Solar Panel Configuration and Solar Panel Combiner box

[Cabo35]

Hello Everyone,

and thanks for your help in advance. Hope I'm not too redundant on the beginners forum with my questions.

I'm setting up a 12KW Growatt Split Phase Off-Grid Inverter SPF 12000T DVM MPV - Link for Specs is Below:

Growatt 12kW Split Phase Off-Grid Inverter | SPF 12000T DVM MPV

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I would like to install fifteen 460Watt 50V Panels in a series-parallel configuration if this is the most optimal configuration. Currently my home uses between (34kWh-44kWh) per day based on my electric bill. The system will have a backup battery bank of six 48V EG4 LifePower4 Lithium batteries at (100 AH and 5.12 kWh each). I average about 8.2 Peak hours of sunlight in my area each day.

Currently in my home I have a main breaker panel that supports the electrical loads for lights, appliances,TV's, computers, refridgerator, two mini split 18000 BTU A/C units, etc.. inside the main home. I believe the main breaker box is an 100 amp box, and I also have a sub-panel I believe that's 40 amps to power other loads in the home, such as a home water pump, washer/dryer, water filter, and water softener system. I would like to operate totally off-grid if possible. I also plan to have other electrical loads, lights, 120V outlets, and a vent fan in my new Solar shed.

I addition I want to add a breaker between the 30KW battery bank and the Growatt inverter. Hope this is not overkill since each 48V EG4 battery has a separate breaker.


Questions:
1). What would be the optimal PV array configuration for my Solar Panels with my Growatt inverter, based on the spec sheet?
2). What type of PV Combiner box do you recommend for my Solar Panel setup and why?
3) Does the PV Combiner box come with fuses and breakers for each array string or are the fuses separate for each?
4). Does the PV Combiner Box ground the PV arrays?
5). What type of breaker box do I need to connect to the Growatt inverter, and how do I determine the amperage size.
Again my home is Split phase 120V/240 for North America.
6). Is there anything that I need to be aware of with the new breaker panel that will be installed in the Solar shed since I already have a main panel and sub-panel in the home?
7) Since the home is obviously already grounded, do I need another ground for the new breaker box that will be installed next to the Growatt inverter?
8) Should the battery bank be grounded? How?


Again, thanks for your help and responses in advance,

Respectfully,
Cabo35

 

[MichaelK]

I'll try to go through these one by one....

1). What would be the optimal PV array configuration for my Solar Panels with my Growatt inverter, based on the spec sheet?
Your inverter only has one MPPT PV input, so that means all the strings MUST be the same voltage, which can be between 60 and 245V. The only viable combination I can see is 3S5P. (460W X 15panels)/50Vcharging = 138A. The Amp limit of your unit is 120A. Assuming your panels are derated to 85%, you are likely to see as much as ~117A going into the batteries.

2). What type of PV Combiner box do you recommend for my Solar Panel setup and why?
I like Midnight. I bought Midnight's charge controller, so I also bought their combiner. I have the six breaker unit. You would need 5 breakers.

3) Does the PV Combiner box come with fuses and breakers for each array string or are the fuses separate for each?
Combiners almost always use breakers, not fuses.

4). Does the PV Combiner Box ground the PV arrays?
No, the combiner is usually grounded to the main system ground, usually your inverter or the main electrical panel. The solar panels are grounded independently.

5). What type of breaker box do I need to connect to the Growatt inverter, and how do I determine the amperage size.
Again my home is Split phase 120V/240 for North America.
I have a Schneider split-phase inverter for my system, so I bought a Schneider specific breaker box for it. I don't know if Growatt has a similar unit. Most likely though you can buy something and adapt it. BTW, the breaker panel for the inverter itself is NOT the same thing as the main electrical panel. My Schneider panel outputs to the main electrical panel
6). Is there anything that I need to be aware of with the new breaker panel that will be installed in the Solar shed since I already have a main panel and sub-panel in the home?
Power from the inverter and power from the grid MUST NEVER meet. You MUST have a transfer switch or either/or breaker-toggle that always keeps them separate. This is a critical safety issue. Lineman can be killed working on a electrical line powered via your inverter.

7) Since the home is obviously already grounded, do I need another ground for the new breaker box that will be installed next to the Growatt inverter? There should be one and only one connection between all the above ground earthing components and your primary earthing electrode. All the ground wires to each solar component should meet at the same grounding bussbar (except the panels themselves).

8) Should the battery bank be grounded? How? No. The batteries of a home system are typically not grounded.

 

[Cabo35]

I'll try to go through these one by one....

