PV same length wiring, how?

[Kwest364]

Wiring from panels on roof, how do people keep wire runs same length to avoid V drop?

Already have solar set up, but needs updated wiring, bigger size, and cleaning up.

I'll be running 10 gauge wire on roof, to roof gland above driver seat (outside bus) to inside, down to floor and run to just behind driver seat (where battery bank is). 6x185W panels, running length wise. Panels towards front of bus will have shorter cable, vs rear panels will need longer cable (attached pic). How do people mitigate this?

Doesn't matter? Overthinking it? Just run different lengths and call it a day?

 

[Ozbozz57]

What I did was run all the wires (10 ga) to a roof-mounted waterproof box near the panels. I have six panels, "180 watt" 36 cell, "12 volt" nominal. There's a max of about 3-4 feet difference in panel-to-box wire length between the rear row of panels and the front row, but all the wires are short, and with 10 ga wire, the voltage drop, and the difference between the runs is negligible. For safety overkill, each panel is fused 15 amps inside the collector box, and they are grouped into two groups of three. Each group feeds down into the bus via 6 ga wires, which are also fused.

 

[nikitis]

This matters more with thicker gauge wire. Like from Batteries to inverter. And it's not from a matter of voltage drop, as it is the inverter always drawing more from the battery with the shortest cables which means it pulls more power cycles more often from that battery than from batteries with longer cables.


From roof to PV Combiner, a small difference in length of a few feet aren't going to matter at all if you are using a thinner gauge wire. To see a voltage drop you'll really need a length of like 20ft vs 40ft. Much under 20ft should be fine.


Examples from Solar Panel to PV Combiner:
Lines that are 10ft vs 20ft, not going to see a difference that matters in anyway.



Lines that are 10ft vs 40ft, you may measure a small difference, but still not terrible, and is acceptable.


Lines that are 10ft vs 100ft, yeah you'll notice it.


Examples from battery to inverter:
A 3ft line for one battery and a 4ft line to the inverter, is acceptable but still can pull from one battery more, just not enough that it's going to wear the 3ft battery out much sooner than the 4th.


A 3ft line for one battery and a 5ft line to the inverter, is starting to get far worse, and will begin to drain the 3ft line battery more often than the 5ft line battery over time and will die a few months sooner than the others.


If you can equalize the length to the inverter from the batteries they'll all wear evenly as they will all be drawn from evenly.



It's more important to keep the battery lines as close as length the same as you can than it is for the Solar panels to reach the PV Combiner. This is usually impossible, but you can get close so don't beat yourself up about it if you cannot do it exactly, but it's important to plan it out first before cutting your cables and crimping them.


This is also a good reason to rotate your batteries after a year or half a year.


Another thing, from your picture, I see you have your panels at two different angles. Angles matter. Best absorption is going to occur if the panels shoot directly at the sun perpendicular from the direction of the light. This is not really doable for most buses as you'd require a frame that is adjustable for the angle. But you can put larger mounts on the outside to make them flat. You'll get uneven absorption having panels at two different angles and wont' maximize your solar sun energy collection. I'd make them flat so the panels are at the same angle at least. Aesthetically it looks nicer the way you have them but you are probably losing 10-20% absorption capability with the way you have them. If they are flat you'll get more out of them.