Has a grid-scale battery been invented?
The intermittency of wind and solar power is its great weakness. Matching supply and demand is little more than luck. Only if "renewable" energy could be stored would it be much more than a curiosity. But devising a big enough storage battery has stumped everyone so far.
But there is a technology that could in theory do the job and some keen beans have been working on it for 13 years now. See the video below. And it has been ready for use "soon" for a while. They even have a demonstration plant running so could it all happen soon?
We will see I guess, but the technology looks like being tricky stuff. It uses liquid air and temperatures have to be close to zero degrees Kelvin for air to liquefy. But liquid nitrogen is already used widely for a variety of purposes so where's the problem?
The problem seems to be managing the temperatures used. The liquid seems to "go off" rather rapidly when you do things with it. So your stored air loses a lot of its usability after 24 hours. It is only a short-term battery. It steadily goes "flat" without recharging. So that is a large limitation. It's not a lot better than windmills and solar panels
So the Holy Grail of hi-tech energy storage has still to be reached.
But does it really matter? The LORD has given us something that will store all the energy you want for as long as you want it -- using no technology at all: a lump of coal.