Newcomer

[Bigjayjay69]

Hello all, I am new to setting up a complete off grid system, however i have been an electrician all of my adult life and have a good basic understanding of how solar power works and the basics of inverters, battery racks, series and parallel and such. i am trying to put together a 16KW PV using (44) 365W panels utilizing (4) strings of (11) panels , (4) EG-4 6.5KW inverters, and (6) EG-4 LifePower4 48V 5.12KWh batteries. i intend to have (2) inverters in parallel for each line of split phase 240V /120V Off grid system. Part of my concern is in the max PV input for the inverters as it is rated for 8000W max and has 2 possible inputs, 4000W/ 18A each. But since there will be the split phase in the configuration am i correct in believing i will be able to connect 2 strings to one side or leg and the other 2 strings to the other leg which will basically be connected in parallel with the second inverter on each side?

Thank you very much in advance for any advice anyone cane share...

Jason

 

[Samsonite801]

It's better to think of the all-in-one inverter as having a separate charge controller and separate inverter inside them. The charge controllers are just PV solar battery chargers, charging on a common battery bank. The inverters are doing their own thing so there is no relationship (on the split-phase output) as to which PV inputs you are using to charge the battery bank with...

 

[Bigjayjay69]

Ok, that makes sense, so then would it be best to run (2) strings to one inverter on line 1 side and other 2 strings to one inverter on line 2 side, or should one string go to each of the 4 inverters?

 

[Samsonite801]

Ok, that makes sense, so then would it be best to run (2) strings to one inverter on line 1 side and other 2 strings to one inverter on line 2 side, or should one string go to each of the 4 inverters?

That all depends on how many solar panels you can wire into series without overvolting any given solar input. Solar panels and charge controllers go together like a horse and carriage to a great extent. Even if I didn't utilize all 4 inputs initially, I would consider provisioning 4 cable runs when doing the initial cable pull, just for future use, to make it easier to expand more panels later.

Have a look at this site and use the calculator:

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

The goal is to do as many panels in series as you can, so the volts is higher and can allow for smaller gauge cable (less amps), without going over on max PV volts of the charge controller. The charge controllers are typically bit more forgiving on the max 18a input in many cases (overpaneling on amps), because the charger can clip the solar amps by not drawing too many amps on the input (usually still they have some kind of physical wiring in the hard Isc maximum rating, though not usually published), but you definitely cannot go over the max PV input voltage spec (also taking into account for coldest temperature coefficient of Voc, which the above article gets into the details on that).

 

[Bigjayjay69]

im good with respect to amount of panels on a string. the panels are 33.5V and just under 11Amps, so the 11 panels are 369V totaling just over 4000W. if i paralleled strings i would be at about 22A and with the inverter clipping at 18A i would be wasting 4 Amps so i know not to be paralleling the strings. im just wanting to know if since i will have 4 inverters and 4 strings of panels should i put one string on each inverter or is it better to put 2 strings on an inverter since it has the two separate 4000W PV ports, and connect that inverter in parallel with a second inverter to feed one leg,or Line1 and then do the same for Line 2 with the other two strings and 2two inverters?

 

[Samsonite801]

Single strings would keep current lower against each MPPT controller circuit, and would help them run cooler (and could last longer?)... You can use all 8 inputs on any of the 4 inverters as you like. The inverter circuit portion and the charge controller portion are not tied together, it doesn't matter which of the 4 PV inputs you use or don't use...

 

[Bigjayjay69]

Ok thanks so basically i can connect them like shown in this drawing, either configuration is fine, the one on the bottom with a separate string to each would possibly have an advantage as far as them all running a little cooler is what you are saying?

 

[Samsonite801]

No.. You can't hook a solar string (circuit) to 2 MPPT inputs (as per top diagram)... One MPPT controller must have exclusive control of a PV circuit.

As far as what I was referring to before, it was 1p vs 2p (11a vs 22a), as being what would or could make it run cooler or last longer (which it could be argued that it may not even matter or provide any benefit)...

