I have two solar panels, same brand same model and same voltage and current characteristics. I wish to connect them in parallel. Must I use an external diode? I have checked, they have two diodes within the electrical terminal box.
If they already have diodes in their junction boxes behind both panels then you dont need to add diodes to them. Also make sure the diodes in their terminal boxes are the same so as to ensure their electronic characteristics also match and one panel isn't taking too much load than the other.