So if your relay fails? We do the bond from the N load of the inverter to earth.

Why would the relay fail? It is switching no load, unless something has gone terribly wrong.

From a random hager contactor datasheet (using a contactor as worst case, relays have 10x the mechanical operations):

Since their is no electrical load, we use the mechanical endurance. Say you get load-shed 5 times a day:

100000/5 = 20000 days = 54.79 years

If you take the 30000 number you get 16.44 years.

If you have an concern that the relay may fail, just use the normally close contact. Even if the coil fails the relay contact will stay in the closed position. This will create a permanent bond even when Eskom is on until you can replace the relay.

 

I think what @Engel meant is what if the internal bond relay of the Growatt 5000 ES fails.

So I know a lot of people have been debating about E/N bonding and a lot of people are for a permanent bond based on the fact that a contactor / relay can fail.

 

However, I saw this: https://ecasa.co.za/technical/neutral-earth-bonding-clarified/

 

Contactor / relay is the way to go still.

3 hours ago, PsyCLown said:

So I know a lot of people have been debating about E/N bonding and a lot of people are for a permanent bond based on the fact that a contactor / relay can fail.

 

However, I saw this: https://ecasa.co.za/technical/neutral-earth-bonding-clarified/

 

Contactor / relay is the way to go still.

Do we see many revoked CoC's in the near future? 🤨

Second to that who is paying for the upgrades ?? The horse left the barn way before there as a line in the sand. 

 

Albeit with the Sans regs and how I read it I did relays, however had to CoC properties sold that had a perm bridge and other forums AiA have stated to use a perm wire. 

It's like a religion this industry, one side or the other haha.

If one is worried about contactor failure or malfunction, what about running a 125VAC rated (or 220VAC to be safe) alarm/light buzzer across PE and N. If the voltage rises/drifts, the alarm sounds.

Label below could read "stop using the inverter and call an electrician if the alarm is sounding."

I have tested a 220VAC unit on a Variac and it starts making noises from 3V till 220V, changing pitch, frequency and volume as the voltage rises.

We have been around the block so many times regarding permanent neutral earth bonding. It is not allowed and is dangerous. A TN-S system shall not be converted to a TN-C system and all installations done with permanent neutral/earth bond is not compliant and any COC that was issued for such installation is not valid. The electrical code is clear on this no reason for powers to be to debate the issue. The ECB is following up on IE's and MIE's issuing COC's knowing that permanent bond exist in the installation.

6.4 Neutral earthing
7.16.4.1 Whereas TN-C systems may be implemented along the distribution
system backbone, the individual service connections at every distribution
kiosk shall be TN-S.
7.16.4.2 From the point of supply to each user or part of a communal
installation, the neutral and earth conductors shall be separate conductors.
7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
shall be fitted to the outside of each distribution kiosk in the distribution
system, indicating “Neutral earthed inside”.
7.16.4.4 A clear notice shall be fitted at the combined neutral-earth
connection inside each distribution kiosk in the distribution system, that
prohibits the removal of this connection while the supply is alive, or might
become alive.
7.16.4.5 The neutral shall not be earthed beyond any earth leakage unit.
7.16.4.6 A TN-S system shall not be converted to a TN-C system.

11 minutes ago, TaliaB said:

We have been around the block so many times regarding permanent neutral earth bonding. It is not allowed and is dangerous. A TN-S system shall not be converted to a TN-C system and all installations done with permanent neutral/earth bond is not compliant and any COC that was issued for such installation is not valid. The electrical code is clear on this no reason for powers to be to debate the issue. The ECB is following up on IE's and MIE's issuing COC's knowing that permanent bond exist in the installation.

6.4 Neutral earthing
7.16.4.1 Whereas TN-C systems may be implemented along the distribution
system backbone, the individual service connections at every distribution
kiosk shall be TN-S.
7.16.4.2 From the point of supply to each user or part of a communal
installation, the neutral and earth conductors shall be separate conductors.
7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
shall be fitted to the outside of each distribution kiosk in the distribution
system, indicating “Neutral earthed inside”.
7.16.4.4 A clear notice shall be fitted at the combined neutral-earth
connection inside each distribution kiosk in the distribution system, that
prohibits the removal of this connection while the supply is alive, or might
become alive.
7.16.4.5 The neutral shall not be earthed beyond any earth leakage unit.
7.16.4.6 A TN-S system shall not be converted to a TN-C system.

