Thanks for the links, sand sounds interesting. I believe gravity batteries outside of pumped hydro just need too much "structure" to store energy and then just have too little capacity. Unfortunately there is sometimes a little bit too much hype about cool ideas that don't pan out. There is also an idea I think for an electric train / rail cars full of ballast being driven up a rail on a hill and then moving down to release electricity. Just a lot of effort.

And yeah thermal batteries should solve one of the biggest consumers, heating. Lots of possibilities. Molten salt works also. I think if you just use water to store heat for the winter you need about the size of a big Olympic swimming pool under your house. But with wind instead of solar you don't even need to store that much.

An important thing I believe is that we have nearly unlimited access to energy with solar and wind turbines / kite power. It requires massive production efforts but you can extract so much energy from sunshine that efficiencies of batteries aren't even that important. Just that you can use cheap and sustainable materials, can recycle them, and can have enough energy density.

So the possibilities are definitely there, but we really neglected to push R&D and massively fund multiple startups for each technology. And we need to suspend patents or drastically shorten their lifespan to like 4 years or so.