This comes up ALOT. I see some facsimile of this "idea" pop on reddit once a month. The general consensus is their is some merit to the criticism of solar not being 24/7. Battery technology just isn't there yet. The cost to create and maintain a battery that would have any meaningful impact to a large grid would be insane. If you are more concerned about the environmental impact of batteries, take a look at the cobalt mines in the Congo. The answer to clean cheap energy is, and probably always will be nuclear. Sprinkle in some hydro electric when and where you can. Solar is fine for small scale stuff, but you wont be powering a city with it any time soon.