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An autonomous system is a stand-alone PV system that has no back-up generating source. May or may not include storage batteries.

Electricity is typically generated by one or more of the following methods:

Storage is typically implemented as a battery bank, but other solutions exist including fuel cells. Power drawn directly from the battery will be direct current extra low voltage (DC ELV), and this is used especially for lighting as well as for DC appliances. An inverter is used to generate AC low voltage, which more typical appliances can be used with.

Autonomous System

Autonomous System

A typical autonomous system of solar PV  at a sewage treatment plant in Santuari de Lluc, Spain

Stand-alone photovoltaic power systems are independent of the utility grid and may use solar panels only or may be used in conjunction with a diesel generator, a wind turbine or batteries.[1][2

Types[edit]

The two types of stand-alone photovoltaic power systems are direct-coupled system without batteries and stand alone system with batteries.

Direct-coupled system[edit]

The basic model of a direct coupled system consists of a solar panel connected directly to a dc load. As there are no battery banks in this setup, energy is not stored and hence it is capable of powering common appliances like fans, pumps etc. only during the day.MPPTs are generally used to efficiently utilize the Sun’s energy especially for electrical loads like positive-displacement water pumps. Impedance matching is also considered as a design criterion in direct-coupled systems.[1][3]

Stand alone system with batteries[edit]

Schematic of a stand-alone PV system with