Combine separate arrays or not

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 Id 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..

Whats the reason for no one commenting.. is there more information needed?

Doinit said:

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 Id 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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>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 muchpowerfor 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 orbecause wiring (to a common physical location) might not make sense or just because you want to.

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 Im 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 Id 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 Im 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..
Whats the pros and cons of each option?

Doinit said:

Having 2 controllers charging the same battery bank might cause confusion (maybe just in my brain) somehow idk.. Ik it can be done but Id 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 Im 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..

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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. Youdescribe 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 have1 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. Thereis no power efficiency in having 2 batteries as apposed to 1.

Doinit said:

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..
Whats the pros and cons of each option?

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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'tloose 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.

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) cant 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.

Wouldnt 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

Doinit said:

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) cant 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..

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Sorry - I was focused on the notion that2 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 behard 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 "Whats worse? Mismatched solar panels with different amps in series or parallel?" or this one"How to Wire Mismatched Solar Panels in series and parallel" it might help you reach a decision.

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.. Ive 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 shouldnt be more efficient one way or the other

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

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.

Shading is not an issue but all of one of the arrays panels are lower specs so they might aswell be partially shaded compared to the other array-panels..
Ok so as long as I keep the lower producing panels-array from being series to the higher producing panels-array then I will get the total amount of power the panels are producing now being two separate arrays? Even if they all will be connected to one mppt?
Right now the lower spec panels-array are wired 3s2p for 99v 20amps, and the other separate higher spec array is the wired the same.. this gives me 4 wires, 2 of the wires going to each inverter, no charge controllers or batteries yet.. if I was going to use one charge controller then I was either going to combine those 4 wires in parallel with a bus bar or wire the 4 wires directly to the charge controller in parallel..
So are u guys saying that using one charge controller-mppt will not lower the production of the higher spec array to match the lower spec array?

Doinit said:

Shading is not an issue but all of one of the arrays panels are lower specs so they might aswell be partially shaded compared to the other array-panels..
Ok so as long as I keep the lower producing panels-array from being series to the higher producing panels-array then I will get the total amount of power the panels are producing now being two separate arrays? Even if they all will be connected to one mppt?
Right now the lower spec panels-array are wired 3s2p for 99v 20amps, and the other separate higher spec array is the wired the same.. this gives me 4 wires, 2 of the wires going to each inverter, no charge controllers or batteries yet.. if I was going to use one charge controller then I was either going to combine those 4 wires in parallel with a bus bar or wire the 4 wires directly to the charge controller in parallel..
So are u guys saying that using one charge controller-mppt will not lower the production of the higher spec array to match the lower spec array?

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Let me go out on a limb just a bit here and share what I've learned (but have not actually done this personally).

When you hook two batteries (*of the same voltage*) together in parallel resulting amps are the addition of the 2 batteries. Its the same for panels - when you hook to panels (pv arrays in your case) together in parallel with *same voltage* then its the addition of amps from both arrays - i.e. no power is lost. In the battery case current will flow between the parallel batteries and the voltage will equalize - so they will have the same voltage. In the panel case, this can't happen - so the panels must produce the same voltage independently... thru-out the day (lower/higher sunlight)... *at the same exact moments thru the day*. This is where shading comes in as a shaded pv array will have a different voltage curve than the non-shaded pv array - even if the panels are identical.

If the panels have an exactly similar voltage curve based on sun going higher/lower thru the day - the the amps will be additive with no loss and 1 controller will be same as 2 controller in overall output. However, if one array has slightly different voltage than the other - then 'fuzziness' can come into the picture when theMPPT tries to find the exact optimum voltage/amps of both combined.

If you have 2 arrays and 2 controllers - the difference between pv arrays doesn't matter. If you have 1 controller and combine the strings its OK, but there 'might be' some fuzziness and loss of power. You have to weight this against the cost of a 2nd controller etc... and the % of fuzziness / potential loss. Its not wrong to loose 5% of your power (140w/3000w)its a matter of $ and design and your personal goals. This is why its ultimately up to you to make the decision.

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>I was either going to combine those 4 wires in parallel with a bus bar or wire the 4 wires directly to the charge controller in parallel..
If you go with 1 controller - then you typically add a 'combiner box' with circuit breakers. This is where you hook the array wires in parallel. Then from the combiner box, you run 2 wires out to the 1 controller. The combiner box contains the 'bus' and the circuit breakers allow you to turn 1 or the other or both 'off' so you can disconnect the power from the pv arrays as you work on t he controller.

I think Id rather lose the extra 100$-200$ upfront by purchasing an extra charge controller, than instead losing roughly 140w for the life of the system, if thats what will happen if I combine the arrays due to mppt of the single charge controllers fuzziness
Yeah I would (if using one charge controller) wire all 4 wires to a bus bar and breakers (already have breakers installed) to mimic a combiner box.. I shouldnt have said 4 wires to one controller

Doinit said:

I think Id rather lose the extra 100$-200$ upfront by purchasing an extra charge controller, than instead losing roughly 140w for the life of the system, if thats what will happen if I combine the arrays due to mppt of the single charge controllers fuzziness
Yeah I would (if using one charge controller) wire all 4 wires to a bus bar and breakers (already have breakers installed) to mimic a combiner box.. I shouldnt have said 4 wires to one controller

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Great! Sounds like you have enough info now to makesound decisions for your situation. That's what its all about for DIY

Maybe this has been covered sorry if it was..
If I was going to use one charge controller, having the 2 arrays combined in a combiner box etc. Would this give the mppt of the single charge controller a hard time due to it trying to mppt 2 separate arrays, therefore having less production than if I had each array had its own controller? Or does the mppt really just use the total power coming to its terminals and mppts that power as if it was one array?

