Help Combining Panels (pics)

Crash · January 2016

I would like some help in determining how, or even if, I should combine two panel sets I have installed on my motorhome and trailer. Just to give you an understanding of what I have, here is a picture of my setup.

As you can see from the photo, my 315 watt Solarworld panels are actually mounted on the rear door of my trailer, while I have two more Unisolar amorphous panels are on top of the motorhome.

I normally have the trailer with me, but occasionally travel with just the motorhome. I know I can use both sets of panels independently of each other, and that is what I currently do. But what I want to know is if I can, or should, combine them for more power when both the trailer and motorhome are connected. I have read of the drawbacks to combining different types of panels, but I am still a little confused as to if I could benefit from combining all of my panels as in the picture below.

I would like to know if these two panel sets are compatible in there outputs enough to justify combining them, or would this degrade the overall performance of the system?

I welcome your comments or suggestions.

zoneblue · January 2016

When combining panels in parallel what you are interested in is the Vmp. Getting that similar for each string is what allows the MPPT controller to find and use the MPP. In this case you have 73V for the monos and 66V for the amorphs. At 10% the difference should be near enough to work acceptably. Of course if you want absolute highest output youd use two controllers, but the worse that can happen is the tristar will choose one of the two Mpps and run the other string at a very slightly reduced effciency.

BTW you might also consider running these as 4 strings of 35V(ish) for your 12V system.

Crash · January 2016

Thanks zoneblue

The only reason I was trying to use 2 strings instead of 4 is to keep the cables at a minimum. I am trying to keep the voltage high, and amps low. Not sure that this is the best way to go, but seems to be working for now.

I am glad you think this set up will work. Here are the numbers I used, along with the calclations as I understand them. Hope this is correct?

Set A (2 x Solarworld Panels in series)

Watts 630

Amps 9.3

Volts 73

Set B (2 x Unisolar Panels in series)

Watts 272

Amps 4.1

Volts 66

Total (Set A + B Wired in parallel)

Watts 884

Amps 13.4

Volts 66

So I think I am going to get 884 watts out of a possible 902 watts. Seems reasonable to me if my math is correct.

Crash · January 2016

ooops! Correction on my numbers.

Set A (2 x Solarworld Panels in series)

Watts 630

Amps 8.7

Volts 73

Set B (2 x Unisolar Panels in series)

Watts 272

Amps 4.1

Volts 66

Total (Set A + B Wired in parallel)

Watts 845

Amps 12.8

Volts 66

So I think I am going to get 845 watts out of a possible 902 watts. Seems reasonable to me if my math is correct.

Darn, I hope this is right this time?

scrubjaysnest · February 2016

With your two banks of panels in parallel your voltage should be closer to the solarworld panels. When I had a 120 watt panel Vmp 16.9 volts in parallel with two 80 watt panels Vmp of 18.1 volts the system always ran at or close to the 18 volt Vmp panels. Of course at Imp of 7.5 and 9.4 amps the currents were much closer then your two strings.

Help Combining Panels (pics)

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