Quite often manufacturers only place Isc, Voc and Pmp temperature coefficients in their specifications but fail to post Imp and Vmp coefficients. Is there a way to derive those values mathematically without contacting the manufacturer?
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Re: Temperature Coefficients
Re: Temperature Coefficients
As far as I knowThese are physical characteristics of the silicon material itself and not really related to the specific manufacturer. Here are some numbers I would use (from a large Kyocera panel):
Pmax 0.46 0.45 %/^{o}C
Vmp 0.52 0.51 %/^{o}C
Imp 0.064 0.065 %/^{o}C ["fix" value 0.006x is probably a data sheet typo. Bill B.]
Voc 0.36 0.36 %/^{o}C
Isc 0.061 0.060 %/^{o}C
Operating Temp 40 to +90 ^{o}C
BillLast edited by BB.; April 11th, 2012, 14:18. Reason: Imp 0.0064 0.0065 %/oC is most likely wrongone too many zeros after decimal point20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

Re: Temperature Coefficients
Re: Temperature Coefficients
basically you'd be guessing. can you tell us what pv you are trying to find out about as somebody here may already know? worst case is you'd need to contact the manufacturer and while you are in contact with them suggest to them to list more specs.NIEL
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Re: Temperature Coefficients
Re: Temperature Coefficients
Originally posted by BB. View PostAs far as I knowThese are physical characteristics of the silicon material itself and not really related to the specific manufacturer. Here are some numbers I would use (from a large Kyocera panel):
The above numbers are in percentSo you just use the specific Vmp/Imp/etc. of the panel you are calculating the temperature factors for... Notice that even for identical panels except one is 315 watts vs 320 wattsThe numbers are slightly different (0.46 vs 0.45 for Pmax). Just guessing but these are probably identical panels just sorted for rated output.
Bill
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Re: Temperature Coefficients
Re: Temperature Coefficients
Sometimes, certain values do not really matter too much... For example Imp/Isc  Current is not affected too much by temperatureand in any case, most people use heavier copper cable than required to carry the solar panel current because they want to keep losses low (in the 1%3% range). Sothere is not too much reason to worry about "safety factors" for current capacity (check the numbers for fusing/breakers/conduit fill/insulation rating/etc... But, usually you will be using 2x or more thicker cable to keep solar power losses low).
And for parallel solar panel strings (three or more identical panel strings in parallel)There is usually a Series Protection Fuse listedwhich is somewhere around 1.56x Isc (typically). But a lot of vendors seem to leave that requirement off their data sheets. That value (also missing from the Phono Solar data sheets) should be a requirement for the designer / inspector for a system sign off (one or two parallel strings, fusing is not needed or usefulBut numbers should still be there to confirm).
I have seen a few high voltage (Vmp~100 volts or so) thin film panels (Dupont?) that had Isc in the 12 amp range, but a series fuse of ~15 amps. For those panels you can probably put three or four panels in parallel without fusing.
The usual "killers" in a design is Vmphot and Voccold... Vmp hot depresses Vmp voltage and can stop a charger from full charging current or prevent a GT inverter from starting/running. Hi Voccold can damage switching electronics.
BillLast edited by BB.; April 11th, 2012, 8:09.20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.
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Re: Temperature Coefficients
Re: Temperature Coefficients
Originally posted by Etebari View PostI am finding that most are close like you suggest. I've noticed these values make a big difference when sizing wiring.Last edited by ggunn; April 11th, 2012, 9:05.
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Re: Temperature Coefficients
Re: Temperature Coefficients
Thermal Characteristics Phono Solar PS230P20/U
Operating temperature range 45 to 85 °C
Temperature coefficient Pmpp 0.51%/K
Temperature coefficient Voc 0.37%/K
Temperature coefficient Isc 0.03%/K
If the manufacturer does not provide all the coefficients it is best to design the system using Isc and Voc just to be safe.
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Re: Temperature Coefficients
Re: Temperature Coefficients
Thank you CalBikerI agreeImp should be closer to ~0.061 %/C (I think that there is an extra zero after the decimal point).
I am going to correct/adjust my previous post.
Bill20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.
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Re: Temperature Coefficients
Re: Temperature Coefficients
Originally posted by BB. View PostThank you CalBikerI agreeImp should be closer to ~0.061 %/C (I think that there is an extra zero after the decimal point).
Bill
given:
TC_Vmp = 0.52 %/C
TC_Pmax = 0.46 %/C
Then
TC_Imp = ((1  TC_P) / (1  TC_Vmp))  1
TC_Imp = 0.0603 %/C
Cal
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Re: Temperature Coefficients
Re: Temperature Coefficients
Thank you Cal!
CoolWe have a new poster that can take over writing some of the equation based answers/estimates I giveThey even have a better chance of being correct too.
Bill20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.
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Re: Temperature Coefficients
Re: Temperature Coefficients
Originally posted by calbiker View PostThanks Bill, but now looking at my equation, I see an error. Results are the same.
Should be:
TC_Imp = ((1 + TC_P) / (1 + TC_Vmp))  1
Cal1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps
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Re: Temperature Coefficients
Re: Temperature Coefficients
Looks like I'm getting close to the values I expected, thanks for the input. TC for Pmp, Voc and Isc are on the PV label. Somewhere I read that the value of TCPmp=TCVmp+TCImp. Can anyone verify this? There will be dual Xantrex Controllers in parallel. Still trying to make sense of all of this so I can speed up design of other systems for myself.
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