24 / 48V switch from solar panels to the national network

This type of home system was designed not to transfer excess energy to the national grid, but to close the circle of our project, we must also consider the possibility that the charge controller disconnects the batteries in the event of low voltage: for example, in the winter when the days without sun exceed the normal days, to avoid finding ourselves without energy. 

One solution can be to install a changeover switch that allows automatically divert the current withdrawal which passes through or from batteries, or from the external grid. This function allows disconnect the batteries when they are flat, therefore the external grid will be used. When the photovoltaic group has restored its ability to supply energy, the switch will disconnect the electricity is taken externally. For more details see Figure 1 below.

Figure 1

Note: remind, the energy is never fed into the electricity grid, but is only withdrawn when needed.

The charge controller, beyond the functions of controlling charge/discharge of the batteries, is also used to automatically control the switching between the inverter and the external electrical grid, the output of the controller (marked with light bulb symbol) is present a voltage which is capable of keeping energize the relay coil of the switch till when the voltage battery will be insufficient, if, on the other hand, it falls below a predetermined value, the charge controller cuts the voltage at the output terminals by deactivating the commutator coil, generating the deviation of the current drawing from batteries to the external power supply. For more details see Figure 2 below.

Figure 2

Figure 3 below shows when the charge controller receives energy from the batteries

Figure3

Figure 4 below shows when the charge controller will not receive energy from the batteries (supply from the electrical network)

 Figure 4

 Figure 5 below shows the complete drawing

Figure 5

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