RSP

The way I understand is that the panels should be earthed on the frame only.The negative and positive from the panel(s) are isolated from earth.The DC from the panels through the electronics couples to the AC without any galvanic ie no transformer in the circuit .If you ground either the + or - of the PV panels the result will be a short circuit in the inverter and cause damage .The PV panels therefore should have no leakage current between the + or - to the frame .This is the reason why the manufacturer stated no leakage from the panel to the frame.Trust that this makes sense