MisterSandals
Participation Medalist
Exactly! The amps are different so their wire requirements are different.
If you have run lengths, we can figure your wire gauge requirements easily.
Solar panel combination..
- Thread starter GP28
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If you have run lengths, we can figure your wire gauge requirements easily.
There are 2 sides to your SolarChargeController that are calculated separately for wire size, max voltage and amps.
The solar panel side in Series and or Parallel connection of max Open Circuit Voltage(Voc) and Short Circuit Current(Isc):
amps limited by whatever Charge Controller you use.
SCC
The battery side could be 12 volt or 24 volts.
A 12.8 volt nominal battery is called 12 volts for convenience and the same for the panels labeled 12 volts.
Maximum Power Voltage(Vmp): 20.4V x Short Circuit Current(Isc): 10.2A
= 208 watts
Typical specs for a 200 watt panel:
Specifications RICH SOLAR 200 watt monocrystalline solar panel
- Maximum Power(Pmax): 200W
- Maximum Power Voltage(Vmp): 20.4V
- Maximum Power Current(Imp): 9.80A
- Open Circuit Voltage(Voc): 24.3V
- Short Circuit Current(Isc): 10.2A
- Maximum System Voltage(Vmax): 1000VDC
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You too damn fast. :D
I realized mistake and edited it.
@MisterSandals I wrote in post #14 in this thread regarding the diode selection. Of course, you can also just get diodes for this purpose already with an MC4 connector, like this one: https://thargo.com/product/mc4-blocking-diode-adapter-rated-20a/
An abbreviated answer of "Vmp @ Imp" is Greek to anyone new to solar.
I still have trouble remembering which one means what. lol
V = voltage I = current
mp = maximum power
sc = short circuit
Don't memorize. Understand.
mp = maximum power
sc = short circuit
Don't memorize. Understand.
So I checked my paperwork on my panels.
200W = VMP 21.0 ……………….. 210W = VMP 22.4
IMP 9.5 ………………… IMP 9.3
ISC 9.9 ………………... ISC 9.85
AVERAGE VMP = 21.7 ……….. WITH PANELS COMBINED VALUES
AVERAGE IMP = 9.4
AVERAGE ISC = 9.9
PARALLEL = ISC ( 9.9 x 2) = 19.8 AMPS @ 21.7 VMP
SERIES = VMP (21.7x2)= 43.4 VOLTS @ 9.9 AMPS
200W = VMP 21.0 ……………….. 210W = VMP 22.4
IMP 9.5 ………………… IMP 9.3
ISC 9.9 ………………... ISC 9.85
AVERAGE VMP = 21.7 ……….. WITH PANELS COMBINED VALUES
AVERAGE IMP = 9.4
AVERAGE ISC = 9.9
PARALLEL = ISC ( 9.9 x 2) = 19.8 AMPS @ 21.7 VMP
SERIES = VMP (21.7x2)= 43.4 VOLTS @ 9.9 AMPS
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Why are you making it so difficult on yourself
You have 200W on the input, so you'll have (minus some losses) 200W on the output. For a 12V (nominal) battery, 200W represents a current of 16A if your charge controller can deliver this and your panels produce it. Whether you put your panels in parallel or serial does not matter; in series you double the voltage at the same current and in parallel you double the current and keep the voltage. For any real power calculations on the solar side, you use Vmp and Imp (since this is what your MPPT controller will go for). The only reason you need Voc and Isc is to make sure your controller can handle these maxima.
You have 200W on the input, so you'll have (minus some losses) 200W on the output. For a 12V (nominal) battery, 200W represents a current of 16A if your charge controller can deliver this and your panels produce it. Whether you put your panels in parallel or serial does not matter; in series you double the voltage at the same current and in parallel you double the current and keep the voltage. For any real power calculations on the solar side, you use Vmp and Imp (since this is what your MPPT controller will go for). The only reason you need Voc and Isc is to make sure your controller can handle these maxima.
Got it, thank you so much for simplifying it.. That's what I originally thought, 2 panels at 200W = 400W total divided by either 12 or 24 volts to get basic need for design/layout options. 32 amps total parallel and 16 amps total series with noted total voltage differences used.
thank you and thank you all for the input....
thank you and thank you all for the input....
No problem. Always remember: https://diysolarforum.com/threads/repeat-after-me.5815/
VincentRapide
New Member
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- Jun 23, 2020
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> I realized mistake and edited it. [MBR]
No, you didn't. That matzoh ball still hanging out there.
> The only reason you need Voc and Isc is to make sure your controller can handle these maxima. [upno]
Lets pretend that the panels were finally connected electrically to the MPPT input terminals in the dead of a moonless night. Would that not negate the significance of Voc? That this might allow user to sneak three panels in series safely instead of a measly two? Assuming that it would be more efficient to feed 128.4v into an MPPT (with a max PV array Voc of 145vdc) than a mere 85.6v?
VR
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No, you didn't. That matzoh ball still hanging out there.
> The only reason you need Voc and Isc is to make sure your controller can handle these maxima. [upno]
Lets pretend that the panels were finally connected electrically to the MPPT input terminals in the dead of a moonless night. Would that not negate the significance of Voc? That this might allow user to sneak three panels in series safely instead of a measly two? Assuming that it would be more efficient to feed 128.4v into an MPPT (with a max PV array Voc of 145vdc) than a mere 85.6v?
VR
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No, Voc can occur on the terminals of the MPPT when connected and the MPPT controller is not drawing power from the panels because charging is disabled (battery full, or whatever reason). Then you need to keep in mind that Voc is specified at, I think, 25C. This can go quite a bit higher when it gets cold. So using your example and a typical temperature coefficient, the 42.8Voc can go to to e.g. 49V at -20C, meaning that you're now destroying your MPPT.
VincentRapide
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Oops, forgot about the V(cold boost). But I'm still curious if choosing instead Voc 44.5v panels for my next batch would prove to be more electrically efficient since now 3 are in series @133.5v (which is <145Vmax)? IOW feeding as much V into the MPPT as you can get away with would be somehow beneficial. TIA.
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The MPPT usually has an optimal input, but from personal experience, it doesn't matter too much. However, it's not that because an MPPT can handle 145V that it will actually operate at that voltage. Check the datasheet, usually the MPPT range sits 10V to 15V or so below the max voltage it can take. In addition, based on the batteries you have, this range is usually different as well. For example, from one of mine:
VincentRapide
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Ok, my [LV 5kva-48v] all-in-one specifies: PV array MPPT Voltage range: 60~115vdc. So for my Sunpower 250s there can only be 2 in series, never three. Thanks for clearing this up.
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