12 solar panels wiring

Dear guys,

I have 12 solar panels. Each panel Basic specs as below:-

Nominal output (Pmpp) 250

Voltage at Pmax (Vmpp) 30.5

Current at Pmax (Impp) 8.2

Open circuit voltage (Voc) 37.5

Short circuit current (Isc) 8.7


I am willing to buy an inverter with built in MPPT charge controller. Specs of the inverter as below:-

PV INPUT (DC)
Nominal DC Voltage / Maximum DC Voltage 360 VDC / 500 VDC
Start-up Voltage / Initial Feeding Voltage 116 VDC / 150 VDC
MPP Voltage Range 250 VDC ~ 450 VDC
Maximum Input Current 1 / 1 x 13 A

GRID OUTPUT (AC)
Nominal Output Voltage 208/220/230/240 VAC
Output Voltage Range 184 - 264.5 VAC
Nominal Output Current 13.1 A*

BATTERY & CHARGER
Nominal DC Voltage 48 VDC
Maximum Charging Current 25A


So here comes the question:-

I need to know how to wire the panels in series or parallel configuration or series/parallel combination so as to remain in the specifications of the inverter?

Please note I will have four batteries installed of 200AH each connected in series.

Any help would be highly appreciated :)

Comments

  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: 12 solar panels wiring

    If you mostly grid tied, I would connect them all in series, although you may be close to 500VDC limit if you're in a cold climate.

    If you're for battery charging, you may also consider two parallel strings of 6 panels because it is a lesser voltage drop between panels and batteries, so it might be slightly more efficient, but it is dangereous because you're getting to close to 150V limit, and your controller will shut down when it gets hot outside.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 12 solar panels wiring

    Is this the product you are looking at?

    Voltronic Infisolar 3kW GT Hybrid+MPPT Battery Charger

    • 2KW/3KW/5KW on-grid inverter with energy storage
    • Pure sine wave output
    • Microprocessor controlled to guarantee stable charging system
    • Multiple operations: Grid tie, Off grid, and grid-tie with backup
    • Built-in MPPT solar charger
    • LCD display panel for comprehensive information
    • Multiple communication
    • Green substitution for generators
    • User-adjustable battery charging current

    Interesting all-in-one product.

    It appears the specifications are for two different products (a smaller and a larger system). And 12 panels may not evenly power either product in its sweet spot.

    You are in Pakistan(?), so what are the minimum/maximum temperatures you see in your region (you can have some pretty wide temperature swings??)?... If it is very hot, too low of Vmp-array and the inverter will not start/run efficiently. If very cold, then Voc-cold can exceed 360 or 500 VDC and toast your system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring
    BB. wrote: »
    Is this the product you are looking at?

    Voltronic Infisolar 3kW GT Hybrid+MPPT Battery Charger




    Interesting all-in-one product.

    It appears the specifications are for two different products (a smaller and a larger system). And 12 panels may not evenly power either product in its sweet spot.

    You are in Pakistan(?), so what are the minimum/maximum temperatures you see in your region (you can have some pretty wide temperature swings??)?... If it is very hot, too low of Vmp-array and the inverter will not start/run efficiently. If very cold, then Voc-cold can exceed 360 or 500 VDC and toast your system.

    -Bill

    hey bill

    thanks for the reply.

    You caught me quite well :P

    It is Voltronics Infini 3 KW model.

    Regarding the temperature, it is mostly hot here. Average in summers is 40 Celsius. While in winters average shoud be around 15 Celsius. So its not a cold place actually. But the sunshine is quite much around the year.

    Please guide me whether I should go for this 3 KW model?
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 12 solar panels wiring

    OK, you have to "run the numbers" to figure out your Voc-cold-array and Vmp-hot-array (maximum array voltage to not damage controller, and minimum array voltage to start the controller--And, ideally, be in the "nominal" MPPT operating area).

    I cannot help you pick the controller--I know nothing about the company--And only what I quickly skimmed while looking at their website... You will have to read everything you can get your hands on to help you make your choice and ensure you are operating in the limits of the controller (many times, there are "hidden gems" in the manual that have tighter limits than the spec. sheet would suggest).

