The grounding of installations with photovoltaic panels is one of the most controversial aspects due, generally, to the absence of specific technical regulations for this type of project. Grounding comprises both the earthing of equipment (protective earth) and the earthing of an active conductor (system earth).
Photovoltaic system grounding
When deciding to ground exposed metal parts (as protection against storms, indirect contact, etc.) there are certain important aspects that the installer should bear in mind:
The photovoltaic solar modules have a specific hole (hole) in the frame for earthing (generally indicated by the earth symbol ), as shown in the picture.
Grounding holes for solar panels
As we say, the grounding is done through those holes in the frame because, generally, the frames are made of anodized aluminum, which is a surface treatment that is applied to the aluminum frame and makes it behave as a relatively good insulator.
Therefore, the connection of the protective earth conductor in another hole would not be advisable, it should be done in the one indicated with the electrical earth symbol.
In addition to this, to ensure good electrical contact, it is recommended to use a stainless steel connection terminal.
However, for electrical purposes, despite what has been said about the aluminium surface treatment, the frame of a solar panel should be considered as an exposed metal part.
It is recommended that the protective earth conductor should not be screwed directly to the frame of the panels, but rather by means of an auxiliary terminal, so that a module can be removed (due to a fault, maintenance, etc.) without interrupting the earth connection of the rest of the installation.
Simply connecting the module frames to a grounded structure is not considered to be effective grounding. 
Very common error.
The protective earth conductor of the solar modules should also be connected to a point on the structure.
The protective conductors must be connected to the grounding point of the installation, which in turn will be connected to the main grounding electrode (usually of the spike or javelin type) through the connecting conductor.
The sections of the protection and bonding conductors and the characteristics of the earth electrodes (dimensions, connections, etc.) shall comply with the corresponding RBT low voltage electrotechnical regulations.
The grounding conductor of the photovoltaic system must be bare, or protected under a pipe.
Example of earthing of solar panels and structure
We must take into consideration the importance of a good grounding in a photovoltaic system with solar panels, because in a system with metal masses isolated from the ground, a defect such as the contact of an active conductor with the frame of a solar module, goes almost unnoticed.
However, it has been proven that such a defect leads to the appearance of a similar one within a short period of time. These two faults can lead to the short-circuiting of several panels in series (through the protective conductor, for example) and a drastic reduction in the voltage of the entire row.
For this reason, in some countries such as the United States, it is obligatory to detect this short circuit situation when the photovoltaic installation is located on a roof. The most commonly used protection scheme is the earthing of the metal parts of the field, the earthing of the negative and the use of a fault current detector.
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