Go to the Northern Arizona Wind & Sun - Online Solar Store

Announcement

Collapse
No announcement yet.

Temperature Coefficients

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Temperature Coefficients

    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?

  • #2

    Re: Temperature Coefficients

    Re: Temperature Coefficients

    As far as I know--These 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 %/oC
    Vmp -0.52 -0.51 %/oC
    Imp 0.064 0.065 %/oC ["fix" value--- 0.006x is probably a data sheet typo. -Bill B.]
    Voc -0.36 -0.36 %/oC
    Isc 0.061 0.060 %/oC
    Operating Temp -40 to +90 oC
    The above numbers are in percent--So 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 watts--The 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
    Last edited by BB.; April 11th, 2012, 14:18. Reason: Imp 0.0064 0.0065 %/oC is most likely wrong--one too many zeros after decimal point
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

    Comment


    • #3

      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

      Comment


      • #4

        Re: Temperature Coefficients

        Re: Temperature Coefficients

        Originally posted by BB. View Post
        As far as I know--These 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 percent--So 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 watts--The 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
        I am finding that most are close like you suggest. I've noticed these values make a big difference when sizing wiring.

        Comment


        • #5

          Re: Temperature Coefficients

          Re: Temperature Coefficients

          The PV panels I'm concerned about are the Phono Solar PS230P-20/U.

          Comment


          • #6

            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 temperature--and 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). So--there 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 listed--which 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 useful--But 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 1-2 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 Vmp-hot and Voc-cold... Vmp hot depresses Vmp voltage and can stop a charger from full charging current or prevent a GT inverter from starting/running. Hi Voc-cold can damage switching electronics.

            -Bill
            Last 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.

            Comment


            • #7

              Re: Temperature Coefficients

              Re: Temperature Coefficients

              Originally posted by Etebari View Post
              I am finding that most are close like you suggest. I've noticed these values make a big difference when sizing wiring.
              Why? Wire sizing is based on current, and the variance in current from a PV module due to changes in temperature is very small.
              Last edited by ggunn; April 11th, 2012, 9:05.

              Comment


              • #8

                Re: Temperature Coefficients

                Re: Temperature Coefficients

                Thermal Characteristics Phono Solar PS230P-20/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.

                Comment


                • #9

                  Re: Temperature Coefficients

                  Re: Temperature Coefficients

                  Pmax = -0.46 %/C
                  Vmp = -0.52 %/C
                  Imp = 0.0061 %/C

                  This data doesn't make much sense. Imp temp coefficient is virtually zero. Therefore the temp coeff of Pmax should equal Vmp.

                  Comment


                  • #10

                    Re: Temperature Coefficients

                    Re: Temperature Coefficients

                    Thank you CalBiker--I agree--Imp 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.

                    -Bill
                    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

                    Comment


                    • #11

                      Re: Temperature Coefficients

                      Re: Temperature Coefficients

                      Originally posted by BB. View Post
                      Thank you CalBiker--I agree--Imp should be closer to ~0.061 %/C (I think that there is an extra zero after the decimal point).

                      -Bill
                      That looks lots better. If we want to be exact,

                      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

                      Comment


                      • #12

                        Re: Temperature Coefficients

                        Re: Temperature Coefficients

                        Thank you Cal!

                        Cool-We have a new poster that can take over writing some of the equation based answers/estimates I give--They even have a better chance of being correct too.

                        -Bill
                        20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

                        Comment


                        • #13

                          Re: Temperature Coefficients

                          Re: Temperature Coefficients

                          Thanks 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

                          Cal

                          Comment


                          • #14

                            Re: Temperature Coefficients

                            Re: Temperature Coefficients

                            Originally posted by calbiker View Post
                            Thanks 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

                            Cal
                            Well everybody makes mistakes. That's why we keep an eye on each other.
                            1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                            Ohm's Law: Amps = Volts / Ohms
                            Power Formula: Watts = Volts * Amps

                            Comment


                            • #15

                              Re: Temperature Coefficients

                              Re: Temperature Coefficients

                              Name:  5423bdef06650e9baa333cb2da51e2ef.jpg
Views: 1
Size:  182.8 KBName:  3176d20cef388c5ae972732c0b484b4c.jpg
Views: 1
Size:  122.5 KB

                              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.

                              Comment

                              Working...
                              X