I am looking for help

System

Dear all I am beginner in solar energy systems, but I am well familiar with energy issue

I am looking for automatic switch AC power supply that will exchange source of energy to my house in case the battery voltage is going down

the two source of energy are

1- the electric net

2- AC power or DC power from the battery that will be charged by the panel solar


I am looking for switch that will exchange the source fast without effecting the load

i,e, I will not see and power cut off

Thank you