Replacing 10-yrs old inverter with a new one: help needed with grounding and more

[fablau]

Hello everyone, I am a newbie here.

Although I am a software engineer and have a strong knowledge of electrical systems and electronics, I am NOT an expert in solar installations, hence my questions here and my need for help.

I'd need to replace an old Aurora Power One 3600w inverter for my 3kW home PV grid-tied system, which has burned out after over 10 years of service, and I find myself unable to easily replace it with any of the new inverters available nowadays on the market. My main problem is that most of the new inverters seem to not clearly explain how to ground both the grid and the PV side and have different characteristics and requirements from the old ones. I'll try to explain exactly what I am talking about here with pictures and data (below).

Here is a picture of how my system was previously hooked to the old inverter:



As you can see, both the output to the grid on the right and the PV input on the left are grounded (green cable).

Now, I am thinking of replacing that old inverter with a new one by Fimer, with similar characteristics:

Fimer UNO-DM-3.8-TL-PLUS-US-SB-RA-Q - Inverter Supply

Shop for Fimer UNO-DM-3.8-TL-PLUS-US-SB-RA-Q at Inverter Supply for best prices online. Fimer UNO-DM-3.8-TL-PLUS-US-SB-RA-Q, Fimer, UNO-DM-3.8-TL-PLUS-US-SB-RA-Q, Single-phase string inverter 3800Wac 2 MPPT, Fimer Inverters

www.invertersupply.com

You can find the installation manual at the link below:

https://www.fimer.com/sites/default/files/FIMER-UNO-DM-3.3_3.8_4.6_5.0-TL-PLUS-US-Q-Product%20manual%20EN-RevA%28M000050AG%29.pdf

And if you look through the manual, there is no picture showing how to connect the ground to the inverter. Furthermore, if you look at page 44 under the "Photovoltaic panel ground fault" section, you'll read the following:

This inverter must be used with photovoltaic modules connected with “floating” connections - that is, with positive and negative terminals that are not grounded. An advanced ground fault protection circuit continuously monitors the ground connection and disconnects the inverter when a ground fault is detected. The ground fault condition is indicated by a red LED on the front panel.


Does that mean that the ground MUST not be connected to the inverter? And if so, where do I need to connect it? And what about the ground from the grid side? It's very confusing to me, and I am stuck with this main problem to solve.

Another question I have is about choosing between "Independent channel configuration" and "Parallel channel configuration" (see page 62 of the same manual above). I don't know which one to choose because it looks like my old inverter didn't have that option! But from how it was hooked up, I guess it was in an "independent channel configuration" since I haven't noticed any "jumpers" in the old inverter and (as you can see from the picture above) the 4 wires coming from the PV system seem to be independent. Is there a proven way to understand that? What advice would you have for me on this?

And the last question for you guys is this: If you look at page 68 of the same manual, you'll see they talk about a "Rapid Shutdown" connection. It looks like that's something else I need to install, and I am wondering why I didn't have that in my previous inverter. Or was that already inside the inverter? Or is that already inside the fuse box I have for my home? Quite confusing to me...

Any thoughts and suggestions are very welcome!

Thanks in advance to anyone.

All the best,
Fab.

 

[Samsonite801]

This inverter must be used with photovoltaic modules connected with “floating” connections - that is, with positive and negative terminals that are not grounded. An advanced ground fault protection circuit continuously monitors the ground connection and disconnects the inverter when a ground fault is detected. The ground fault condition is indicated by a red LED on the front panel.

Does that mean that the ground MUST not be connected to the inverter? And if so, where do I need to connect it? And what about the ground from the grid side? It's very confusing to me, and I am stuck with this main problem to solve.

They are meaning that the negative (-) run going to the solar panels should NOT be grounded (PV negative is not to be Earthed). On a sidenote, the best way (in my opinion), to protect the PV circuit would be by installing surge arrestors inline on the PV runs. What that does is basically allow any surge over the voltage rating of the surge arrestor to have a path to ground, but normally it is floating.

As far as the inverter itself, it should be treated like an appliance and the chassis of it should be grounded to your main panel service ground.

Another question I have is about choosing between "Independent channel configuration" and "Parallel channel configuration" (see page 62 of the same manual above). I don't know which one to choose because it looks like my old inverter didn't have that option! But from how it was hooked up, I guess it was in an "independent channel configuration" since I haven't noticed any "jumpers" in the old inverter and (as you can see from the picture above) the 4 wires coming from the PV system seem to be independent. Is there a proven way to understand that? What advice would you have for me on this?

Do you simply have one single PV run coming from your solar panels/arrays (and one PV input on your old controller), or do you have 2 separate PV runs (arrays) coming in from outside (with more than one MPPT input on your old controller)?

This unit has 2 separate MPPT input circuits, but seems to offer the ability to bridge them together and make it as one single MPPT input circuit (assuming it would also double the amperage capability on the input when paralleled).

And the last question for you guys is this: If you look at page 68 of the same manual, you'll see they talk about a "Rapid Shutdown" connection. It looks like that's something else I need to install, and I am wondering why I didn't have that in my previous inverter. Or was that already inside the inverter? Or is that already inside the fuse box I have for my home? Quite confusing to me...