@TaliaB For any new readers can you perhaps provide 3 pictures of the TN-C, TN-S and TN-C-S connections. Then all the info is at 1 place. 🤔

Edited January 23, 20242 yr by Scorp007

40 minutes ago, Scorp007 said:

@TaliaB For any new readers can you perhaps provide 3 pictures of the TN-C, TN-S and TN-C-S connections. Then all the info is at 1 place. 🤔

 

TNC- Least safe 

TNC-S- Safe

TNS- Safest

TT- Safe 

IT-Less Safe

 

Edited January 23, 20242 yr by TaliaB

19 minutes ago, TaliaB said:

 

TNC- Least safe 

TNC-S- Safe

TNS- Safest

TT- Safe 

IT-Less Safe

 

Nice👏, but you forgot to mention that some of the farms in Nothern Cape uses SWER lines(Single Wire Earth Return) 😄

SWER distribution lines are used extensively in remote parts of our country as an economic means to deliver electrical energy to small customer loads, scattered sparsely over vast areas. These SWER systems are normally supplied from very long three-phase distribution feeders. In many areas of Australia, rural electrification systems were established by the State Electricity Boards during the 60s, 70s and 80s under community service initiatives.

@TaliaB  Have been in discussion with Danie Esterhuizen, Vice Chairman at ECASA on the DEYE Whatsapp group.

He maintains that the document actually means that the recommended bonding method indicated is actually a permanent bond and not a relay/contactor and released a video explaining why it is so. 

I have asked them for some clarity so will see what they say 

This is the video he posted explaining the reasons why a hard bond is the way to do it. 

I can't say that I am 100% convinced to be honest but I am not an electrician so he could be speaking Greek!

 

 

Edited February 22, 20242 yr by Sc00bs

On 2024/02/16 at 11:22 AM, Sc00bs said:

@TaliaB  Have been in discussion with Danie Esterhuizen, Vice Chairman at ECASA on the DEYE Whatsapp group.

He maintains that the document actually means that the recommended bonding method indicated is actually a permanent bond and not a relay/contactor and released a video explaining why it is so. 

I have asked them for some clarity so will see what they say 

This is the video he posted explaining the reasons why a hard bond is the way to do it. 

I can't say that I am 100% convinced to be honest but I am not an electrician so he could be speaking Greek!

 

 

Thanks @Sc00bs for sharing. Not really impressed to be honest.

He begins by taking a snipe at electricians for not being able to read, and then proceeds to reference a bonding scenario that is not relevant to solar inverters that are installed in parallel and remotely from the utilities point of E-N bonding (ie the scenario that describes pretty much all domestic Sunsynk/Deye installations and many industrial installs too). Nothing wrong with the SANS regulation itself (alternative supplies tied in at the same location as the utilities E-N bond), it's just not the correct application.

 

The NRS Association has just released a user specification which deals directly with embedded generation in parallel operation with the utility {small-scale embedded generator (SSEG)}. (ie the domestic Deye/Sunsynk/Victron/etc inverter).

Whilst this is not a SANS (South African National Standard), it is a document prepared by a body that represents Eskom and all municipal utilities around South Africa. I'm not sure if it is politics or ineptitude at SANS that has delayed the updating of SANS 10142 to include what is included in this document, but perhaps they are just slower moving in general.

Anyway, you can find a copy of this document here: https://www.sseg.org.za/wp-content/uploads/2024/02/NRS-097-2-1-Published-2024.pdf , quite easy to read (for those semi-literate Electricians remember 😉)

I highly recommend reading it in full, including the Forward that details the entities and persons that wrote the document.

In my opinion it agrees with the bulletin published by ECASA referenced earlier by @PsyCLown about a month ago, (though evidently interpreted differently by others).

Here's an excerpt from the NRS 097-2-1:2024 Edition 3 published earlier this month (red colouring is added for emphasis):

5.4 Neutral to earth bonding when forming an intentional island
5.4.1 To prevent a SSEG neutral connection to the the utility neutral through an earth conductor when the SDU opens, the SSEG shall not have a permanent neutral bonding to earth.
5.4.2 A hybrid system intended to form an intentional island on the load side during utility supply interruption shall open the SDU to prevent unintentional island on the utility side.
5.4.3 Since the SDU opens the neutral on the utility side, the intentional island neutral shall be bonded to earth within 200 ms after the SDU operation using a neutral to earth bonding unit (NEB).
5.4.4 The NEB shall open within a time period of 200 ms before the SDU reconnects the inverter to the utility supply.
5.4.5 The NEB shall consist of an electromechanical switching device rated at the nominal current rating of the inverter.

