mixing qty of panels in series groups?

[justinm001]

this is on an RV roof. I currently have 2 parallel groups of 5 panels in series and am adding an additional 6 panel group. All are the exact same Renogy 100w panel with info below. All plug into a Victron 150/100 MPPT. Does it matter that one group will have a potentially higher voltage than the rest? Also since the roof is pitched a bit, 1 group is on the rear drivers side, other group is on rear passengers side and the new group will be half and half on the front. Not sure if this affects anything but the RV moves around so sun could be hitting different groups at different times.

I've never got near 1000w yet on these panels and most is around 550w. I plan on putting a total of 1800-2000w even though the MPPT is only rated for 1450w.

Max Power at STC	100 Watts
Open Circuit Voltage	24.3 V
Short Circuit Current	5.21 A
Optimum Operating Voltage	20.4 V
Optimum Operating Current	4.91 A
Cell Efficiency	22.00%
Operating Temperature	-40°F to 176°F(-40℃ to +80℃)
Dimensions	41.8 x 20.9 x 1.4 in (1062 x 530 x 35 mm)

 

[sunshine_eggo]

this is on an RV roof. I currently have 2 parallel groups of 5 panels in series and am adding an additional 6 panel group. All are the exact same Renogy 100w panel with info below. All plug into a Victron 150/100 MPPT. Does it matter that one group will have a potentially higher voltage than the rest?

Yes. You must not do this. You will notably compromise your array performance to well under what you would lose if you just add 5 panels for 5S3P. In other words a 5S2P string in parallel with a 6S string will perform way worse than a 5S3P array.

The Vmp/Voc values of each string need to be within 5-10% for consistent operation, and you will see a 5-10% performance penalty on all strings. Make it larger than that, and you will almost certainly disrupt the MPPT function, fail to get anywhere near rated power AND the lower voltage strings may serve as short circuit pathways for the high voltage string, so the MPPT never sees any voltage/current at all.

 

[justinm001]

Yes. You must not do this. You will notably compromise your array performance to well under what you would lose if you just add 5 panels for 5S3P. In other words a 5S2P string in parallel with a 6S string will perform way worse than a 5S3P array.

The Vmp/Voc values of each string need to be within 5-10% for consistent operation, and you will see a 5-10% performance penalty on all strings. Make it larger than that, and you will almost certainly disrupt the MPPT function, fail to get anywhere near rated power AND the lower voltage strings may serve as short circuit pathways for the high voltage string, so the MPPT never sees any voltage/current at all.

Thanks for this. I just got the additional panels and have more room than expected so ordered 4 more so I'll have 5S4P.
But more to your point, my panels aren't at identical angles, and furthermore because it's in motion and parked in various spots it is very likely some would be shaded by a tree or something else. Wouldn't this effectively cause the same issue? Do I need to get multiple smaller MPPTs and not have them in parallel?

 

[sunshine_eggo]

Thanks for this. I just got the additional panels and have more room than expected so ordered 4 more so I'll have 5S4P.
But more to your point, my panels aren't at identical angles,

Each string should be at the same angle. If not, all panels in the string will be current-limited by the lowest performing panel.

and furthermore because it's in motion and parked in various spots it is very likely some would be shaded by a tree or something else. Wouldn't this effectively cause the same issue?

No. The presence of light gives voltage. The intensity of light gives amps. shading impacts amps, but the voltage is barely affected. Thus, the Voc of the shaded string will be higher than the Vmp of the unshaded string.

Do I need to get multiple smaller MPPTs and not have them in parallel?

This would be the best approach if your strings can't be at the same angle. If you can get the 5 panels in the string facing the same direction, then the parallel strings may vary from one another without penalty, and you don't need individual MPPT.

Note that unless the angles are significant, the differences will be small. Do you have any examples?

 

[justinm001]

Each string should be at the same angle. If not, all panels in the string will be current-limited by the lowest performing panel.




No. The presence of light gives voltage. The intensity of light gives amps. shading impacts amps, but the voltage is barely affected. Thus, the Voc of the shaded string will be higher than the Vmp of the unshaded string.




This would be the best approach if your strings can't be at the same angle. If you can get the 5 panels in the string facing the same direction, then the parallel strings may vary from one another without penalty, and you don't need individual MPPT.

Note that unless the angles are significant, the differences will be small. Do you have any examples?

This makes a ton of sense thank you! It's only a slight angle. Just a bit disappointing that I'm getting so low performance. Attached is past 30 days and it shows in one day the max was just under 1kwh. I thought with 1000w I should be getting closer to 5kwh per day. It's been pretty gloomy and winter also I live in the woods but drive it around so I expected some days to be pretty good.

 

[sunshine_eggo]

You're only a few weeks out from the winter solstice. Northern hemisphere performance in winter can suck. Flat panels on an RV roof are only going to get 40-50% rated WITHOUT shading. Add shading, and it can be a turd sandwich.

 

[justinm001]

Awesome thanks. I'll see how 2k total panels work and I have room to easily add another 1k and 1200 on my trailer if needed

 

[littleharbor2]

As the sun's path rises with oncoming summer you should see improvments in performance. You do need to keep the RV on full sun to get this performance. Avoid shade wherever possible.