    The basic formula for figuring out the operating voltages. First, you need the temperature coefficients for your panels--Using a generic crystalline panel numbers:
    • NOCT 46 °C
    • TC Isc 0.004 %/K
    • TC Voc -0.30 %/K
    • TC Pmpp -0.45 %/K
    • Operating temperature -40°C to 85°C

    • Nominal output (Pmpp) 250
    • Voltage at Pmax (Vmpp) 30.5
    • Current at Pmax (Impp) 8.2
    • Open circuit voltage (Voc) 37.5
    • Short circuit current (Isc) 8.7

    Minimum temperature, maximum Voc-cold per panel (remember, this is real minimum temperature at sun up--You can have radiative cooling and if you get frost on the ground sometimes, then your minimum temperature is freezing or below):
    • Voc-panel = [email protected] (1 + Tc-oc(tcell-25C) = 37.5 Voc (1 + -0.003/K*(15C-25C)) = 38.625 volts Voc-cold-panel
    • # of panels Max = Max Controller Voltage / Max Panel Voltage = 500 VDC / 38.625 VDC = 12.9 = 12 panel maximum in series

    Maximum temperature, minimum starting Vmp-hot per panel. Remember here, you have ambient + temperature rise from solar radiation heating the panel--that can be upwards of 35C over ambient:
    • Vmp-panel = [email protected] (1 + Tc-oc(tcell-25C) = 30.5 Voc (1 + -0.003/K*(40Cambient+35Crise-25C)) = 25.5 volts Vmp-hot-panel
    • # of panels Max = Min Controller starting Voltage / Min Panel Voltage = 150 VDC / 25.5 VDC = 5.9 = 6 panel minimum in series

    The above numbers (6 minimum to 12 maximum) panels in series is right at the edge of the range... I am using generic numbers and your supplied information--You need to confirm my guesses and these numbers with your local supplier of the InfiniSolar inverter/charger to confirm that these meet their specifications (if you can).

    It appears that either two series strings of 6 or one series string of 12 will work... But if you get early morning frost on clear winter mornings, then your 15C minimum temperature may be too high of estimate and you need to recalculate.

    You may find that your "optimum" system with these panels is (based on 250 VDC to 450 VDC MPPT range) is:
    • 250 VDC Vmp range / 30.5 Vmp-hot per panel = 8.2 = 8-9 panels "optimum" minimum

    And 12 panels in series is too high...

    The maximum array of 3,200 watts:
    • 3,200 Watt / 250 Watts per panel = 12.8 panels maximum

    In the US, a MPPT type controller (GT inverter, or MPPT charge controller) can take a very large solar array because they will limit the GT/MPPT controller's output current automatically--So you can put more array on safely. In fact, for a typical 3kW MPPT device, I would have suggested:
    • 3,000 Watt rated output * 1/0.77 panel+controller derating = 3,896 Watt Array as being a "cost effective" maximum array

    You can go larger (need heavier wire and a series fuse or circuit breaker in case of short circuit--for safety)--But the controller should operate just fine and limits its output safely and reliably.

    I have seen several MPPT type devices out of Asia now that appear to have "hard limits" set on their input limits. I don't know if these are "true limits" or just somebody writing a generic specification.

    Is this making sense to you (lots of typing and math--I hope I did not make any mistakes)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring
    BB. wrote: »
    OK, you have to "run the numbers" to figure out your Voc-cold-array and Vmp-hot-array (maximum array voltage to not damage controller, and minimum array voltage to start the controller--And, ideally, be in the "nominal" MPPT operating area).

    I cannot help you pick the controller--I know nothing about the company--And only what I quickly skimmed while looking at their website... You will have to read everything you can get your hands on to help you make your choice and ensure you are operating in the limits of the controller (many times, there are "hidden gems" in the manual that have tighter limits than the spec. sheet would suggest).

