The following block diagram illustrates the different stages of the system, let's try to understand them stage by stage:
The two power input sources are the solar panel and the AC/DC charger units. The AC/DC charger system remains active all the time as long as the utility mains is available.
The solar panel also supplies the required voltage, however its output varies depending upon the intensity of the sun rays over it, which becomes zero after dusk.
The above two power inputs are simultaneously fed to the AC/Solar changeover circuit which gives first preference to the solar energy and switches its power to the next stage as long as its above the required level.
The moment the solar voltage drops below the lower threshold, the changeover relay switches the AC/DC charger to the next stage.
The above DC power is fed to an MPPT charger controller circuit, which effectively conditions the voltages such that it becomes safely suitable for charging the battery positioned in the next stage of the system.
The MPPT monitors the charging conditions and cuts off power to it once it gets optimally charged.
The DC from the battery has to go via a low voltage detector stage whose duty is to check the battery voltage level and stop it from reaching the next once the low voltage threshold is reached.
The DC from the Battery after passing through the above low voltage detector stage feeds to a DC/AC inverter whose function is to transform the battery DC into 220V or 120V AC as per the particular country specs.
The inverter functioning is controlled by the next stage which is yet another DC/AC relay changeover circuit. This stage switches the inverter ON and transfers its AC power to the appliances only during the absence of utility mains input AC.
For so long the utility mains is present, the changeover relay circuit keeps the battery disconnected from the inverter and keeps the utility mains AC connected with the appliances. The moment utility mains fails, the above connections are reversed so that the appliances instantly start operating via the inverter AC output.