill them entirely in one day for the next night which is impossible.
And that's just for the problem of capacity, such a STEP generates less than 500MW of power, so it would actually take 140 STEPs of that size to provide enough power.
And we're talking about today, where most cars and heating are still fossil-fueled and need to be replaced by electric.
Unless you find a technology that is now a miracle, running a country on solar and wind without hydro-electricity or nuclear is science fiction.