1). What would be the optimal PV array configuration for my Solar Panels with my Growatt inverter, based on the spec sheet?
Your inverter only has on MPPT PV input, so that means all the strings MUST be the same voltage, which can be between 60 and 245V. The only viable combination I can see is 3S5P. (460W X 15panels)/50Vcharging = 138A. The Amp limit of your unit is 120A. Assuming your panels are derated to 85%, you are likely to see as much as ~117A going into the batteries.

2). What type of PV Combiner box do you recommend for my Solar Panel setup and why?
I like Midnight. I bought Midnight's charge controller, so I also bought their combiner. I have the six breaker unit. You would need 5 breakers.

3) Does the PV Combiner box come with fuses and breakers for each array string or are the fuses separate for each?
Combiners almost always use breakers, not fuses.

4). Does the PV Combiner Box ground the PV arrays?
No, the combiner is usually grounded to the main system ground, usually your inverter or the main electrical panel. The solar panels are grounded independently.

5). What type of breaker box do I need to connect to the Growatt inverter, and how do I determine the amperage size.
Again my home is Split phase 120V/240 for North America.
I have a Schneider split-phase inverter for my system, so I bought a Schneider specific breaker box for it. I don't know if Growatt has a similar unit. Most likely though you can buy something and adapt it. BTW, the breaker panel for the inverter itself is NOT the same thing as the main electrical panel. My Schneider panel outputs to the main electrical panel
6). Is there anything that I need to be aware of with the new breaker panel that will be installed in the Solar shed since I already have a main panel and sub-panel in the home?
Power from the inverter and power from the grid MUST NEVER meet. You MUST have a transfer switch or either/or breaker-toggle that always keeps them separate. This is a critical safety issue. Lineman can be killed working on a electrical line powered via your inverter.

7) Since the home is obviously already grounded, do I need another ground for the new breaker box that will be installed next to the Growatt inverter? There should be one and only one connection between all the above ground earthing components and your primary earthing electrode. All the ground wires to each solar component should meet at the same grounding bussbar (except the panels themselves).

8) Should the battery bank be grounded? How? No. The batteries of a home system are typically not grounded.

I know this reply is extremely late, but I want to thank you for taking the time to reply..

 

[SniperX]

On the question of whether combiner boxes come with fuses and breakers for each array string- Watt247 combiner boxes have individual fuses for each string and then breakers. Check them out.

 

[zack6736]

I have a question. In response #5 from MichaelK he talks about a breaker box after the inverter and that his line goes straight to his main panel. What are the main reasons for having a breaker box right after the inverter since it’s going to the houses main breaker panel, and will an average 100 or 200 amp breaker panel work right after the inverter or must they be a special box? Thank you and I don’t mean to hijack the thread?

 

[MichaelK]

What Midnight calls it is a "power center". It has both AC and DC breakers to control both the power coming into and the power going out of the inverter. It's basically just a metal box with all the slots for properly holding all the various breakers involved. Most likely it is a code compliance device to make sure the unit can be totally separated from the grid.

 

[zack6736]

What Midnight calls it is a "power center". It has both AC and DC breakers to control both the power coming into and the power going out of the inverter. It's basically just a metal box with all the slots for properly holding all the various breakers involved. Most likely it is a code compliance device to make sure the unit can be totally separated from the grid.

Thank you for your response. For the AC going out from the two LV6548s will just use a small two leg breaker box then before the lines head to the main panel in the house. My PV lines coming in will be connected to a DC disconnect switch before the inverters so I should be good. No codes here where I live thankfully. County seat has a population of about 2000 and my little town less than 180.

 

[MrM1]

FWIW, I'm Using the Watts247 4 in 2 Out combiners (x2) with my 11.8kw array. Because the Growatt 12k 250v can only take 7000 watts of PV (3500w on pv1 and 3500w on pv2) I also purchased a second Growatt 120a MPPT charger. That is why I am using 2 combiners 4 in 2 out. I have the array wired 4s and 8 strings (4 stings into each combiner). This keeps me well under the 250v VOC of the MPPTs and under the 3500w per pv input limit. Its a bit overkill, but this will keep all components from running at max all the time, thus keeping things cooler.

I have not installed the Watts247 combiners yet, but they appear very solid and probably the best value for the money out there as everything is included.

 

[SniperX]

FWIW, I'm Using the Watts247 4 in 2 Out combiners (x2) with my 11.8kw array. Because the Growatt 12k 250v can only take 7000 watts of PV (3500w on pv1 and 3500w on pv2) I also purchased a second Growatt 120a MPPT charger. That is why I am using 2 combiners 4 in 2 out. I have the array wired 4s and 8 strings (4 stings into each combiner). This keeps me well under the 250v VOC of the MPPTs and under the 3500w per pv input limit. Its a bit overkill, but this will keep all components from running at max all the time, thus keeping things cooler.

I have not installed the Watts247 combiners yet, but they appear very solid and probably the best value for the money out there as everything is included.

