Sineng Electric's 50 MW/100 MWh sodium-ion battery energy storage system (BESS) project in China's Hubei province is the first phase of a larger plan that will eventually reach 100 MW/200 MWh. The initial capacity has already been connected to the grid and can power around 12,000 households for an entire day.
Depends on how close they can be made in watt-hours per kilo. They might be good enough for vehicles once the technology comes into reasonably widespread use, while avoiding a lot of the issues with trying to acquire sufficient lithium.