Battery storage (and battery backup) offers you flexibility with your energy use, and goes very well with a solar system. If you add a battery to your solar, you will be able to keep using the energy generated during power outtages when others who have solar-only systems won't have power. Additionally, battery storage allows you to store your excess solar energy produced during the day to use during the evening when the rates are typically at their highest (4pm to 9pm). Battery storage can be set to recharge with energy during the night when rates are their lowest.

You can read more about Tesla Powerwall here.