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Combine separate arrays or not
#1
I have 2 separate sets of pv panels, one connected straight to each grid tie inverter..
Panels being used for both arrays are similar but still slightly different,, one of the arrays produces roughly 140w less than the other at full production (1575w) but pv panel specs from both arrays are only different by a couple tenths of an amp and a couple tenths of a volt..

I am going to install batteries that will be supplying the inverters to save excess solar production.

Option 1; Combine the arrays and use one charge controller and parallel the two battery packs, so all panels and batteries supply both inverters, then the lower producing set of panels (140w less) with lower the production of the higher producing set of panels once all panels are combined.

Option 2; Keep the arrays separate (as they are now) and use two charge controllers and two separate battery packs, so each inverter would have its own set of panels charge controller and single battery. The higher producing array (140w more) will not have its production lowered by the lower producing array..

Roughly speaking, which option would be more efficient and why?
Would it be more efficient to combine the arrays and not having everything separate due to the efficiency loses of using multiple (2 arrays, 2 batteries 2 charge controllers) devices-power sources, even tho I’d still be losing the extra production I could have had from the higher producing array being kept separate?

More possibly helpful info ; The batteries that would be paralleled in option 1 are the same batteries that would be used separately in option 2..
The charge controller used in option 1 would be the outback 60 or 80 amp and for option 2 I would use two 150/35 victron charge controllers..
Both arrays are really close to each other on the roof and facing south, one below the other, no shading issues..
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#2
What’s the reason for no one commenting.. is there more information needed?
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#3
(09-26-2019, 06:49 PM)Doin it Wrote: I have 2 separate sets of pv panels, one connected straight to each grid tie inverter..
Panels being used for both arrays are similar but still slightly different,, one of the arrays produces roughly 140w less than the other at full production (1575w) but pv panel specs from both arrays are only different by a couple tenths of an amp and a couple tenths of a volt..

I am going to install batteries that will be supplying the inverters to save excess solar production.

Option 1;  Combine the arrays and use one charge controller and parallel the two battery packs, so all panels and batteries supply both inverters, then the lower producing set of panels (140w less) with lower the production of the higher producing set of panels once all panels are combined.

Option 2;  Keep the arrays separate (as they are now) and use two charge controllers and two separate battery packs, so each inverter would have its own set of panels charge controller and single battery. The higher producing array (140w more) will not have its production lowered by the lower producing array..

Roughly speaking, which option would be more efficient and why?
Would it be more efficient to combine the arrays and not having everything separate due to the efficiency loses of using multiple (2 arrays, 2 batteries 2 charge controllers) devices-power sources, even tho I’d still be losing the extra production I could have had from the higher producing array being kept separate?

More possibly helpful info ; The batteries that would be paralleled in option 1 are the same batteries that would be used separately in option 2..
The charge controller used in option 1 would be the outback 60 or 80 amp and for option 2 I would use two 150/35 victron charge controllers..
Both arrays are really close to each other on the roof and facing south, one below the other, no shading issues..

>both arrays are only different by a couple tenths of an amp and a couple tenths of a volt..
You describe the 2 PV arrays as essentially the 'same' / 'compatible' so you could combine them into 1 charge controller - and there are several on the market that can handle 3000w range.  
The typical reason you do multiple charge controllers is that the PV arrays are quite different OR combined they produce too much power for a single controller - so you add a 2nd, 3rd, etc.  

All controllers with same battery voltage output can hook to a single battery bank of compatible voltage.   One or more inverters (of same voltage range) can run from the same comptible battery bank.    I don't view efficiency as a reason for separate battery/inverters.  You might have separate systems for redundancy or for experimental/metric tracking purposes or because wiring (to a common physical location) might not make sense or just because you want to.
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#4
The arrays are already separate due to me not having batteries atm and due to me having two mppt inverters. Yes the panels that each array consist of are compatible (but not the same) and can be combined but each of individual panels of one of the arrays have slightly less wattage output compared to each of the individual panels of the other array.. that slightly less wattage equals roughly 140w difference between the individual arrays.. if I combine the arrays (using one charge controller) the array that produces less watts will bring down the watt production of the other array by the 140w..
So if I combine arrays I’m getting roughly 140w less at max production.
Having 2 controllers charging the same battery bank might cause confusion (maybe just in my brain) somehow idk.. Ik it can be done but I’d like to avoid that if possible.. would it be more efficient having 2 controllers to one battery or 2 controllers to individual batteries? I think I’m going to have a hard enough time figuring out how to properly charge a lithium battery bank with just one charge controller charging one battery..
So options still are; option 1; combine array to one charge controller and to one battery bank (2packs in parallel) losing the 140w...
option 2; keep arrays separate to individual charge controllers to individual battery banks, having loses from each individual part..
What’s the pros and cons of each option?
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#5
(09-27-2019, 06:07 PM)Doin it Wrote: Having 2 controllers charging the same battery bank might cause confusion (maybe just in my brain) somehow idk.. Ik it can be done but I’d like to avoid that if possible.. would it be more efficient having 2 controllers to one battery or 2 controllers to individual batteries? I think I’m going to have a hard enough time figuring out how to properly charge a lithium battery bank with just one charge controller charging one battery..
A lithium battery has a top limit.  You set a charge controller Absorb/Float to the top voltage (or less as you desire) for the battery.  You describe that you will have 2 controllers - and assuming the battery(s) are the same nominal voltage - then the settings are the same for both controllers regardless of whether you have 1 battery or 2 batteries.   A single battery does not care if it get's charging current from 1 or 2 or 20 sources..  the battery only cares that it is not overcharged.    There is no power efficiency in having 2 batteries as apposed to 1.  


