6 EG4 WallMount Batteries + 3 EG4 6000XP Inverters

[mossymeadow]

Hey fellow DIYers & solar enthusiasts!

I am installing an off-grid solar system for a 1400 sqft home I am currently building. The system will be installed in a metal barn, adjacent to the future home, where my wife and I currently live.

We have:
- 36 x Hyperion 400W Bifacial Solar Panel (14.4kW total)
- 3 x EG4 6000XP Off-Grid Inverter (18kW total)
- 6 x EG4-WallMount Indoor Battery (85.8 14.3kWh total)

System Details

Our panels are mounted in 6 strings of 6. The panels are 250 to 300 feet away from the barn. We will use 8 AWG copper wire to achieve a 2-3% voltage drop (depending on voltage).

Each of the 3 inverters have two MPPTS and will thus receive two strings. The string voltage should vary from 247.44V to 160.61V depending on temperature. The start up and max voltages on the inverters are 100V and 480V respectively. The PV input will be protected by a 32 AMP breaker & a 600V lightning arrestor.

The EG4 system does not natively support 6 parallel batteries with only 3 inverters, so we are paralleling them ourselves with multiple busbars. We have chosen to use multiple busbars in order to reduce wire length (the 6 batteries span 14 feet of wall space), to reduce clutter, and to be able to use the out-of-the-box battery connectors.

We propose to accomplish this by having three batteries connect to one "sub" busbar, the other three connect to a second "sub" busbar, and then those two "sub" busbars connect to the "main" busbar. The three inverters will also connect to the "main" busbar. This design keeps all batteries in parallel. Of course, the lengths of cables are all the same size (at any given level).

The manual recommends that the busbar and wiring support 200A for each battery (so, 1200A total), but, a 1200A wire is... unrealistic (right?).

The inverters can each discharge 140A and charge 125A for a total of 420A discharge and 375A charge, respectively. However, the total discharge will be limited by a 200A main panel. Each inverter's AC output will be back-fed to a 40A breaker using 8 AWG wire.

Thus, we are inclined to ignore the 1200A recommendation. The bus bars are all rated for 600A. We are using 2/0 AWG wire from the batteries to their "sub" busbars, 4/0 AWG wire to connect the "sub" busbars to the "main" ones, and 2/0 AWG wire to connect the inverters to the "main" busbars.

Question

My main concern with this wiring would be a potential failure mode where all three of the batteries on one of the sub-panels disconnect, the sun is blazing, and all 375A of charge is pushed from the inverters to the "main" busbar, to the only remaining active "sub" busbar, to the other three batteries. While the 4/0 cable from the "main" busbar to the "sub" busbar would happily take 50% of the 375A inverter charge, it would likely not be too happy if all 100% of that load fell onto it.

Thus I am considering paralleling a second 4/0 cable between each of the sub and main busbars. Of course, the second 4/0 cables would be of the same length, so the two cables would share the load evenly. Thoughts?

I will be installing this with a long time (40+ year) builder who is well experienced in wiring up traditional electric systems. He has his own off grid solar system at home, but, he is also not a full time solar installer. Meanwhile, I only started learning about electricity 2 weeks ago. Thus, I would appreciate any suggestions, hints, or words of caution.

I didn't discuss ground and neutral, so please feel free to review those in my diagram.

Thank you!! We are super excited to get this up and running.

 

[FilterGuy]

At first glance your plan looks pretty solid. One thing you should consider is to use the battery paralleling kits to parallel sets of three batteries and then use busbars to tie the two sets together.



This would be entirely within the specs of the inverters and batteries

Alternatively I would be tempted to parallel all 6 batteries. To ensure there are no issues, you could put some Class T fuses in between sets of two


The other thing I would do is drop the combiner box and feed the inverters directly into the main panel... But that assumes there is room in the main panel for three 40A 240V breakers.

I know Will likes the combiner box arrangement, but I don't see the point.

In normal operation the fuses would see very little current, but if one battery shut down, it could affect the balance and the current would go up. However, the sustained current would never be above 300A through any of the fuses.

 

[FilterGuy]

The other thing I would do is drop the combiner box and feed the inverters directly into the main panel... But that assumes there is room in the main panel for three 40A 240V breakers.

