How to combine a series panel array with a parallel panel array to a MPPT:

[Stonyman]

I'm in the process of designing a solar system for my camper. I would like to have a 2 panel portable series array that I could move around outside the camper to find the best sun. I would also like a 2 panel parallel array roof mounted to the camper (parallel to lessen negative affects of shading). My question is: How do I combine these two different arrays to a MPPT that only has input for a single array? is it as simple as using MC4Y2 Branch Connectors? Simply connect all 3 positive and all 3 negative (two connectors from the parallel array and the one from the series)?

Any and all help is appreciated.

 

[TomC4306]

I'm in the process of designing a solar system for my camper. I would like to have a 2 panel portable series array that I could move around outside the camper to find the best sun. I would also like a 2 panel parallel array roof mounted to the camper (parallel to lessen negative affects of shading). My question is: How do I combine these two different arrays to a MPPT that only has input for a single array? is it as simple as using MC4Y2 Branch Connectors? Simply connect all 3 positive and all 3 negative (two connectors from the parallel array and the one from the series)?

Any and all help is appreciated.

Overall voltage of the series array must match the voltage of the parallel array

 

[Stonyman]

Thank you for your reply Tom. Is there a simple way of combining the two arrays when the voltage does not match?

 

[TomC4306]

2nd mppt charge controller.

 

[Stonyman]

Thank you once again. I was hoping to use an all in one controller/inverter/charger like a Growatt or similar device. Is there a way of combining the two arrays before they enter the growatt? Something like a 2 string solar combiner box?

 

[Bud Martin]

What are the spec of the panels and the MPPT?

 

[Rocketman]

Just get another dedicated mppt
Here is the math on what you are asking…

100w Renogy panel as an example. 3 panels in each string.
Imp 4.91a
Vmp 20.4v

String 1 in parallel
Lowest volts - 20.4v
Add the Amps 14.73

String 2 in series
Add the volts - 61.2
Lowest amps - 4.91

Into their own mppt they will each produce 300w
20.4 times 14.73 = 300w
61.2 times 4.9 = 300w

Now if you combine those two strings (this is the same process as combining different sized/electric spec solars panels.

Combined in parallel
Lowest volts - 20.4
Add the amps 19.64
Giving 400w for the system. You lost 2 panels.

If your Growatt has two separate mppt channels- then one string in each Chanel. If not one string into the Growatt and the second string into a separate mppt that connects directly to the battery.

 

[MisterSandals]

Is there a simple way of combining the two arrays when the voltage does not match?

All the responses above are good and helpful.

Looking at this differently, you are probably more constrained by your rooftop panels. Do you have any panels in mind for your rooftop?
From there, you may be able to find deployable panels that you can configure and match with your rooftop array (and combine in parallel before your inverter). Or are there significant constraints with your deployable array?

So locate (not necessarily buy) rooftop panels that fit first. Then see if its possible to make a deployable array.

 

[Stonyman]

Thank you all for your help. It is very much appreciated.

The system I envision would use a Growatt SPF3000TLLVM-24P. It only has one MPPT.
SpecsV input 2000w
Max solar charge current 80A
Max VOC 145 VDC
MPPT 30VDC-115VDC

Panels (4) 250W
VOC 37.6
VMP 30.3
8.27 Amp

This system would be located inside a camper here in Canada and due to the extreme cold in the winter it the electronics could not be stored inside over the winter. Therefor, It would have to be very portable. Hence why I'm looking at the Growatt. One device, easy in and easy out.

As for the panels. A portable series array is optimal for my needs. I do a lot of back country camping in areas with fairly dense foliage. A 2-3 panel series array, which I can locate a ways (30 ish feet) from the camper and easily (ish) relocate as needed during my stay. There is not a lot of room on the camper roof to locate panels. I think I could squeeze 2 up there. I would like them in parallel to minimize the affect of shading on them. These extra panels would help to maximize the charging potential of the system.

Option 1
single series 3 panel array : 37.6x3=112.8 @8.27A = 933.6 Watts

Option 2
Series array: 2 panels 37.6x2=75.2V @ 8.27A = 621.9W
Parallel array: 2 panels 37.6V @ 16.54 A = 621.9W
1243.8 W total
I was hoping for a device that would combine the 2 different arrays together(option 2) and then be able connect directly to the MPPT. It seems that such a device does not exist or does it?

https://solarpowercombinerbox.com/p...-with-circuit-breakers?variant=32459047206971

A 2 sting version of this combiner box with 2 20A breakers rated for 150V. Is it possible to have each string connect to a it's own 20A breaker then have this connected to the MPPT? It would make 112.8VOC and 24.81A total watts 2798.5W. Well within the parameters of the MPPT and since each string has its own 20 breaker it would not overload the combiner box either. My knowledge of this subject is quite limited but it seems feasible to me.