5.4.6 The total clearance between the inverter neutral and earth conductors when the NEB is switched off, shall be equal the clearance of the SDU in its open state or more.
5.4.7 The NEB shall be an internal inverter component or an external device that is activated by a dedicated control port of the inverter.
5.4.8 The inverter data sheets shall indicate that it contains an internal NEB or a dedicated NEB control port for external devices.
5.4.9 Installation requirement: Inverters equipped with the NEB control port only, shall have external electromechanical NEBs installed that are SANS/IEC 60947-1 and SANS/IEC 60947-4-1 certified.

3 hours ago, WillHza said:

Thanks @Sc00bs for sharing. Not really impressed to be honest.

He begins by taking a snipe at electricians for not being able to read, and then proceeds to reference a bonding scenario that is not relevant to solar inverters that are installed in parallel and remotely from the utilities point of E-N bonding (ie the scenario that describes pretty much all domestic Sunsynk/Deye installations and many industrial installs too). Nothing wrong with the SANS regulation itself (alternative supplies tied in at the same location as the utilities E-N bond), it's just not the correct application.

 

The NRS Association has just released a user specification which deals directly with embedded generation in parallel operation with the utility {small-scale embedded generator (SSEG)}. (ie the domestic Deye/Sunsynk/Victron/etc inverter).

Whilst this is not a SANS (South African National Standard), it is a document prepared by a body that represents Eskom and all municipal utilities around South Africa. I'm not sure if it is politics or ineptitude at SANS that has delayed the updating of SANS 10142 to include what is included in this document, but perhaps they are just slower moving in general.

Anyway, you can find a copy of this document here: https://www.sseg.org.za/wp-content/uploads/2024/02/NRS-097-2-1-Published-2024.pdf , quite easy to read (for those semi-literate Electricians remember 😉)

I highly recommend reading it in full, including the Forward that details the entities and persons that wrote the document.

In my opinion it agrees with the bulletin published by ECASA referenced earlier by @PsyCLown about a month ago, (though evidently interpreted differently by others).

Here's an excerpt from the NRS 097-2-1:2024 Edition 3 published earlier this month (red colouring is added for emphasis):

5.4 Neutral to earth bonding when forming an intentional island
5.4.1 To prevent a SSEG neutral connection to the the utility neutral through an earth conductor when the SDU opens, the SSEG shall not have a permanent neutral bonding to earth.
5.4.2 A hybrid system intended to form an intentional island on the load side during utility supply interruption shall open the SDU to prevent unintentional island on the utility side.
5.4.3 Since the SDU opens the neutral on the utility side, the intentional island neutral shall be bonded to earth within 200 ms after the SDU operation using a neutral to earth bonding unit (NEB).
5.4.4 The NEB shall open within a time period of 200 ms before the SDU reconnects the inverter to the utility supply.
5.4.5 The NEB shall consist of an electromechanical switching device rated at the nominal current rating of the inverter.

5.4.6 The total clearance between the inverter neutral and earth conductors when the NEB is switched off, shall be equal the clearance of the SDU in its open state or more.
5.4.7 The NEB shall be an internal inverter component or an external device that is activated by a dedicated control port of the inverter.
5.4.8 The inverter data sheets shall indicate that it contains an internal NEB or a dedicated NEB control port for external devices.
5.4.9 Installation requirement: Inverters equipped with the NEB control port only, shall have external electromechanical NEBs installed that are SANS/IEC 60947-1 and SANS/IEC 60947-4-1 certified.

Seems in line with what I have read and @TaliaB also indicated before. 

11 hours ago, Scorp007 said:

Seems in line with what I have read and @TaliaB also indicated before. 

@WillHza

I tried to read and understand the doc. that you linked, but I will ask Sir Danie to explain it to me in a video.

tic.🤣

On 2023/06/28 at 4:50 PM, BritishRacingGreen said:

that on face value is a dead giveaway that the machine under test has no internal bonding. Which is true for those axperts before generation 3, ie the olders ones. 

