Solar question

For what its worth, your Renogy kit does not come with a transfer switch, so most likely is that the tech that installed the unit ran power from the inverter to the portions of the system you now have power to them, and eliminated the connection to the shore power to those circuits.
If you want the ability to select power source, both Lowes and Home depot sell transfer switch units and kits, basic 30 amp unit would run about $100 - $150 plus installation.