This entirely depends upon your electricity usage, roof size and geographical location. But, in general, for an average household, a 6.66 kW system is sufficient to cover most of the energy consumption. This will cover approximately $450 per quarter.
A grid-connected solar power system is an electrical power station that uses direct current (DC) electricity from solar panels to supply power within the utility lines of an existing electrical grid. Such systems can feed excess generated energy back into the grid, which is particularly important with renewable energy generation.
Your solar system will shut down if there is a power outage. This is a safety precaution because a grid-connected solar power system sends solar power to the grid, and it becomes dangerous for linesmen working on any repairs or maintenance. Hence, it turns off and will automatically turn on when the power comes back during daylight hours.