Solar and 12 AWG wiring

[rando]

The sidewall plug would just be in parallel with the combination of panels you have on the roof (so 36V based on the configuration earlier). You wouldn't want to use it with a nominal 12V (actual 17- 18V) panel, so you could disconnect it. The other option would be to move it to the battery (and add a fuse), so you could attach a portable panel with built in charge controller.

 

[radarcontact]

Thank you, Rando...you've been a big help. Deciding between convenience vs. ability to aim a portable. If I want it, I can get the 3rd rooftop panel cheaper than new from a friend who doesn't need his anymore...weight of the addl. 80W is not an issue (~15lbs.). I know I wouldn't have figured out the rooftop-only config. without your help, and Vic as well. Much appreciated.

If you have any final thoughts on series vs. parallel when using a MPPT controller I'd be interested...

 

[rando]

In your situation, I would think parallel would be best. The gains from series are small (couple %), the convenience of easier wiring and the use of a portable more than offset these gains.

 

[radarcontact]

I have read that a parallel connection is more efficient if either panel is partially shaded.

Camel, I thought about that, too, but my counter-argument to that is, if you have your panels all mounted on the roof of your camper, and they're all pointed in the same direction, it's probably rare that one will be in the shade and one in full sun, considering the fact that they're all in close proximity to each other. Possible, but not likely.

 

[Desert Scruff]

A while back when I was adding a 100-watt panel to the roof, in addition to the original 160-watt panel, I read on the Renogy website, in answer to a question about wiring in series, that Renogy did not recommend doing that unless the panels were of equal wattage, that doing so would pull the higher wattage panel down to the wattage of the lesser panel. When using unequal panels, Renogy recommended wiring in parallel. Unfortunately, I cannot furnish you a link to the question-answer.

 

[rando]

With the bypass diodes built into the panels the effect of shading is about the same in either series or parallel configuration.

To wire panels in parallel you want the voltages to be about the same, and to wire in series you want the currents to be about the same. Using the same wattage panels (from the same manufacturer) would probably mean both voltage and current are the same, but this isn't necessary.

 

[radarcontact]

Rando, could you elaborate a little on the shading aspects of parallel vs. series? Seems to be a lot of confusion out there regarding the two configurations. General consensus seems to be parallel is better in shade, bec. one panel in shade in series will draw the whole network down. Others say that, because of the higher voltages in series connections and the way MPPT controllers deal with that voltage, there is more usable voltage as the sun goes down to keep the current flowing. I read another post from an RVer who said that when they shaded part of one of their four panels with a piece of cardboard the whole array went to zero.....found that hard to believe, and not sure that's the norm. Don't know what you mean regarding bypass diodes..I'm guessing it's something built into the panel to work around short circuits between PV cells that aren't producing any voltage. I'll google that and read up on it.

 

[rando]

Bypass diode allow for current to flow around a panel (or even part of a panel as some panels have multiple internal bypass diodes) that is shaded and not producing any current. So shading one panel in a series string will mean that the current is bypassing that panel through its bypass diode, and therefor it is not adding any voltage to the string, but it still conducts current and therefore the string should be close to its nominal current.

To give an example - say you have four 100w panels (5A at 20V) - in series they produce 80V at 5A, and in parallel they produce 20V at 20A. If you shade one series panel, you end up with 60V at 5A, or if you shade one parallel panel you end up with 20V at 15A - so about the same power in both situations. Things get more complicated if you are partially shading multiple panels, but there is no clear winner as to which configuration does better/worse in shade.

 

[PaulT]

I found this video interesting about series vs parallel. Still requires a value judgement re: your situation, but some interesting data points.

https://www.gonewiththewynns.com/Sailboat-Solar-Series-Parallel-Shading

Paul

 

[radarcontact]

I found this video interesting about series vs parallel. Still requires a value judgement re: your situation, but some interesting data points.

https://www.gonewiththewynns.com/Sailboat-Solar-Series-Parallel-Shading

Paul

I saw that too, Paul...I think I've scoured every video on series vs. parallel on the internet LOL.

Decided I'm going to make 2 types of adapters/pigtails for my panels. One will be a series adapter, the other a parallel. I have the plugs and wire for the one, have to spend about $20 to fabricate the other. Won't take long and neither adapter will be big, just some plugs and 4" of wire. Going to try one for a few camping trips and then the other, see if I can tell a difference. Home science experiment.