This type of system is not connected to the utility grid, instead a battery bank or storage devices to store the solar power. In an off-grid system, the battery is charged through a charge controller/MPPT (Maximum Power Point Tracker) circuitry. The energy stored in the battery is fed to the inverter which in turn feeds the AC load. Thus, an off grid PV system can deliver power even during night with a condition that the battery has enough stored power. So, the system designed should be in such a way that it handles the peak load when the PV array is not able to produce that much amount of power ensuring that there will be continuous supply of power. This is called autonomy of the off grid system, and usually off grid systems are designed for 2 or 3 days autonomy backup, i.e. over sizing of the battery bank and Solar PV system to ensure enough power is available even when there is a week of over cloudy and hazy daylight. (monsoon & winters in India)