    The basic formula for figuring out the operating voltages. First, you need the temperature coefficients for your panels--Using a generic crystalline panel numbers:
    • NOCT 46 °C
    • TC Isc 0.004 %/K
    • TC Voc -0.30 %/K
    • TC Pmpp -0.45 %/K
    • Operating temperature -40°C to 85°C

    • Nominal output (Pmpp) 250
    • Voltage at Pmax (Vmpp) 30.5
    • Current at Pmax (Impp) 8.2
    • Open circuit voltage (Voc) 37.5
    • Short circuit current (Isc) 8.7

    Minimum temperature, maximum Voc-cold per panel (remember, this is real minimum temperature at sun up--You can have radiative cooling and if you get frost on the ground sometimes, then your minimum temperature is freezing or below):
    • Voc-panel = [email protected] (1 + Tc-oc(tcell-25C) = 37.5 Voc (1 + -0.003/K*(15C-25C)) = 38.625 volts Voc-cold-panel
    • # of panels Max = Max Controller Voltage / Max Panel Voltage = 500 VDC / 38.625 VDC = 12.9 = 12 panel maximum in series

    Maximum temperature, minimum starting Vmp-hot per panel. Remember here, you have ambient + temperature rise from solar radiation heating the panel--that can be upwards of 35C over ambient:
    • Vmp-panel = [email protected] (1 + Tc-oc(tcell-25C) = 30.5 Voc (1 + -0.003/K*(40Cambient+35Crise-25C)) = 25.5 volts Vmp-hot-panel
    • # of panels Max = Min Controller starting Voltage / Min Panel Voltage = 150 VDC / 25.5 VDC = 5.9 = 6 panel minimum in series

    The above numbers (6 minimum to 12 maximum) panels in series is right at the edge of the range... I am using generic numbers and your supplied information--You need to confirm my guesses and these numbers with your local supplier of the InfiniSolar inverter/charger to confirm that these meet their specifications (if you can).

    It appears that either two series strings of 6 or one series string of 12 will work... But if you get early morning frost on clear winter mornings, then your 15C minimum temperature may be too high of estimate and you need to recalculate.

    You may find that your "optimum" system with these panels is (based on 250 VDC to 450 VDC MPPT range) is:
    • 250 VDC Vmp range / 30.5 Vmp-hot per panel = 8.2 = 8-9 panels "optimum" minimum

    And 12 panels in series is too high...

    The maximum array of 3,200 watts:
    • 3,200 Watt / 250 Watts per panel = 12.8 panels maximum

    In the US, a MPPT type controller (GT inverter, or MPPT charge controller) can take a very large solar array because they will limit the GT/MPPT controller's output current automatically--So you can put more array on safely. In fact, for a typical 3kW MPPT device, I would have suggested:
    • 3,000 Watt rated output * 1/0.77 panel+controller derating = 3,896 Watt Array as being a "cost effective" maximum array

    You can go larger (need heavier wire and a series fuse or circuit breaker in case of short circuit--for safety)--But the controller should operate just fine and limits its output safely and reliably.

    I have seen several MPPT type devices out of Asia now that appear to have "hard limits" set on their input limits. I don't know if these are "true limits" or just somebody writing a generic specification.

    Is this making sense to you (lots of typing and math--I hope I did not make any mistakes)

    -Bill

    Thanks Bill for such a detailed answer.

    I found you so helpful in my project and I learned alot.

    here goes the specs for the solar panels i bought.

    Nominal output (Pmpp) W 250
    Voltage at Pmax (Vmpp) V 30.5
    Current at Pmax (Impp) A 8.2
    Open circuit voltage (Voc) V 37.5
    Short circuit current (Isc) A 8.7
    Output tolerance % +3/-0
    No. of cells & connections pcs 60 in series
    Cell type - 6" Mono-crystalline silicon
    Module efficiency % 15.5
    Temperature coefficient of Pmpp %/K -0.44
    Temperature coefficient of Voc %/K -0.34
    Temperature coefficient of Isc %/K 0.052

    The lowest temperature we faced was 1 Celsius and that too in night time. Normally in winters it is around 15 Celsius.

    The highest temperature 48 Celsius. Normally it is 40 Celsius.


    sorry but I gave you avg temperatures but as you said we require highest/lowest for exact answer.