A simple test will reveal this omission. If you disconnect all incoming and outgoing AC  connections on the machine, then test for continuity with your multimeter between IN neutral and OUT neutral. If none, test between OUT neutral and case earth. If none, there is no internal bonding. In this case you need to follow the nice procedure compiled by @Andrewj (CORRECTION @Eurard) which is available in this thread. It involves an external 10A rated bonding relay, operated by incoming mains. 

In my country, earthing or grounding from the customer side is generally not practiced. There's an ongoing debate among solar system installers regarding the use of the grid's neutral for the inverter's neutral. Around 80% believe this is incorrect, arguing that separate neutral lines should be installed in the house. Personally, I don’t see a problem with connecting the grid and inverter neutrals.

 

For context, we experience extreme power rationing, with only 1 hour of public electricity followed by 5 hours of blackout. Despite this, we don’t go fully off-grid and try to make the most of that 1 hour of grid power. What’s your advice on this?

5 hours ago, esmail-kassir said:

In my country, earthing or grounding from the customer side is generally not practiced. There's an ongoing debate among solar system installers regarding the use of the grid's neutral for the inverter's neutral. Around 80% believe this is incorrect, arguing that separate neutral lines should be installed in the house. Personally, I don’t see a problem with connecting the grid and inverter neutrals.

 

For context, we experience extreme power rationing, with only 1 hour of public electricity followed by 5 hours of blackout. Despite this, we don’t go fully off-grid and try to make the most of that 1 hour of grid power. What’s your advice on this?

Thank you for your interesting post. However I must respecfully disagree with both parties. There are 2 scenarios :

 

1. When grid is available to the inverter and the inverter is in line mode then the load neutral depends on the grid  neutral. The load neutral must not be bonded to earth as this creates an earth loop to the upstream bond and you have unwanted   neutral return paths through earth. 

2. When grid is not available at the inverter, no assumption can be made that the grid neutral is still bonded to earth. Case in point : the upstream double pole circuit breaker could have tripped and as a result the downstream neutral is now just a piece of floating cable. Therefore it is essential that the inverter disconnects the grid input via internal relay and then bonds the load neutral onto earth via a bonding relay contact. This then is a reconstructed neutral but isolated from the grid neatral ( islanding) . Extremely important for safe operation. 

39 minutes ago, BritishRacingGreen said:

Thank you for your interesting post. However I must respecfully disagree with both parties. There are 2 scenarios :

 

1. When grid is available to the inverter and the inverter is in line mode then the load neutral depends on the grid  neutral. The load neutral must not be bonded to earth as this creates an earth loop to the upstream bond and you have unwanted   neutral return paths through earth. 

2. When grid is not available at the inverter, no assumption can be made that the grid neutral is still bonded to earth. Case in point : the upstream double pole circuit breaker could have tripped and as a result the downstream neutral is now just a piece of floating cable. Therefore it is essential that the inverter disconnects the grid input via internal relay and then bonds the load neutral onto earth via a bonding relay contact. This then is a reconstructed neutral but isolated from the grid neatral ( islanding) . Extremely important for safe operation. 

 

@esmail-kassirI fully agree with the above statements. To reiterate the above in a slightly diffrent manner. 

 If you permanently connect the AC output to earth, when the inverter switches to bypass mode, it links the AC output neutral (N) to the AC input neutral (N), and thus to earth via the neutral link. As a result, some of the load current will flow through the AC output neutral to the permanent earth connection, then through the earth conductors, back to the neutral link, and finally to the transformer. This non-fault current flowing through the earth conductors is problematic because it can cause a voltage rise in the earthed metal parts of appliances. Moreover, earth conductors are not designed to handle continuous load currents, even though most of the current typically flows through the expected path via the inverter and back to the main switchboard or distribution board through the AC input wire.

In other words, there will always be continuity between AC input neutral and AC output neutral, as both are connected to earth. When the inverter is operating in battery mode, current will follow the long path described. When the inverter is in bypass mode, the relay switching will interrupt this direct connection between AC output neutral and earth. Instead, the neutrals of the inverter will be connected through the other pole of the neutral "safety" relay.

 

2 hours ago, TaliaB said:

@esmail-kassirI fully agree with the above statements. To reiterate the above in a slightly diffrent manner. 

