Quite often in an off grid solar power system, the batteries are charged with solar panels. Sometimes solar power alone may not be enough to charge the battery, in these cases, an AC generator can be used to help keep the battery charged.

An inverter/charger would convert the AC power from the generator to charge the DC battery bank. An off grid inverter/charger would be converting the power in both directions, from AC to DC to charge the battery from the AC generator, and converting the DC power from the battery to AC for your appliances.