Modern systems, in many jurisdictions, are required to follow current National Electrical Code (NEC) code requirements for safety (related to NFPA - National Fire Prevention Association, fire / fireman safety).

Rapid shutdown is an electrical safety requirement that was originally introduced in the United States by the NEC. This requirement applies to solar PV systems and requires a way to de-energize, or reduce the voltage, of the solar modules on the roof by adding an on/off switch at an easily accessed location.

Fireman are trained that the first step when approaching a burning house is to first disable all power into/in the building to eliminate any electrocution / short-circuit dangers prior to entry (plus could also be a source and ongoing cause of the fire in the first place).

Since the firemen cannot easily disable the Sun during the daytime ( ), they need an conveniently-located, ground-level accessible, manual switch, which can remotely disconnect the power as close to the power source (the solar panels) as possible.

 

[fablau]

Thank you for your response! Please, see my further replies below, in context:

They are meaning that the negative (-) run going to the solar panels should NOT be grounded (PV negative is not to be Earthed). On a sidenote, the best way (in my opinion), to protect the PV circuit would be by installing surge arrestors inline on the PV runs. What that does is basically allow any surge over the voltage rating of the surge arrestor to have a path to ground, but normally it is floating.

As far as the inverter itself, it should be treated like an appliance and the chassis of it should be grounded to your main panel service ground.

Got it. Does that mean that I must somehow connect both the ground wire coming from the panels and the ground going to the grid to the chassis of the inverter? If so, I think there is a place for that (although they haven't mentioned it in the manual).

Do you simply have one single PV run coming from your solar panels/arrays (and one PV input on your old controller), or do you have 2 separate PV runs (arrays) coming in from outside (with more than one MPPT input on your old controller)?

This unit has 2 separate MPPT input circuits, but seems to offer the ability to bridge them together and make it as one single MPPT input circuit (assuming it would also double the amperage capability on the input when paralleled).

Yes, I think it has two different PV runs since what I get from the panels are 5 wires: 2 from one array and 2 from the other array, plus 1 ground wire. And they were connected separately inside the old inverter (see my posted picture above). Is this a correct assumption?

Modern systems, in many jurisdictions, are required to follow current National Electrical Code (NEC) code requirements for safety (related to NFPA - National Fire Prevention Association, fire / fireman safety).

Rapid shutdown is an electrical safety requirement that was originally introduced in the United States by the NEC. This requirement applies to solar PV systems and requires a way to de-energize, or reduce the voltage, of the solar modules on the roof by adding an on/off switch at an easily accessed location.

Fireman are trained that the first step when approaching a burning house is to first disable all power into/in the building to eliminate any electrocution / short-circuit dangers prior to entry (plus could also be a source and ongoing cause of the fire in the first place).

Since the firemen cannot easily disable the Sun during the daytime ( ), they need an conveniently-located, ground-level accessible, manual switch, which can remotely disconnect the power as close to the power source (the solar panels) as possible.

I already have two huge mechanical disconnects. One between the inverter and the grid, and one between the inverter and the solar panels. Is that sufficient then?

Thank you again.

 

[Samsonite801]

Got it. Does that mean that I must somehow connect both the ground wire coming from the panels and the ground going to the grid to the chassis of the inverter? If so, I think there is a place for that (although they haven't mentioned it in the manual).

Yeah, so the ground wire coming from panels (not PV negatives of course, but just to clarify), the ground coming from grid, and the inverter chassis should be grounded. The grid ground is actually coming from your main panel ground bus bar, and connected to the ground rod outside.

Yes, I think it has two different PV runs since what I get from the panels are 5 wires: 2 from one array and 2 from the other array, plus 1 ground wire. And they were connected separately inside the old inverter (see my posted picture above). Is this a correct assumption?

Get out a volt meter, and check/identify the leads. You should see circuit Voc (volts open-circuit) voltage for each array and be able to confirm which lead is positive and which is negative by confirming the voltage in the display of the voltmeter doesn't have a - (example: -0.00v) before the value (indicating a negative voltage, or reversed leads measurement).

You also need to check the specs on your panels, confirm the wiring configuration of them (series / parallel config), make sure the Voc max PV voltage doesn't exceed the max PV input voltage of your new PV controller (also factoring in the temperature coefficient compensated Voc value to include you coldest outdoor ambient temperature the panels will ever see).

Solar panel maximum voltage calculator - How to work out the max voltage

To get the maximum solar panel voltage you should expect from your solar panel, use our solar panel maximum voltage calculator.

gold-coast-solar-power-solutions.com.au

I already have two huge mechanical disconnects. One between the inverter and the grid, and one between the inverter and the solar panels. Is that sufficient then?

Thank you again.

You should check the NEC regs.

Here's an example:

How to comply with solar rapid shutdown requirements

See also: How to meet NEC 2017 rapid shutdown requirements NEC 2014 PV rapid shutdown requirements were added to NEC 2014 (690.12) to improve electrical

www.solarpowerworldonline.com

Now, we're coming soon into the new 2023 NEC... They periodically amend things in the codes over the years.


Here is some more info too (article below dated May 1, 2022):

Fire and Personnel Safety Requirements for Photovoltaic Systems

iaeimagazine.org

 

[fablau]

Wow, thank you so much! I'll review all that. Appreciated!