If you're worried about power outages batteries can be a great solution to give you power throughout a power outage. With solar they get recharged by the sun during the day, and ready to last through the night until the next sunrise to recharge again. This gives you perpetual power off grid. Some regions like in California may also need batteries to help send power back to the grid in the evening time. It's important to note that most modern solar systems don't require batteries at the same time as the solar installation.