A stand-alone PV system that has no back-up generating source. May or may not include storage batteries. Most battery systems are designed for a certain minimum "days of autonomy" - which means that the batteries can supply sufficient power with no sunlight to charge the batteries. This varies from 3-5 days in the sunbelt, to 5 to 10 days elsewhere.
A stand-alone power system that has no Utility connection. Most systems are designed for 3 to 5 days of power from batteries without recharging from a solar source or standby generator.
In mathematics, an autonomous system or autonomous differential equation is a system of ordinary differential equations which does not depend on the independent variable.