Types of Systems: Residential AC / Genset System
A residential  system will usually have a sizable PV array  and battery bank, one or two inverters, and a backup generator. The inclusion of a generator allows for battery charging during long cloudy periods. A gasoline, propane or diesel generator combined with a battery charger can supply power when the PV array falls short. If the PV array is sized for average conditions, then during extended overcast situations or periods of increased load, if the battery state-of-charge becomes low, the generator can be started. The generator will power the AC loads in the house and the inverter’s battery charger to fill the batteries. Sizing the PV array large enough for worst case  weather conditions (making a generator unnecessary) will almost always be cost prohibitive. Array, generator, and battery bank size must be chosen carefully for reliable system operation.