    Kindly calculate the optimum panels I should connect in series becuz the chinese inverter probably might not be fully upto the specifications mentioned.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 12 solar panels wiring
    inelastic wrote: »
    here goes the specs for the solar panels i bought.

    Nominal output (Pmpp) W 250
    Voltage at Pmax (Vmpp) V 30.5
    Current at Pmax (Impp) A 8.2
    Open circuit voltage (Voc) V 37.5
    Short circuit current (Isc) A 8.7
    Output tolerance % +3/-0
    No. of cells & connections pcs 60 in series
    Cell type - 6" Mono-crystalline silicon
    Module efficiency % 15.5
    Temperature coefficient of Pmpp %/K -0.44
    Temperature coefficient of Voc %/K -0.34
    Temperature coefficient of Isc %/K 0.052

    The lowest temperature we faced was 1 Celsius and that too in night time. Normally in winters it is around 15 Celsius.

    The highest temperature 48 Celsius. Normally it is 40 Celsius.

    I will run the numbers again for you... However, the poster/reader is responsible for confirming math/formulas/calculations. Most of us here are not in the solar business and can only offer our educated suggestions.

    Minimum temperature, maximum Voc-cold per panel (note that -0.34% = -0.0034 in formula below):
    • Voc-panel = [email protected] (1 + Tc-oc(tcell-25C) = 37.5 Voc (1 + -0.0034/K*(1C-25C)) = 40.56 volts Voc-cold-panel
    • # of panels Max = Max Controller Voltage / Max Panel Voltage = 500 VDC / 40.56 volts = 12.4 = 12 panel maximum in series
    • 12 panels * 40.56 volts @ 1C = 486.72 volts Voc-array-cold

    Still looks OK with 12 panels...


    Maximum temperature, minimum starting Vmp-hot per panel. Remember here, you have ambient + temperature rise from solar radiation heating the panel--that can be upwards of 35C over ambient:

    • Vmp-panel = [email protected] (1 + Tc-oc(tcell-25C) = 30.5 Voc (1 + -0.0034/K*(48Cambient+35Crise-25C)) = 24.4854 volts Vmp-hot-panel
    • # of panels Max = Min Controller starting Voltage / Min Panel Voltage = 150 VDC / 24.4854 VDC = 6.13 = 7 panel minimum in series
    • 6 panels * 24.4854 Vmp-hot = 147 volts
    • 7 panels * 24.4854 Vmp-hot = 196 volts

    The optimum minimum MPPT voltage is 250 VDC for your controller:
    • 250 volts min MPPT / 24.4854 Vmp-hot = 10.2 panels = 11 panels minimum

    And this is an "issue" with many MPPT type devices--You have a very "tight range" of ~10-12 panels where the array would meet the "nominal" specification for the controller.

    For any climates that have relatively large span between Summer and Winter temperatures, you need around a 2:1 range of solar array voltage to operate "in spec" (here 24.5 volt Vmp-hot to 40.56 volts Voc-cold).

    So, I believe you have 12 panels--The optimum range is probably ~11-12 panels in series. Assuming the Controller meets its specifications. If you are interested in experimenting--You could try two series strings of 6 panels each, then connected in parallel (series/parallel). And monitor the operation of your system. In theory, both should work with the 6x2 string, possibly, having a bit of trouble operating on very hot days, and possibly harvesting a bit less power too (operating below 250 VDC MPPT -- maximum power point tracking -- range).

    If you can get an answer from the supplier/factory--It would be interesting to hear there answer.

    Running at either end of the voltage range (6x2 or 12x1) will have "interesting issues" with the controller... I am not sure I have a favorite choice here. Obviously, I know nothing about the internals of this device.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring

    Guys thanks for all the information.

    The inverter specs show this
    MPP Voltage Range 250 VDC ~ 450 VDC
    Number of MPP Trackers / Maximum Input Current 1 / 1 x 13 A

    Is not this too less a charge controller to handle solar panels DC input of 3000 watts. I mean would this result in wastage's of electricity produced by panels?
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring

    Guys thank you for your effort to share information/knowledge.

