For solar and wind you need to store energy when it's not sunny or windy. You don't care much about energy density for a stationary battery bank. Solar is already the cheapest way the generate energy even when you include the cost of batteries, sodium batteries just make that even cheaper. That's huge massive improvement for the energy grid. And that saves lithium for where you need higher energy density.
Solar filling up large sodium batteries, sodium batteries filling up the lithium batteries in you phone and car. That's the future.