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packrat1969 avatar image

Series-Parallel vs Parallel Efficency

Currently I have (3) 100W panels wired in parallel that typically operate in the 17-19v range. During full sun they generate power in the 15-20A range. These are wired into an MPPT 100/50 unit that I purposely over-sized as I expect to grow the array incrementally over time. I have currently chosen the parallel configuration as it seems to have more immunity to partial shading, but I probably incur a penalty during full-sun conversion in terms of efficiency.

Aside from the extra power generated by adding a 4th 100 watt panel, would my full-sun power generation efficiency increase significantly by creating two pairs of series panels (for 34-38v) and then running these two series pairs in parallel? I'm sure the voltage increase would help with any cable losses I might have built into the system. Presently my smallest cable is the 10ga at the panels, but I do have nearly 40ft of 8ga and 6ga flexible copper cabling. The (3) 100W panels are set up as a portable/re-positionable ground array for replentishing (2) series-wired T105 6v deep-cycle golf-cart batteries on my RV. Basically I want to be able to recharge the 30% or so battery capacity that I consumed the previous overnight as fast as the batteries can handle (10% of 225Ah). Maybe someday I'll be able to afford to switch over to Lithium cells, but that will have to wait for now.

Honestly, setting up two separate two-panel arrays might seem like more work, but I think the lighter weight of two hinged panels vs the current three might make things easier to move around. It would also, of course, mean building more cabling and another panel frame mount.

Any relevant wisdom would be greatly appreciated.

packrat


BTW, what is it with the spell-checker on this site? I don't think I made up any new words today. It seems to red underline several legitimate words as well as much of the jargon I would expect used on this site....

Solar Panelparallelwiring
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3 Answers
Wildebus avatar image

I had 4 x 100W panels and I tried changing the setup from a Series-Parallel combination to a Series only to see if it improved the harvesting (less voltage drop, etc). I could not see any noticable difference in the harvesting in fact. I think you would likely need a very big array to see a real difference.

I have added a couple more panels and I am now running a 3-in-series + 3-in-series parallel setup.

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neoneddy avatar image

I do something similar. I'd love to do some A/B tests to get some real world numbers.


In ideal conditions, you should get more efficiency from higher voltages and lower amps. In partial shading, I believe it is different, parallel is better.

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packrat1969 avatar image

neoneddy,

I believe you are correct. Taking into account all the research I did before building my array, it appears that parallel configurations don't take as big as a performance hit if partial panel shading occurs. Most of the camping I do is under or very close to trees, so the parallel arrangement seemed to be a no-brainer. I have considered installing some DPDT switches so I can convert my 3-panel array from parallel to series and back (at will) to see if there are any efficiency gains when I can guarantee a day of full-sun, but I just haven't gotten around to seeking out the necessary parts.

The big drawback with parallel is the wire sizing for the current delivery. I managed to come across a couple of pairs of reasonably inexpensive large-gauge automotive jumper cables. I removed the big alligator clamps and installed the same Anderson connectors I put on my panel array. Plug and Play.


packrat

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