    I have got the setup installed since 2 weeks, and its been working perfectly :)
    I have installed 12 panels in total.

    Normal temperature during the day time nowadays is 30^C in which the voltage shown on the multimeter/inverter-lcd is 330-350V.
    Now i am a bit concerned/worried about the coming of month of dec/jan/feb, in which day time temperatures reach till 2^C. Our lowest record temperature -1^C at night time.

    Now considering this temperature range, is it safe to use the 12 panels considering the specs of the inverter/controller as the inverter has built-in mppt charge controller.

    PV INPUT (DC)
    Nominal DC Voltage / Maximum DC Voltage 360 VDC / 500 VDC
    Start-up Voltage / Initial Feeding Voltage 116 VDC / 150 VDC
    MPP Voltage Range 250 VDC ~ 450 VDC
    Maximum Input Current 1 / 1 x 13 A
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 12 solar panels wiring

    Very happy to hear that the system is working well for you.

    From the math, the system seems find at ~0C ... If you have excess power in winter and are a bit nervous--You could cut back to 11 panels when you get a cold snap.

    You are dealing with "physics" so the panels should be predictable in how they behave. you could disconnect the array early one morning and measure the Voc-cold with good DC volt meter and see what it really displays.

    You don't have to do it at -1C record... You can do it at 4C or whatever, and make sure the scaling factors are correct (i.e., if 4C prediction and measured are almost the same, then 1C will be too (and you do still have a ~13 volt buffer below 500 VDC max).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring

    Thanks Bill :)

    Happy to see such an helpful person on this forum.

    Thats true i still have 13 volt buffer but does this mean exceeding the 450VDC MPPT range could result to burning of the charge controller?
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: 12 solar panels wiring

    It should not--It just means that the controller will no longer search for Pmp=Vmp*Imp -- So, your charge controller will not harvest the maximum amount of power when Varray is over 450 VDC.

    Does that mean a 12 panel array running cold will produce less charging current vs an 11 panel cold array? Not really sure. If it is easy for you to test (wire or switch to remove the last panel), it would be an interesting test. If you can set it up to be easy/reliable to change--You could always run 11 panels during winter and 12 panels they other 9 months.

    It is "close"--But many times electronic systems are designed to operate to their rated voltages/power/etc... Will the inverter/charger/controller last longer if you run it 30 volts less--I don't know, but it is possible. Is it worth the hassles of swapping the last panel in/out--Only you know that.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring
    NorthGuy wrote: »
    If you mostly grid tied, I would connect them all in series, although you may be close to 500VDC limit if you're in a cold climate.

    If you're for battery charging, you may also consider two parallel strings of 6 panels because it is a lesser voltage drop between panels and batteries, so it might be slightly more efficient, but it is dangereous because you're getting to close to 150V limit, and your controller will shut down when it gets hot outside.

    Thanks for the reply.

    Actually, I can't connect 2 strings in parallel because that would make ~18 amps from solar array whereas my MPPT charge controller max support is 13.1Amps.
  • inelasticinelastic Registered Users Posts: 11
    Re: 12 solar panels wiring
    BB. wrote: »
    It should not--It just means that the controller will no longer search for Pmp=Vmp*Imp -- So, your charge controller will not harvest the maximum amount of power when Varray is over 450 VDC.

    Does that mean a 12 panel array running cold will produce less charging current vs an 11 panel cold array? Not really sure. If it is easy for you to test (wire or switch to remove the last panel), it would be an interesting test. If you can set it up to be easy/reliable to change--You could always run 11 panels during winter and 12 panels they other 9 months.

    It is "close"--But many times electronic systems are designed to operate to their rated voltages/power/etc... Will the inverter/charger/controller last longer if you run it 30 volts less--I don't know, but it is possible. Is it worth the hassles of swapping the last panel in/out--Only you know that.

    -Bill

    I can take out the last panel easily but i think I should conduct some regular tests to know the max voltage achieved.

    After getting proper results, I should opt for taking 1 panel out, I Guess!
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