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System Earthing


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Seems like some knowledgeable folks here, so here goes...my first question. I am setting up a new grid-assisted system using a MPP SOLAR - AXPERT - SYRIO VM III 5kW Inverter, and the manual states:

"WARNING: Because this inverter is non-isolated, only three types of PV modules are acceptable: : single crystalline, poly crystalline with class A rated and CIGS modules.
To avoid any malfunction, do not connect any PV modules with possible current leakage to the inverter. For example, grounded PV modules will cause current leakage to the inverter. When using CIGS modules, please be sure NO grounding."

However, the manual for my solar panels, BENQ 320W, says:

"To achieve optimal system performance, it is recommended to ground the negative (or
positive according to model) pole of the solar photovoltaic system array. Failure to correctly ground the system
will lower system performance and void the AUO Photovoltaic Module's limited warranty on
output."

BUT, I found these recommendations in "Bonding and Grounding PV Systems _ IAEI News magazine.htm"

"a large percentage of new inverters being installed today have non-isolated ac output circuits. What this means is that the ac output of the inverter does not pass through an isolation transformer the way most grounded dc inverters do. PV systems with grounded dc PV arrays must have an isolation transformer to isolate the grounded dc array from the grounded ac service conductors that it is connected to on the output of the inverter. With a non-isolated inverter, the lack of isolation to the grounded ac service conductors requires that the dc PV array be ungrounded for the inverter to work. While this type of system is operating, the dc PV array actually becomes referenced to ground through the ac output conductors. The PV industry often refers to this system configuration as “ungrounded,” but in reality the PV array is only ungrounded when the inverter is not operating. As soon as the inverter begins producing power, the whole system becomes referenced to ground through the ac service conductors."

So, there seems to be some disagreement whether or not to earth the negative or positive of the solar panel array - but I would give precedence to the Inverter Instructions, and NOT ground either side of the solar panel array. Any agreement, or dissenting opinions here?

AND, I found this sort of odd statement in the installation manual for QCELLS Q.Peak DUO-G5.X :

"Functional Grounding: For installations in tropic regions (between 23.5°N and 23.5°S) with a module of tilt <5°, functional grounding at the negative generator connection on the DC side must be implemented."... WEIRD?

Thanks!

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55 minutes ago, salience said:

"To achieve optimal system performance, it is recommended to ground the negative (or
positive according to model) pole of the solar photovoltaic system array. Failure to correctly ground the system
will lower system performance and void the AUO Photovoltaic Module's limited warranty on
output."

Grounding/earthing is a safety thing. If someone can explain to my how performance can somehow be affected, then please do so...

This is probably just a fine-print legal-protection thing. I'd follow the advice of the inverter maker in this case.

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Certain module types do suffer degradation in performance if not earthed correctly.

I think the two issues are Potential Induced Degradation (PID) and Transparent Conductive Oxide Corrossion (TCO).

The latter is accelerated by moisture and temperature which could explain the Q cells requirement.

Moral of the story is to make sure that your panels and inverters are compatible.    

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I would find it incredible if MPP Solar inverters and their clones were  NOT compatible with the 2 major brands of solar panels available here in Europe, BENQ and QCELLS. I contacted a retailer of the Inverter WKS II 48V 5kVA - a re-brand or clone of MPP with the same installation instructions, a unit approved here in Europe, and they say the inverter and BENQ are definitely compatible and it is not necessary to ground one or the other pole of the PV array. I am assuming that the answer to all this is contained in the paragraph I posted above about non-isolated inverters:

With a non-isolated inverter, the lack of isolation to the grounded ac service conductors requires that the dc PV array be ungrounded for the inverter to work. While this type of system is operating, the dc PV array actually becomes referenced to ground through the ac output conductors. The PV industry often refers to this system configuration as “ungrounded,” but in reality the PV array is only ungrounded when the inverter is not operating. As soon as the inverter begins producing power, the whole system becomes referenced to ground through the ac service conductors."

It seems then that the instruction sheet for  the BENQ panels assumes that they will be connected to an isolated inverter, and therefore one or the other pole must be grounded. I've not found a contact to write BENQ about this - their instruction manual should be changed to reflect the situation of there being both types of inverter on the market.

SO, has anyone here who is using an MPP / Axpert / etc. inverter grounded a power output pole of their PV array?

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  • 1 year later...

I know this is almost 2 years old now but hoping someone on this thread has come to a conclusion here.

I have the exact same situation as OP and have come up empty with my Google foo.

I have contacted MPPSolar and they simply state what is in the manual.

I am currently not grounding either of the PV conductors or the PV frame.  There is a potential between the frame and Earth I can feel when touching it.  I measured it but do not recall what I found.

My question is, I know I shouldnt ground (to Earth) either of the conductors of the PV because the inverter does not isolate the PV from the output line voltage

-BUT-

Can I ground (to Earth) the framing on the panels?  I am concerned with the safety of the system if it is not grounded.

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  • 2 weeks later...
On 2021/01/26 at 7:18 AM, Lynoise said:

I know this is almost 2 years old now but hoping someone on this thread has come to a conclusion here.

I have the exact same situation as OP and have come up empty with my Google foo.

I have contacted MPPSolar and they simply state what is in the manual.

I am currently not grounding either of the PV conductors or the PV frame.  There is a potential between the frame and Earth I can feel when touching it.  I measured it but do not recall what I found.

My question is, I know I shouldnt ground (to Earth) either of the conductors of the PV because the inverter does not isolate the PV from the output line voltage

-BUT-

Can I ground (to Earth) the framing on the panels?  I am concerned with the safety of the system if it is not grounded.

@Lynoise, did reach any conclusion with the earthing of the frame?

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  • 9 months later...

@Lynoise I have the same issue as you I think. I was washing the panels while they were turned on and I could feel a buzz from the panel frames. I measured it and it was ~40V AC between the frame and earth.

My inverter manual has the statement "Because this inverter is non-isolated, only three types of PV modules are acceptable: single crystalline, poly crystalline with class A-rated and CIGS modules. To avoid any malfunction, do not connect any PV modules with possible current leakage to the inverter. For example, grounded PV modules will cause current leakage to the inverter. When using CIGS modules, please be sure NO grounding"

The system has been working well and producing plenty of power. I have no interest in grounding the positive or negative terminals of the array, but should I ground the frames? If so, should I simply connect them to the same ground as the house or to their own seperate ground?

I've been on google and forums now for hours trying to figure this out. 

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