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Open Roads Forum  >  Tech Issues

 > Question about solar combiner box.

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EMD360

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Posted: 08/09/21 07:41am Link  |  Quote  |  Print  |  Notify Moderator

I’m designing a small solar system for the RV roof. I have room for 3 100 watt panels which I have already ordered from Northern Arizona Wind and Sun. I know this company from when I lived in Arizona and have confidence they stock quality materials at reasonable prices. The panels are 52x20 so they can be shipped UPS.
I can’t wire 3 panels in parallel and I want the panels to be shade tolerant. I’m considering wiring them individually to a combiner box on the roof. I can’t find information about this wiring setup. I assume it would be the same as using a combiner box for more than one string. Each panel would be its own string. So has anyone wired their panels like this? Does it make sense to keep them as separate “strings”?


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2oldman

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Posted: 08/09/21 08:13am Link  |  Quote  |  Print  |  Notify Moderator

Series wiring is much easier. Bypass diodes make them shade tolerant -not that you want to be in the shade much.

agwill

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Posted: 08/09/21 08:40am Link  |  Quote  |  Print  |  Notify Moderator

A combiner is just putting all three in parallel how ever you do it and it takes more wire. There are all types of connectors to hook up anyway you want. I changed to series and that allows for a smaller wire hookup to your controller. You need a higher voltage input controller and there are plenty that allow 100 volt input. MPPT is what you want and it gives better charging.


al

Lwiddis

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Posted: 08/09/21 09:41am Link  |  Quote  |  Print  |  Notify Moderator

I use a combiner box under one of my three 100 watt panels. Easy…works. No reason IMO to run three strings to the controller. With three panels how can OP wire in series?


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CA Traveler

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Posted: 08/09/21 10:45am Link  |  Quote  |  Print  |  Notify Moderator

The purpose of a combiner it to wire panels in parallel. If you wire serial you don't need a combiner.

For serial run controller wire to panel 1, panel 1 to panel 2, panel 2 to panel 3 and panel 3 to the controller. Make sure your panels have bypass diodes if you want the maximum shade tolerance.


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Posted: 08/09/21 10:52am Link  |  Quote  |  Print  |  Notify Moderator

Rereading your post and there may be a misunderstanding - To be clear: Serial panels with bypass diodes are more shade tolerant than parallel panels and are used with a MPPT controller.

There are incorrect posts that don't understand bypass diodes and state the parallel panels are more shadd tolerant.

2oldman

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Posted: 08/09/21 11:07am Link  |  Quote  |  Print  |  Notify Moderator

..

pianotuna

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Posted: 08/09/21 11:13am Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

Rereading your post and there may be a misunderstanding - To be clear: Serial panels with bypass diodes are more shade tolerant than parallel panels and are used with a MPPT controller.

There are incorrect posts that don't understand bypass diodes and state the parallel panels are more shadd tolerant.


Hi CA Traveler,

Can you provide a link that agrees with your statement?

The ideal panel would have bypass diodes on each cell. I've found one company in Germany that makes one--but I can't find anyone who is selling them. My existing Uni-Solar panels do have that feature.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

CA Traveler

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Posted: 08/09/21 12:39pm Link  |  Quote  |  Print  |  Notify Moderator

There have been many posts on bypass diodes and how they improve shaded panel performance. Here are posts by time2roll and me showing how bypass diodes work. http://www.rv.net/forum/index.cfm/fuseac........d/29633200/gotomsg/29633722.cfm#29633722

http://www.rv.net/forum/index.cfm/fuseac........d/29633200/gotomsg/29709584.cfm#29709584
I adopted this graphic from Solar Professional which may still have archives available.

And 3 posts earlier from my post is a graph of my real world solar output in leafy shade with bypass diodes.

And this thread contains some incorrect statements or understanding of bypass diodes.

2oldman

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Posted: 08/09/21 12:43pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:


And this thread contains some incorrect statements or understanding of bypass diodes.
I don't see them.

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