None of this is intended to provide a consistent source of electricity. They're intended to fill in the gaps from uneven renewable energy production or other disruptions. Apparently, it's been working very well in Southern Australia.
Thermal storage is a promising solution because it will likely end up being considerably cheaper than batteries. The most promising type is salt storage for concentrated solar plants. They can potentially store enough heat energy to maintain consistent output all night long. Wind doesn't get that same deal - currently unused Wind power can only be stored as electricity.
Like pumping a bunch of water up high, or spinning a big ass flywheel.
I understand a flywheel might not be realistic at these scales, but water pumping seems like it could scale stupidly high.