As others have said, pumped storage is dependant on geography but it’s great where available. I have high hopes for compressed CO2 storage or molten salt storage. Flow batteries are promising as well, there’s just so many emerging technologies it’s hard to keep track of them all but I’m rooting for the ones that use abundant cheap materials that can retrofit into existing retired coal plants. If you stick a molten salt core where a coal plant was it can heat steam for the existing turbines and substation and transmission infrastructure.