The majority of solar installations are grid tied. Grid-tied solar systems will use the grid to export power during the day and import power at night. These systems have financial and environmental benefits but they will turn off if the power goes out. In order to have power during an outage, you would need to have a battery with your solar. 

In most cases, once you add batteries to a solar system, it becomes more a luxury item offering backup power and increased self-reliance over financial benefits.