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Old 07-15-2013, 05:09 AM   #1
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Solar panel wiriing

I intend to install a solar system next week and have a question about wiring the panels. What is the best arrangement....wiring the panels to each other and then sending one wire thru the roof to the controller or sending two wires, one from each panel, to the controller?

The system will include 2 Kyocers 140's, and a Big Sky 2000E 25 amp MPPT controller. The runs are 6ft from roof to controller and 8ft from controller to 4 6v wet cell batteries. I plan to use 6 gauge wire for everything.
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Old 07-15-2013, 05:38 AM   #2
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Wire the 2 panels in parallel (to minimize shading losses) to a combiner / junction box on the roof. Then a single wire pair from the combiner / junction box to the controller. This also makes it easier to add more panels later, uses less wire, is more efficient, etc.

I would also suggest larger wire coming down from the roof than #6 to reduce loss and provide for adding more panels later without having to rewire..
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Old 07-15-2013, 05:54 AM   #3
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Quote:
Originally Posted by vsheetz View Post
Wire the 2 panels in parallel (to minimize shading losses) to a combiner / junction box on the roof. Then a single wire pair from the combiner / junction box to the controller. This also makes it easier to add more panels later, uses less wire, is more efficient, etc.

I would also suggest larger wire coming down from the roof than #6 to reduce loss and provide for adding more panels later without having to rewire..
Good advice.....many thanks!
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Old 07-15-2013, 09:47 AM   #4
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One of the advantages of MPPT is that you can have a higher Voltage from the panels than what your battery's are wired for.

I'd suggest wiring in series for 24 volts to the controller, which will provide 12 volts to the batts, increasing proficiency.


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Old 07-15-2013, 09:55 AM   #5
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Higher voltage from the combiner box is better, as that's less amps and less voltage loss on the wiring run.
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Old 07-15-2013, 10:24 AM   #6
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#6 wire is overkill. The resistance of #6 wire is .3951 ohms per 1000 ft. so at 10 feet the resistance would be .00395 ohms. If you got the max of 25 amps from the panels and hopefully you do on some really bright days, then the voltage drop over 10 feet would be .
.0989 Volts with #6 wire.

Here is a link to a chart with the resistance included for wire sizes American wire gauge - Wikipedia, the free encyclopedia using only what you need will save you money and make it look better, but just as important it will be a lot easier to pull the wire.

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Old 07-15-2013, 02:37 PM   #7
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I question the series wiring for these panel in this scenario vs. parallel wiring. Agree with the higher voltage efficiencies of serial wiring, but in this scenario with these panels that is not that big a upside when compared to the losses when a shading situation is encountered. Most solar systems can perform well in full sunlight, excellent conditions - but also what matters is how well it will perform in marginal situations.
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Old 07-30-2013, 09:22 PM   #8
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Quote:
Originally Posted by vsheetz View Post
I question the series wiring for these panel in this scenario vs. parallel wiring. Agree with the higher voltage efficiencies of serial wiring, but in this scenario with these panels that is not that big a upside when compared to the losses when a shading situation is encountered. Most solar systems can perform well in full sunlight, excellent conditions - but also what matters is how well it will perform in marginal situations.
AMSolar is a well respected company specializing in RV solar system design and installation. Here are design comments from their web site supporting the usage of panels wired in parallel.
Designing your RV Solar Battery Charging System for Real World Conditions
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Old 07-31-2013, 11:40 AM   #9
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You have lot's of real estate on top of that roof. If you decide you want to add more panels in the future, you may wish you had gone with a large capacity Controller. A 60 Amp MPPT will cost you a bit more now, but will also allow you to add more panel capacity in the future. IMO, also buy a combiner box with extra capacity for future added panels. Lastly running wire can be a real PITA, so while smaller gage runs may support your current needs, if you ever decide to add more panels, having a bit thick gage installed now will allow future upgrades too...

Another thought, that you may already be doing, to get the most out of the smaller size solar panel, you may find tilting bars a good thing to consider. (I hate getting up on the roof, and will hate it more in the years ahead. So though I'll add tilting bars (AM Solar's - Great site for overall reading and education, and good products too), my goal is to not need them from oversizing the panels watts available.)

One other tip that was carefully 'suggested' to me, is the addition of a good Battery Monitoring system meter. It allows you to see what is going on, and learn how you use energy and how well your various battery charging methods are working/supporting your actual needs.

Besides AM Solar, Jack Mayers has a good site that include Solar Panels info within it.

I wish you luck, and be safe!
Smitty

(FYI - Our SP system as it is planned now includes: 4 X Panasonic HIT 240 s panels, Midnight Classic 150 Lite Controller, AM Solar Combiner box, AM Solar tilt bars, etc.)
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