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Combine separate arrays or not
#11
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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#12
(09-28-2019, 02:13 PM)Doin it Wrote: 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?

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 the  MPPT 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.
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#13
I think I’d 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 that’s 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 shouldn’t have said 4 wires to one controller
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#14
(09-28-2019, 04:08 PM)Doin it Wrote: I think I’d 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 that’s  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 shouldn’t have said 4 wires to one controller

Great!   Sounds like you have enough info now to make sound decisions for your situation.  That's what its all about for DIY Smile
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#15
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 wouldn’t want the mppt controller acting goofy not being able to find the true mpp, due to 2 arrays being combined into one.
Also wouldn’t 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.
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#16
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 I’m asking about the volts.
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#17
(09-29-2019, 04:37 PM)Doin it Wrote: 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 I’m asking about the volts.

Here's a detailed discussion with pictures/examples of series/parallel wiring of panels the same and with different characteristics  https://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 lost 1,138kwh (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/saving 716kwh of those 1138kwh lost...    but I haven't, because 'its complicated' Smile

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.
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#18
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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#19
(09-29-2019, 08:20 PM)Doin it Wrote: 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?
>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 electrical logic 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.
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#20
I guess I’m 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..
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