 If you permanently connect the AC output to earth, when the inverter switches to bypass mode, it links the AC output neutral (N) to the AC input neutral (N), and thus to earth via the neutral link. As a result, some of the load current will flow through the AC output neutral to the permanent earth connection, then through the earth conductors, back to the neutral link, and finally to the transformer. This non-fault current flowing through the earth conductors is problematic because it can cause a voltage rise in the earthed metal parts of appliances. Moreover, earth conductors are not designed to handle continuous load currents, even though most of the current typically flows through the expected path via the inverter and back to the main switchboard or distribution board through the AC input wire.

In other words, there will always be continuity between AC input neutral and AC output neutral, as both are connected to earth. When the inverter is operating in battery mode, current will follow the long path described. When the inverter is in bypass mode, the relay switching will interrupt this direct connection between AC output neutral and earth. Instead, the neutrals of the inverter will be connected through the other pole of the neutral "safety" relay.

 

Interesting info but I believe that I didn’t make my idea Clear

I’m not asking about grounding. I’m not just asking about if it’s OK to connect output a neutral of theInverter with the grid neutral 

3 minutes ago, esmail-kassir said:

Interesting info but I believe that I didn’t make my idea Clear

I’m not asking about grounding. I’m not just asking about if it’s OK to connect output a neutral of theInverter with the grid neutral 

I think @BritishRacingGreen answered you correctly based on the assumed question, @TaliaB did the same with even more technical explanations, based on certain assumptions.

 

"Is it OK?" is a broad subject, and each person will answer based on their assumption of what you are asking, where you are asking from, which inverter you are asking about, and for whom.

Are you asking if it is "legally" OK (or even mandatory) to bond the incoming and outgoing inverter neutrals (according to the electrical laws/standards in your country or utility - of which I don't think you mentioned)?

Are you asking if it is OK from an electrical safety perspective (to the end user, or the inverter service person, or the electrical utility supply operator person)?

Are you asking if it is OK for the inverter or other electrical appliances (will it damage them in any way, under normal and/or abnormal circumstances)?

I don't have the clean cut answers unfortunately, but it would be fair to say that each of the above may be answered with "depends" based on the specific scenario.

Perhaps if you are more specific, someone can give you a more specific answer.

 

For example, here is an extract from a Sunsynk user manual which shows the incoming and outgoing neutrals separate in one diagram but also coupled in another. These different wiring methods are based on different geographical region standards or the standards of a specific electrical utility or even the exact electrical design of how the wiring gets from your specific local transformer to the electrical box in your specific house (TN-S/TN-C/etc). Do not take this diagram as truth either, as I think they get it a bit incorrect in part because even they do not know the rules for every region/utility, and it was probably a mistake to include it, for it has sent many on the wrong path based on incorrect assumptions of locality and system design.

 

Hope this info helps, sorry to hear of your electrical supply situation. It is familiar situation to some of us also (South Africa), though not quite as bad as you have described (yet?)

 

23 hours ago, WillHza said:

Are you asking if it is OK for the inverter or other electrical appliances (will it damage them in any way, under normal and/or abnormal circumstances)?

Actually that what I am concerned about.

I am in Syria, actually no regulations here . The only illegal thing here is to do electrical work before the electricity meter

 

Eve though I am concerned about safety but I am discussing this here as I have no clue how things handled from public transformer side , also there is no earth or grounding in my building and no regulation to follow. I only have control on my home connection ( inside my house) 

On 2024/09/13 at 10:50 PM, esmail-kassir said:

Actually that what I am concerned about.

I am in Syria, actually no regulations here . The only illegal thing here is to do electrical work before the electricity meter

 

Eve though I am concerned about safety but I am discussing this here as I have no clue how things handled from public transformer side , also there is no earth or grounding in my building and no regulation to follow. I only have control on my home connection ( inside my house) 

Please do not use what I say below as the right answer, this is just my understanding based on my experiences and research. I also do not know how your grid power is transformed and ultimately delivered to your house, other than what is available on the internet (380V 3-phase or 220VAC single phase 50Hz, euro style three pin L-N-PE outlet sockets). So I assume a lot of things based on South African grid standards, which are very similar to many western European grid designs (IEC derived standards).

To answer basically, if you have no legislation or guidance from your utility (unlikely, but maybe just ignored due to the nature of the situation) you can actually build a system WITH the bonding of the input and output neutrals or WITHOUT bonding the input and output neutrals. BUT each scenario has it's own set of rules that must be followed in order to make a system that is safe to the user. 