I know Will likes the combiner box arrangement, but I don't see the point.

 

[Hedges]

Or, call the "Combiner Box" a "Critical Loads Panel".
Add a load-shed relay before the Main Panel.

I think it is best to have 2 levels of load shed.
Critical loads like communications are always on.
Important loads like refrigeration and lighting are on down to maybe 20% SoC.
Heavy loads like laundry and HVAC are on down to maybe 50% SoC.

Filter Consultant - does the 6000XP have a signal to load-shed based on SoC or anything like that?

 

[hwy17]

I would use 10awg home runs for each string. You really don't need 8 awg for one string, voltage drop is acceptable for PV. I would actually use 12awg but 10awg is consensus advice.

I would use the powerpro's amphenol paralleling to put them into packs of 2 or 3 and then each pack I would connect by a 225A class T to an 8 stud 600A bus bar.

Then, I would connect each inverter through a 150A class T and 2 awg or larger.

All the class T's here I would use a linkbus to connect the holder to the bus bar. I'm not sure if the holder and bus bar heights align for that, if they don't the shorter one will have to be shimmed up to level.

This bus bar idea is not consensus advice, just my own, and it's based on blue sea components which are not technically rated for 48-60v use but commonly used out of spec for it anyway.

 

[mossymeadow]

Thank you all so much! We are incorporating this into our design. We will combine the combo box & main into a single panel for now and then think about critical loads once we build our real home. We will be adding some class T fuses - thank you. And we will use the internal battery busbar for connecting them into groups.

I have two follow up questions if you please:

1. By using the internal battery busbar, won’t the main battery (the one directly connected to the external busbar) get more usage than the other batteries it connects with (since those would have higher resistance from the extra cable hop)?

2. I have a 13kW generator (10kW continuous). The manual for the inverter says that when using a generator it should connect to all the paralleled inverters and, for 3 inverters, should be at least 20kW. Do you understand why this constraint exists?

Thanks again! Leo

 

[hwy17]

By using the internal battery busbar, won’t the main battery (the one directly connected to the external busbar) get more usage than the other batteries it connects with (since those would have higher resistance from the extra cable hop)?

It will result in some uneven battery circuit paths but I doubt you will be charging or discharging fast enough for it cause a problem. I have some very uneven batteries and they are fine. If they ever do get uneven they even up again on the next full charge.

Also I have not tested my link bus bus bar to class T holder idea. It's possible it might not fit on the holder stud.

On the generator requirement, I don't know. Hopefully someone else will.

 

[FilterGuy]

1. By using the internal battery busbar, won’t the main battery (the one directly connected to the external busbar) get more usage than the other batteries it connects with (since those would have higher resistance from the extra cable hop)?

As said above, there will be a little bit of uneven wear, but I would not worry about it. THe cycle count on these is so high it won't make a difference. furthermore as one battery gets weaker over time, the other will start taking more of the load.

For the most part each inverter will draw power from the two batteries it is directly connected to. The current through the fuses will only be enough to keep the batteries balanced.

 

[FilterGuy]

. I have a 13kW generator (10kW continuous). The manual for the inverter says that when using a generator it should connect to all the paralleled inverters and, for 3 inverters, should be at least 20kW. Do you understand why this constraint exists?

The 6000XP has gen boost. Your generator should work just fine.

 

[hwy17]

At first glance your plan looks pretty solid. One thing you should consider is to use the battery paralleling kits to parallel sets of three batteries and then use busbars to tie the two sets together.
View attachment 214176


This would be entirely within the specs of the inverters and batteries

Alternatively I would be tempted to parallel all 6 batteries. To ensure there are no issues, you could put some Class T fuses in between sets of two

View attachment 214181
The other thing I would do is drop the combiner box and feed the inverters directly into the main panel... But that assumes there is room in the main panel for three 40A 240V breakers.

I know Will likes the combiner box arrangement, but I don't see the point.

In normal operation the fuses would see very little current, but if one battery shut down, it could affect the balance and the current would go up. However, the sustained current would never be above 300A through any of the fuses.

I didn't read your post closely enough the other night to realize you'd already described the idea I later arrived at in your first diagram.