Two to four mounting brackets per panel is standard for most systems. For portrait orientation, panels are usually mounted with two rails, with one bracket at each rail end (total of four brackets).
These mounting holes are typically located in the frame on the back or sides of the panel, not on the glass or the back sheet itself. By utilizing these pre-drilled holes, the installation system can safely anchor the solar panels without damaging the internal components.
The AC output terminals of the inverter supply the Neutral to Ground connection, and no secondary grounding connections are permitted. See also: Connect A Solar Panel To An Inverter (Here's How).