(09-27-2019, 06:07 PM)Doin it Wrote: So options still are;
option 1;  combine array to one charge controller and to one battery bank (2packs in parallel) losing the 140w... 
option 2;  keep arrays separate to individual charge controllers to individual battery banks, having loses from each individual part..
What’s the pros and cons of each option?
2 charge controllers to 1 (combined) battery is identical power (efficiency) wise to 2 charge controllers to 2 batteries - assuming the batteries have the same nominal voltage.    You don't loose 140w with 2 charge controllers to 1 battery, the 140w simply goes into the 1 battery. As a result, Option 1 statement of "losing the 140w" does not make sense. Option 2 will not help or hurt power efficiency but it will cause you to wire, monitor, and bms things differently.
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#6
I was under the impression that when u combine 2 arrays-pv panels and one of the panels (or in my case all the panels on 1 array) can’t produce as much power as the rest of the panels being combined with it then every panels specs essentially get lowered to the lowest panels specs.. this is where the 140w loss is combining from if I combine the arrays..
Yes Ik I do not lose 140w if I used 2 separate charge controllers.. but option 1 is using 1 charge controller which would give me 140 watts less than the arrays staying separate and then connected to their own charge controller.

Wouldn’t using 2 charge controllers mean that my system would have the efficiency loses of having both of the charge controllers loses, considering that every charge controller has efficiency losses then adding another charge controller would add its efficiency loss to the system aswell
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#7
(09-27-2019, 11:13 PM)Doin it Wrote: I was under the impression that when u combine 2 arrays-pv panels and one of the panels (or in my case all the panels on 1 array) can’t produce as much power as the rest of the panels being combined with it then every panels specs essentially get lowered to the lowest panels specs.. this is where the 140w loss is combining from if I combine the arrays..
Sorry - I was focused on the notion that 2 batteries (instead of 1 battery) would save you the 140w.    

As far as combining pv arrays - I can't advise you on that as the details matter and 140w out of 3000w is so small it might be hard to prove one way or another.    I would agree that if 2 controllers are convenient, it would be fine to have 2 of them.    Suggest you review some youtubes such as this one "What’s worse? Mismatched solar panels with different amps in series or parallel?"  https://youtu.be/P3YtBrymJdA  or this one  "How to Wire Mismatched Solar Panels in series and parallel"  https://youtu.be/vj_VyVmCSQU  and it might help you reach a decision.
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#8
Let me rephrase.. Ik if I combine both of my arrays that the total output of the combined arrays would be less than if I kept the arrays separate.. due to lower watt panels bringing the rest of the panels production down.. I’ve watched those YouTube videos..
I guess I just have to weigh the 2 charge controllers vs 1 charge controllers efficiency.. and weigh combining arrays and getting the 140w loss vs keeping them separate ..
Like u said using one (combined battery) or keeping them separate shouldn’t be more efficient one way or the other
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#9
Panels in a series string that are shaded, or cells in a panel that are shaded will bring down the output of that series string.

Strings in parallel will make what they will make, regardless of the shading of the other parallel strings.

I have a 4s, 3p setup. One array faces a bit more east, one a bit more west and the middle one faces due south. All feeding a single outback flexmax60
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#10
Either will work, but having a separate MPPT tracker on each PV string will likely produce a bit more power. Potentially quite a lot more if you have partial shading on your roof.
The devices don't even need to be the same make/model.

Having both chargers feed the same lithium battery is not a problem at all, in fact it will be better because the work will be spread among all cells, thus decreasing stress on the cells and increasing their life. Of course, the battery has to be able to safely take in the combined maximum power of each charger.

Having 2 inverters draw from the same battery is also not a problem.

You may want to have a look at my setup: multiple pv strings, multiple chargers, 1x battery (in 4 strings), multiple inverters.
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