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Can't wrap my head around why there is so much loss when panels are so close to the same.

KnobCountry

KnobCountry

Leg puller. Zap avoider.
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Jan 28, 2024
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Behind the pond.
A 2 panels 20.2 vmp 5.2 imp
B 4 panels 19.23. Vmp 5.2 imp

2B+1A series
2B+1A series
Both strings parallel

Series / parallel calculators show I would lose 35% or more if I wire them 3s2p.

Why does less than a volt difference kill this much performance?
 
Well using the link in my signature the only large losses in the 30+% area was having a's in series and b's in series and paralleling them. That takes a huge hit not because the panels are off much in volts but because 2 panels is a BUNCH lower voltage in series vs 4 panels.
 
All panels wired in SERIES:

  • Max power output: 610.06W
  • Max power voltage (Vmp): 117.32V
  • Max power current (Imp): 5.2A
  • Loss: 0%

All panels wired in PARALLEL:

  • Max power output: 599.98W
  • Max power voltage (Vmp): 19.23V
  • Max power current (Imp): 31.2A
  • Loss: 1.65%

All identical panels wired in SERIES, then all series strings wired in PARALLEL:

  • Max power output: 420.16W
  • Max power voltage (Vmp): 40.4V
  • Max power current (Imp): 10.4A
  • Loss: 31.13%

All identical panels wired in PARALLEL, then all parallel strings wired in SERIES:

  • Max power output: 410.07W
  • Max power voltage (Vmp): 39.43V
  • Max power current (Imp): 10.4A
  • Loss: 32.78%
 
In series everything is at the same amps.

In parallel everything is at the same volts.

So if you take 2 panels and add them together you get around 40 volts and then with 4 panels in series you get 80volts.
But when you put the two series sets in parallel the volts are dropped to 40 volts of the 2 panel set. So 40 volts disappears. Thus the huge loss.
 
I'm putting 2 of one type B and 1 of A in series.

Then another series of 2 B and 1 A

This means the volts should be approx 58 on each series with 5 amps per series and then those series wired parallel for 58v 10 amps.

I feel like the calculators are leaving out that scenario?

19.23+19.23+20. 2=57.69 series 1 at 5 amps

19.23+19.23+20.2=57.69 series 2 at 5 amps

Parallel 57.69 10 amps
 
Last edited:
I agree, looks like it should do well 3s2p.
Although if their performance diverges in poor or off-angle light, that could hurt the heterogenous series strings.

Calculators, you say?
Bad algorithms, I would guess.

Those who can, do.
Those who can't, simulate.

Try all combos, if your MPPT and battery allow, and see what you get.
 
KnobCountry said:
I'm putting 2 of one type B and 1 of A in series.

Then another series of 2 B and 1 A

This means the volts should be approx 58 on each series with 5 amps per series and then those series wired parallel for 58v 10 amps.

I feel like the calculators are leaving out that scenario?

19.23+19.23+20. 2=57.69 series 1 at 5 amps

19.23+19.23+20.2=57.69 series 2 at 5 amps

Parallel 57.69 10 amps
Click to expand...
What you laid out makes perfect sense and should work fine. I'm telling you why the calculators are showing the huge loss. They are not combining the way you are wanting to combine them.
 
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