I have searched and failed to get any answer. When connecting 4 solar panels in parallel, how important is it to have the wires leading to a junction box equal length. ie; One panel would need 15 feet, while the last would need 8 feet. I will use 8AWG cables to the junction box and then two cables to the charge controller. I am thinking it would be best if all 4 panels had the same resistance to the junction box. Therefore all panels with15 feet of cable. What say you?
Wire lengths for solar panels. Where is GotSmart?
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MikeRuth
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I concur and would do the same, cut to fit as needed.
Update. My education. The voltage from solar panes will match to the lowest voltage panel. So I will make the longest run as short as I can. That will set the voltage drop. All the other panels will have shorter wires run as cleanly as needed.
Trebor English
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Longer wire than necessary on any panel will reduce the current available from that panel. Matching solar panel wire length doesn't matter. Each panel will have its current contribution reduced by its wire resistance. More wire, less current. Don't make any wires longer than necessary. If panel #3 gets a longer wire and contributes 4.8 amps instead of 4.9 amps that is not better. Panel #1 can still contribute 5.1 amps and it still doesn't make 4.8 amps from panel 3 better than the possible 4.9.
Longer wire costs more, weighs more, resists more. Don't deliberately make any wires longer than necessary.
Longer wire costs more, weighs more, resists more. Don't deliberately make any wires longer than necessary.
jimindenver
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Here is a voltage drop vs wire length calculator, one of many you can find.
http://www.calculator.net/voltage-drop-calculator.html
Basically the longer the wire the thicker it needs to be to carry the same current without loss. So you may find the need to use a thicker wire on the farthest panel or you may find that the loss is not worth worrying about.
http://www.calculator.net/voltage-drop-calculator.html
Basically the longer the wire the thicker it needs to be to carry the same current without loss. So you may find the need to use a thicker wire on the farthest panel or you may find that the loss is not worth worrying about.
frater secessus
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Trebor English said:
Placing the junction box where all the panels' cabling could reach it would sidestep the issue. I don't know if that's possible in OP's situation.
Consider this possibility: MPPT controllers will be driving the paralleled panels as a system. I can envision a scenario where the algorithm might run suboptimally if there was enough variation, causing a multiplication of the original power difference.. It would be a fun experiment to run if one had time.
If all of the panels are the same make, model, wattage, age, etc, and hooked up in parallel, then the panels will tend to self-level the output, assuming a balanced input of solar energy.
If your wire leads were so undersized that a few feet of length caused an imbalance, then the solution is to go up (larger) on wire gauge, not to add more wire length to the nearer panels.
Make sense?
If your wire leads were so undersized that a few feet of length caused an imbalance, then the solution is to go up (larger) on wire gauge, not to add more wire length to the nearer panels.
Make sense?
GotSmart
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This is a simple RV system, not a field of commercial panels.
Cut wires to fit, and run parallel as much as you can. If you will be carying more than 200W in panels, buy the 10G solar wire.
Simple 12V systems. You buy a good controler, and all you have you do is push buttons and clean the panels every two weeks. 6" or 3 feet wire difference does not matter in this case. You are not dealing with a symphony recording studio.
When running wires, I always mark the wires in several places as to + or -. It makes life much easier.
Cut wires to fit, and run parallel as much as you can. If you will be carying more than 200W in panels, buy the 10G solar wire.
Simple 12V systems. You buy a good controler, and all you have you do is push buttons and clean the panels every two weeks. 6" or 3 feet wire difference does not matter in this case. You are not dealing with a symphony recording studio.
When running wires, I always mark the wires in several places as to + or -. It makes life much easier.
Thanks. I appreciate the suggestions. I pretty much answered my own question. Help is always good here. I'm using 8 AWG from 100 watt panels. I was curious about balance but now realize it doesn't matter for power from panels.
This is an old old post and my problem was solved with more research. The question was if small differences in resistance would effect the output of solar panels, they being a more tender source than a chemical battery. Also; I found with experience it doesn't matter to my MorningStar if I disconnect the battery or solar first or last. So anyway I use a heavy duty double pole single throw switch and do them both with one twist.
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