Safe to the user means you have a good Earth Fault return path (PE) to the generator/transformer/inverter supplying the power and a rapid disconnect in the event of someone or something touching the live wires in the system. In this event an overload switch (Circuit Breaker/CB) and more importantly an earth leakage detection switch with or without an overload (Earth leakage/RCD or RCBO) should rapidly disconnect the load should 30mA or more current imbalance be detected on the circuit (considered the non-lethal limit). In both cases this can only work if there is a connection at some location after the step-down transformer of the Neutral wire (N) and the Earth Fault wire (PE). As a rule there should only be one PE-N bond in the circuit, otherwise currents can be allowed to flow continuously on the PE wire and other conductive metal objects such as casings/waterpipes/gas pipes/etc, which they are not designed for.

Scenario 1 : When you are making an installation with the In/Out Neutral permanent bond you are assuming that the electrical utility supplier has made this PE-N bond connection and maintains this connection somewhere upstream/before the meter . It may or may not be true in Australia that this is the case.  The utility will can manage the PE-N bond for you whether in on-grid or off-grid mode. You would not make your own PE-N bond in an off-grid scenario in this case. This is not allowed in South Africa.

Scenario 2 : When you are making an installation and are not doing a permanent In/Out Neutral bond at the inverter, you are taking responsibility for managing your own PE-N bond when you are running in off-grid mode. This is a requirement in the standards in South Africa if you are installing the inverter some distance from the utilities PE-N bond (a home installation for example) and it may or may not be  a requirement in Germany and the UK also. In this case you will need to rely on a relay/contactor controlled by the inverter that bonds the PE and N when in off-grid mode and disconnects it, to make use of the utilities PE-N bond, when in on-grid mode. Some inverters contain this bonding relay inside the unit and some only provide a control signal output so that an external bonding relay/contactor can be installed external to the device. These bonding circuits are usually activated or deactivated in the system software or with external jumpers.

The Scenario 1 is probably only a good idea if you have a well functioning and maintained grid network and also an honest population or well protected grid facilities. In places with opportunistic criminality, the PE-N bond is commonly stolen for it's copper value from the utility side, leaving the user vulnerable to electrocution should a fault occur. Also if your incoming isolator switch isolates the Live AND Neutral wires (a requirement in South Africa), then by opening this switch you break the Neutral to the utility, and therefore also the utilities PE-N bond from your backup power circuit.

Also worth mentioning, if you have a cheap/small UPS style battery backup inverter, you may find that the neutrals are already bonded, and they also provide no facility for signalling when the inverter is in online or offline mode. These inverters should never be permanently installed and are best only ever plugged into a wall socket to provide a temporary power bridge during momentary power outages to small appliances in close proximity. 

To others reading this, if I have made an error above, I'm happy to be corrected.

 

Examples:
See this video of setting up the Huawei Grid tied inverters "off-grid backup box". At 5mins 40sec they talk about setting up the system for the bonded neutrals and for unbonded neutrals scenarios "according to the local power grid standard" using bridging jumpers.

On a Sunsynk/Deye it is called "Signal Island Mode" in the settings, and controls a low current signal output (5kW/8kW/16kW). Screenshot provided previously of the wiring connections.

Is this a viable installation diagram?

Grid power is going into meter to the left, there it PEN/ is turned to PE/N and PE is connected to earth ground rod

3 wires are now going to a small electrical box with an MCB/RCD to protect anything connected to grid power.. 

3 wires are going to the inverter (and also to some grid powered devices in the same installation - inverter is only supplying hald the loads essentially).

Assuming the inverter has the internal PE/N contact relay 3 wires go to an MCB/RCD to the output of the inverter and from them to the loads. 

AC connections to the inverter would look like this withinput PE cable connected to the terminals but, output PE cable connected to the inverter chasis .....

Since the inverter does not have a dry contact, is it logical to assume it has the internal relay for PE/N bonding in battery mode? If that proves not to be the case how can one add a relay to bond PE/N at the output of the inverter in battery mode?? 

I intent to use this in SBU mode meaning it will either run on solar/battery OR grid when battery is empty. 

Is there a problem having two RCD in series when in grid power mode?

The inverter will be in a small closet/storage room and I plan having a grid powered outlet as well as an inverter powered outlet for local use (mainly lights or electrical tools) so the RCD on grid side makes sense right? plus, it grid will still be supplying power to half the appliances in the building for a good few months at least until the system is completed with additional batteries and solar panels...