Thank you all again for all your help.

 

[MisterSandals]

Panels (4) 250W
VOC 37.6

You are pretty much limited to 2S2P configuration. This creates 75.2V array
This requires a pair of MC4 Y connectors.

There are a lot of panels that are in the 37Voc range so having a deployable array with
2 (series) or 4 (2S2P) of these would be perfect.

Option 2
Series array: 2 panels 37.6x2=75.2V @ 8.27A = 621.9W
Parallel array: 2 panels 37.6V @ 16.54 A = 621.9W
1243.8 W total

This does not work. I have no idea why one would make 2 arrays this way to combine them.
And, if you have 250W panels, they are only going to produce 250W no matter how you combine them.

Is the 8.27A you are using the Isc (short circuit current) or the Imp (working current)?

Should be 250W / 30.3Vmp = 8.25Imp

 

[Bud Martin]

Thank you all for your help. It is very much appreciated.

The system I envision would use a Growatt SPF3000TLLVM-24P. It only has one MPPT.
SpecsV input 2000w
Max solar charge current 80A
Max VOC 145 VDC
MPPT 30VDC-115VDC

Panels (4) 250W
VOC 37.6
VMP 30.3
8.27 Amp

This system would be located inside a camper here in Canada and due to the extreme cold in the winter it the electronics could not be stored inside over the winter. Therefor, It would have to be very portable. Hence why I'm looking at the Growatt. One device, easy in and easy out.

As for the panels. A portable series array is optimal for my needs. I do a lot of back country camping in areas with fairly dense foliage. A 2-3 panel series array, which I can locate a ways (30 ish feet) from the camper and easily (ish) relocate as needed during my stay. There is not a lot of room on the camper roof to locate panels. I think I could squeeze 2 up there. I would like them in parallel to minimize the affect of shading on them. These extra panels would help to maximize the charging potential of the system.

Option 1
single series 3 panel array : 37.6x3=112.8 @8.27A = 933.6 Watts

Option 2
Series array: 2 panels 37.6x2=75.2V @ 8.27A = 621.9W
Parallel array: 2 panels 37.6V @ 16.54 A = 621.9W
1243.8 W total
I was hoping for a device that would combine the 2 different arrays together(option 2) and then be able connect directly to the MPPT. It seems that such a device does not exist or does it?

https://solarpowercombinerbox.com/p...-with-circuit-breakers?variant=32459047206971

A 2 sting version of this combiner box with 2 20A breakers rated for 150V. Is it possible to have each string connect to a it's own 20A breaker then have this connected to the MPPT? It would make 112.8VOC and 24.81A total watts 2798.5W. Well within the parameters of the MPPT and since each string has its own 20 breaker it would not overload the combiner box either. My knowledge of this subject is quite limited but it seems feasible to me.

Thank you all again for all your help.

Vmp x Imp = panel Wattage.

 

[TomC4306]

Thank you once again. I was hoping to use an all in one controller/inverter/charger like a Growatt or similar device. Is there a way of combining the two arrays before they enter the growatt? Something like a 2 string solar combiner box?

If you're okay buying a solar combiner box, a mid-tier mppt doesn't cost any more than that.
Do it right.

 

[Stonyman]

You are pretty much limited to 2S2P configuration. This creates 75.2V array
This requires a pair of MC4 Y connectors.

There are a lot of panels that are in the 37Voc range so having a deployable array with
2 (series) or 4 (2S2P) of these would be perfect.

This does not work. I have no idea why one would make 2 arrays this way to combine them.
And, if you have 250W panels, they are only going to produce 250W no matter how you combine them.

Is the 8.27A you are using the Isc (short circuit current) or the Imp (working current)?

Should be 250W / 30.3Vmp = 8.25Imp

Thank you all once again. Panel is 8.27A max power current and 8.85 ISC I misread the panel. The 2S2P solution seems to be the best option for me. I could also buy a second Mppt as mentioned as well. Thank you all. Happy New Year!

 

[MisterSandals]

The 2S2P solution seems to be the best option for me. I could also buy a second Mppt as mentioned as well.

Assuming that the 2S2P array is on the roof, you could easily add a 2S deployable array whenever you want it.
If you put an extra MC4 Y connector anywhere in your wiring between the 2S2P array and your charge controller, adding the deployable array will be just a matter of plugging into the Y connectors. Your existing array can easily handle 6x 250W panels. This would be a very nice setup.