 

[Bigjayjay69]

ok good this is the kind of confirmation I have been looking for, if I only had 2 inverters I would have 2 strings on each inveter and when it is talked about stacking or paralleling a couple inverters, you can parallel the charging of the battery bank connections and of the ac output connections, but you don't parallel the PV array connection with another inverter.
Thank you very much for you input it has been very helpful. Perhaps one day I will be able to help you the same , if you ever need input regarding typical AC Voltage concerns hit me up , been an electrician for over 30 years

 

[Samsonite801]

ok good this is the kind of confirmation I have been looking for, if I only had 2 inverters I would have 2 strings on each inveter and when it is talked about stacking or paralleling a couple inverters, you can parallel the charging of the battery bank connections and of the ac output connections, but you don't parallel the PV array connection with another inverter.
Thank you very much for you input it has been very helpful. Perhaps one day I will be able to help you the same , if you ever need input regarding typical AC Voltage concerns hit me up , been an electrician for over 30 years

Yeah, the only charge controller paralleling that 'could' potentially exist (across the all-in-ones), is if whether the vendor might use paralleling-stacking communication to synchronize the battery charging stages across inverters. As far as I know, none of the consumer all-in-one inverter/ charge controllers support syncing charge stages across the multiple charge controllers.

I do run a pair of Victron charge controllers in conjunction with a BMV smart battery monitor, where I've enabled Victron's sync charging mode, where you create a network group (in my case via bluetooth connection), by adding all the chargers into the group (in the VictronConnect app), along with the BMV battery monitor (single point to read battery voltage, current, and temperature), and it delegates one of the chargers to be a master, and other ones are slaves, then all the chargers will stay on the same battery charge cycle together. This helps to optimize the max watts charging potential, so one charger doesn't go into float too soon (as they are all reading slightly different voltages), while others might still be in absorption stage or something.

It's not a huge requirement (can also manually tweak and calibrate the chargers' charge stage voltages (in small increments) to get the stages matched pretty close) but I would expect to see more manufacturers implementing this type of functionality into the parallel stackable all-in-ones at some point in the future, but for now, I don't believe any of them have this now. I think only Victron has done this (as far as consumer-grade solar equipment), but not totally sure...

Any function like this though, would be completely independent of what the inverter portion of the all-in-one is doing in regards to the AC output parallel operation.

 

[Bigjayjay69]

so are you saying I must connect one EG-4 battery to one one EG-4 Inverter in order to have everything else connected the way I have described?

 

[Samsonite801]

so are you saying I must connect one EG-4 battery to one one EG-4 Inverter in order to have everything else connected the way I have described?

No, not at all, all of the stacked inverters connect to, and share the same battery bank. It is fine for multiple battery chargers to charge on one bank. Sorry if I caused some confusion there.

 

[Bigjayjay69]

so it is best to have all 4 inverters connected to the 6 batteries in parallel then? is there any advantage to having 3 batteries connect to 2 inveterate for line 1 and the other 3 batteries connected to the other 2 inverters for line 2 since it. will be a split phase system?

 

[Samsonite801]

so it is best to have all 4 inverters connected to the 6 batteries in parallel then? is there any advantage to having 3 batteries connect to 2 inveterate for line 1 and the other 3 batteries connected to the other 2 inverters for line 2 since it. will be a split phase system?

The fact that it is split-phase on the AC outputs plays no role in the battery topology configuration. But to also note, it's important to consider how the manufacturer says it should be cable in..

One thing I did when I bought my four MPP Solar LV6548's (even before I bought them), I read the entire manual, cover to cover, just so I could know about any important details...

https://signaturesolar.com/content/documents/EG4/6500ex/EG4_6.5_manual_revision2.pdf

See PDF Page 53 (Page 48 in document), see the WARNING!...

Also, reading the entire manual will fill in lots of other blanks and you will be so happy you did!




EDIT:
Also something to think about. Even if you did have multiple banks, what if one battery got too low and shut off that inverter, then you'd lose one leg, and all the 240v, and the cluster would be in fault anyway. Not to mention, with all the batteries paralleled, you get much better surging capacity to handle big motor startups and whatnot. In addition, all PV chargers can all read from a common voltage, and maximize effective charging (able to combine all wattage and charge the entire pack without being confined to a smaller battery). Their really wouldn't be any advantage to splitting a bank up across multiple inverters. Just some food for thought.