Solar Panel Wiring Configurations - 2p2s vs. 2s3p vs. 4s

[barbtalon]

I've been going through some different panel configurations for my vanbuild. See the attached drawings of configs 1, 2, & 3.

Config 1 - All four panels in series. Produces 112 V, 5.32 A into the charge controller. 0.12% voltage drop.

Config 2 - Panels 3 & 4 in series, then 1 + 2 + 3/4 in parallel. Produces 37.2 V, 16 A into the charge controller. 1.12% voltage drop.

Config 3 - Panels 1&2 in parallel, panels 3&4 in parallel, then 1/2 + 3/4 in series. Produces 56.2 V, 10.6 A into the charge controller. 0.5% voltage drop.


This is a system I've already built, but am upgrading/redesigning. I'm getting a new charge controller (current one is undersized), and already have 10AWG wire in place (voltage drop calculations made using 10AWG wire). I already own panels 1 and 2, and am looking at purchasing 3 and 4 (all Richsolar panels). The charge controller feeds a LiFePO4 24V bank.


My thoughts on the configs:
Config 1 Seems like the worst to me. A monster 112 V into the charge controller is going to be inefficient. The only advantage is a low voltage drop.
Config 2 seems okay, but the highest current of the three configs produces the highest voltage drop of the three at 1.12%. This isn't a deal breaker, but I still would like to be as efficient as possible.

Config 3 seems like the best choice to me. 56 V wouldn't be too high for a controller, and 0.5% voltage drop is just fine. I've never seen someone make a setup like this where it's parallel first and then series; as far as hybrid configurations, I've only ever seen panels in series, and then parallel.

Will Config 3 work and is it my best bet here? Anyone have a charge controller to recommend? I have the Epever Tracer 1215BN, but it caps out at 10A max output.

 

[Rednecktek]

With a 24v system the 2s2p is going to be your best bet, so Config 4.

You'll have to put 2 in series to get enough voltage to charge a 24v battery. Putting those series panels in parallel will keep your VoC below limits. You'll need at least a 20a SCC to utilize those panels but a 40 buys you expandibility. If 1 panel gets shaded the other string still plugs along just fine.

Config 1 requires a really large SCC to avoid frying due to voltage and is easily nerfed by a little shade on a single panel.

Config 2 is about the worst possible option as everything will be nerfed down to the lowest voltage in the set and the lowest voltage.

Config 3 is close but runs the same shading issues as Config 1.

 

[Rocketman]

Go with 2s2p! Put the two in series first, then put the two super panels in parallel.

 

[barbtalon]

Hmmm by 2s2p, do you mean putting 1&3 in series, 2&4 in series, and then paralleling those two sets? I didn't think of that.

Yes @Rednecktek you're right, didn't notice that voltage nerfing about config 2. Definitely kills it.

So config 3 is similar to a 2s2p, except there are shading issues? Can you elaborate on why the shading affects this config (and config 1) but not a 2s2p?

 

[Rednecktek]

Hmmm by 2s2p, do you mean putting 1&3 in series, 2&4 in series, and then paralleling those two sets? I didn't think of that.

Exactly! Or 1&2 and 3&4. Either way works.

Yes @Rednecktek you're right, didn't notice that voltage nerfing about config 2. Definitely kills it.

That would have made you cry when your system didn't charge.

So config 3 is similar to a 2s2p, except there are shading issues? Can you elaborate on why the shading affects this config (and config 1) but not a 2s2p?

So if you put 2 in parallel and 1 gets shaded then the other works normally. However because you need higher voltage to charge the 24v battery, if you shade a panel then you've got something similar to Config 2 where the high voltage string is nerfed by the single panel still seeing sun. At that point ALL of your panels are nerfed and the system can't produce enoigh voltage to charge.

If you put them in series then what you have is the equivalent of a single 200w panel (each string) in parallel with another 200w panel (the other string) so if one "panel" gets shaded, the "other panel" still works normally.

Does that make sense?

 

[barbtalon]

Yes that mostly makes sense, thanks! I've never thought about panel independence before.

But I'm confused how a 1&2 + 3&4 2s2p configuration would not be nerfed.
Putting 1&2 in series gives 75.2 V, 5.32A.
Putting 3&4 in series gives 37.2 V, 5.38 A. (since 3&4 are half the wattage of 1&2)

Putting those two strings in parallel gives you 10.7 A, but the voltage is capped at 37.2 due to the smaller panels. However with the 1&3 + 2&4 combo, that problem doesn't occur.

Am I seeing this wrong?

 

[Rednecktek]

Nope, I was under the impression all 4 panels were the same. Yes, you're right going 1&3 + 2&4.

 

[barbtalon]

Cool thanks, I appreciate the help!

 

[GooseF16]

Im doing something very similar so yes, 1/3 and 2/4. I have 3 x 200 25v panels, and 3 X 100 25v panels, so I will put the string of 100's in series for 75 Volts and 4 amps, and I will place the 200's in a string with 75v and 8 amps.. then I will parallel those strings together in a parallel array, for a total of 75 Volta and 12 amps.. and get close to 900 watts.. so you would build the same string idea.. when you combine its always the lowest of the string that drives it series adds voltage, parallel adds amperage, but when you do both, you need to try to match the voltage, and if you do, the amperages will add.. If you hook a 100 w in series with a 200 watt of the same voltage, the amperage is reduced to the lowest of the panels to pass.. my string is a 3S 2P with 3x100 and 3x200.. I could get one more panel up there but cannot come with a configuration that wont limit it and render the panel useless.. unless I can stuff 75v of panels.. up there.. so fun.. I have a book full of drawings figuring the array out on my 7x14 solar trailer.. enjoy..