Your post cannot be more timely! I have an 8-2 Watts247 combiner box (actually bought 2) with the same Growatt 12k 250V and I also purchased an additional Growatt 120A MPPT charger to try to do the same thing. When you get yours set up, can you come back here and post pics with descriptions? I cannot figure out if I am supposed to hook the second charge controller straight to the batteries or how to do that to the Growatt. I am still trying to get this all figured out. I would greatly appreciate it.

 

[MrM1]

I've got a build thread. But here's the basic idea. I drew up this battery diagram before I added in the second charge controller. But I think I will add another bus bar where I marked it in for the controller



And then this is my basic wiring diagram. Again before I had the second charge controller but the basic idea will be something like this



The first picture is a close up of the batteries and the battery wiring. The second picture is a more General overview of all of the wiring. I also do not have my two 4 in 2 out combiners drawn

Also in these drawings some of my fuses and Breakers are no longer the correct size because I have reconfigured things a little. But the wires are correct. Adding to charge controllers I am going to use smaller Breakers and number 8 wire instead of number six from the combiner to the inverter charger

 

[MrM1]

Your post cannot be more timely! I have an 8-2 Watts247 combiner box (actually bought 2) with the same Growatt 12k 250V and I also purchased an additional Growatt 120A MPPT charger to try to do the same thing.

I am not sure I am following you with an 8-2 combiner. The Growatt inverter has two PV inputs and the Growatt MPPT has 2 inputs.

That is why I bought 2 combiners. 4-2 each.

If you only use one of the inputs on the inverter or charge controller, you limit yourself to only half of the PV input

 

[MrM1]

Here's my build thread

Off Grid Farm ~ Mobile Power Cargo Trailer Build: Growatt 12kw Install

Installing The Big Growatt SPF 12000T 12kw Inverter into a Cargo Trailer for a 12k watt mobile power generator. All the panels will be installed on a pole/post barn and I will connect the Inverter's Solar Charge Controller MPPT to the panels via 8 awg SOOW cable and Anderson Connectors. First...

diysolarforum.com

 

[SniperX]

I am not sure I am following you with an 8-2 combiner. The Growatt inverter has two PV inputs and the Growatt MPPT has 2 inputs.

That is why I bought 2 combiners. 4-2 each.

If you only use one of the inputs on the inverter or charge controller, you limit yourself to only half of the PV input

I just bought some property in N Central Florida and figured if I was putting up a solar array, I could use the same PV ground system but split the arrays and use two separate Growatts to power a small house and then run the other PV array to the garage with the second Growatt for the power in the garage. I hope I can do that because I have a very limited understanding but trying to figure this out. This was what I wanted to achieve. I have 11.84 acres and also want to build a very large workshop that will also need solar power, so I was thinking of the expansion for future.

 

[MrM1]

You can power 2 separate sub panels or loads panels with 2 Growatt inverters ... BUT NOT TOETHER. Growatt inverters are NOT stackable, cannot be run in parallel. So if you have 2 inverters you would create 2 separate power systems that would not share anything.

 

[SniperX]

You can power 2 separate sub panels or loads panels with 2 Growatt inverters ... BUT NOT TOETHER. Growatt inverters are NOT stackable, cannot be run in parallel. So if you have 2 inverters you would create 2 separate power systems that would not share anything.

I know. The picture just shows the PV and how it would be wired to go to two separate mppts for the 8-2 combiner box. They would not be in parallel. I wanted one unit in the house and one in the garage to function independently. The dashed line that may look like they are together is just the grounding part.

 

[SniperX]

I know. The picture just shows the PV and how it would be wired to go to two separate mppts for the 8-2 combiner box. They would not be in parallel. I wanted one unit in the house and one in the garage to function independently.

I've got a build thread. But here's the basic idea. I drew up this battery diagram before I added in the second charge controller. But I think I will add another bus bar where I marked it in for the controller

View attachment 110795

And then this is my basic wiring diagram. Again before I had the second charge controller but the basic idea will be something like this

View attachment 110796

The first picture is a close up of the batteries and the battery wiring. The second picture is a more General overview of all of the wiring. I also do not have my two 4 in 2 out combiners drawn

Also in these drawings some of my fuses and Breakers are no longer the correct size because I have reconfigured things a little. But the wires are correct. Adding to charge controllers I am going to use smaller Breakers and number 8 wire instead of number six from the combiner to the inverter charger

Can you tell me which switch you bought and where? It is on the first picture and it is the round cut-off switch at the bottom of the wiring going to the inverter (says M10 4/0 x4 right above it) I am looking for a switch like this but do not know how to size, what I need to look for, etc.

 

[MrM1]

Download and review this design. This is how to build the switch and inverter precharger. The switch for 48v is the BEP

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

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