I could rewire both arrays together on the roof and have just 2 wires (not needing combiner box) but I do not think my panels could handle the 40amps that would be created by doing this. Also doing it this way would require heavier wires (2 wires) run from panels all the way (50 ft) to the charge controller. But if my panels could handle that amperage and I used heavier wire for the long run, would this make the mppt of the charge controller work more efficiently-effectively than having 2 separate arrays (4 wires) being combined to have 2 wires going to the charge controller? I wouldnt want the mppt controller acting goofy not being able to find the true mpp, due to 2 arrays being combined into one.
Also wouldnt combining the arrays in a combiner box (in parallel) automatically lower the possible production of the higher volt panels-array to what the lower array-panels could produce(or close).. due to the basic knowledge of combining 2 different amp panels (my case 2 arrays) in parallel causes the higher volt panel-array to be lowered to the volts of the lowest volt panel- array.

If I combine both arrays together in parallel in a combiner box and the arrays specs are slightly different, and one array produces les than the other, Will the higher producing arrays volts get dropped to the lower producing arrays volts?..
The amps of both arrays would just get added together when wiring them together in parallel in combiner box.. but Im asking about the volts.

Doinit said:

If I combine both arrays together in parallel in a combiner box and the arrays specs are slightly different, and one array produces les than the other, Will the higher producing arrays volts get dropped to the lower producing arrays volts?..
The amps of both arrays would just get added together wiring then together in parallel in combiner box.. but Im asking about the volts.

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Here's a detailed discussion with pictures/examples of series/parallel wiring of panels the same andwith different characteristicshttps://solarpanelsvenue.com/mixing-solar-panels/
Examples of how calculating the amount of loss are included.

A mismatch will result in loss but its not wrong, its a question of how much loss vs other considerations - especially in your case where you indicate the different arrays are 'very close'.

I'll give you an example of loss vs $. My inverter is a cheaper AIMS that says its 88% peak efficient. Overall this year so far, I've averaged 86.5%efficiency in converting DC to AC according to my measurements. This means that out of the 8,432kwh I've produced by my PV array, I've lost1,138kwh (13.5%). That's a huge amount of power!! I could try to re-sell / decommision my AIMS and spent $$ on a couple of Magnums which promise 95% efficiency with the goal of getting back/saving716kwh of those 1138kwh lost... but I haven't, because 'its complicated'

My personal advice is to not worry about 140w (out of 3000w) loss so much as just make sure you don't back yourself into a corner or do anything unsafe. For example, you can hook both PV arrays in parallel today and then get a 2nd controller next month as budget allows.

Offgrid.. I understand what would happen when combining individual panels in every way they could be combined...
My question is if the same would happen when wiring 2 arrays together instead of individual panels? Wiring the 4 wires from 2 arrays in parallel to have just 2 wires to connect to the single charge controllers terminals, would mean that the total amperage of both arrays would just get added together but the total volts of the arrays would be knocked down to the volts that the lowest array had?

Example: 1st array- 97v 18amps
2nd array- 99v 20amps
I think if I combine those 2 arrays in parallel (4 wires turned into 2 wires) to one charge controller that the charge controller (at max solar output) would see 97v 38amps.. is that correct?

Doinit said:

Offgrid.. I understand what would happen when combining individual panels in every way they could be combined...
My question is if the same would happen when wiring 2 arrays together instead of individual panels? Wiring the 4 wires from 2 arrays in parallel to have just 2 wires to connect to the single charge controllers terminals, would mean that the total amperage of both arrays would just get added together but the total volts of the arrays would be knocked down to the volts that the lowest array had?

Example: 1st array- 97v 18amps
2nd array- 99v 20amps
I think if I combine those 2 arrays in parallel (4 wires turned into 2 wires) to one charge controller that the charge controller (at max solar output) would see 97v 38amps.. is that correct?

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>would see 97v 38amps.. is that correct?
Yes This is one of the examples in the link provided earlier. 2 arrays in parallel is the same electricallogic as 2 panels in parallel

If your controller is OK to handle 97v*38a = 3686watts - then you can test this yourself by hooking 1st array and recording PV1-watts (97v*18a=1746w), then 2nd array and recording PV2-watts (99v*20a=1980w) and then both together and see if the combined watts = PV1-watts+PV2-watts. This will give you actual data as to loss.

I guess Im just going to get an outback 60 or 80 and just hook up one of the arrays to it for now and leave the other straight grid tie for now.. The controller will be able to handle the total of both arrays when I get a bigger battery bank.. for now with my small battery module I do not want more than 30 amps charging it anyways.. thx for all your help..