Adding to current solar system

phaeton10phaeton10 Registered Users Posts: 7

This is what I have currently and what I am adding.  My questions is my purposed wiring heavy enough and if not what would be the correct size to handle my addition.

Current panels: 

3- Kyocera KD 135GX  12 volt panels 

VMPP 17.7V

IMPP 7.63A

ISC 8.37A

 Adding these panels

 3- Kyocera KD 140SX  12 volt panels

 VMPP 17.7V

IMPP 7.91

ISC 8.68

 I will mount these in 2 strings, 3 current panels on one side of motorhome and the 3  new panels on the other side.  I will be using a combiner box on the roof.  The reason for mounting on each side is to help with shading, My three AC units blocks some sun where we boondock, either in the morning or the evening.

 String each set with #10 wire to the combiner box and from combiner box to controller using existing # 6 wire approximately 18 feet.  (Hopefully this #6 is large enough).

From controller to (6) 6V battery bank is 18 feet again using #6 wire. 

The controller is an Outback Flexmax 80. 

My question is,  which would be the best way to wire the panels in series or parallel?

 

Comments

  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Welcome to the forum,

    I am not sure that I understand exactly how your existing panels are configured... You refer to them as a string, which to me means that they are in series and the string voltage is 3 X 17.7 = 53.1 volts.  Is that correct?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • phaeton10phaeton10 Registered Users Posts: 7
    I believe when the original panels were mounted they were mounted as parallel.  I only had a 25 amp controller with that set up.  I want to run them in series if possible. 
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    phaeton10 said:
    I believe when the original panels were mounted they were mounted as parallel.  I only had a 25 amp controller with that set up.  I want to run them in series if possible. 
    What controller do you plan to use after you add the 3 new panels? 

    Why do you want panels in series?  There may be some advantages to keeping a parallel configuration, especially since shading is an issue. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • phaeton10phaeton10 Registered Users Posts: 7
    vtmaps said:
    phaeton10 said:
    I believe when the original panels were mounted they were mounted as parallel.  I only had a 25 amp controller with that set up.  I want to run them in series if possible. 
    What controller do you plan to use after you add the 3 new panels? 

    Why do you want panels in series?  There may be some advantages to keeping a parallel configuration, especially since shading is an issue. 

    --vtMaps
    Outback Flexmax 80.  I am a newbee and when I bought the panels and controller he sales guy at Northern Arizona  told me the #6 cabling along as going in series would be sufficient for the 6 panels.
  • phaeton10phaeton10 Registered Users Posts: 7

    I am being told by others the problem is with the cable size #6  from the controller to the batter bank being 18 feet is not heavy enough, that it should be #1 or #2 AWG


  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    phaeton10 said:
    Outback Flexmax 80.  I am a newbee and when I bought the panels and controller he sales guy at Northern Arizona  told me the #6 cabling along as going in series would be sufficient for the 6 panels.
    I'm not sure what you are trying to say...
    phaeton10 said:

    I am being told by others the problem is with the cable size #6  from the controller to the battery bank being 18 feet is not heavy enough, that it should be #1 or #2 AWG


    I am not sure we are speaking the same language... which cable is 18 ft?  If it is from the controller to the battery, then yes, it needs to be heavier.  And how you configure the panels (series,parallel) is irrelevant. 

    If you are referring to the cable from the combiner to the controller, then it does matter how you have the panels configured.

    You have cables from the panels to the combiner.  These are probably 10 gauge and are part of the panel.  These cables run to a combiner.  From the combiner there is a cable that carries the combined current to the controller.  What is the length of the combiner-controller cable?

    A group of panels when wired in series is called a string.  The voltage of the string is the sum of the individual panel voltages.  A string may consist of just one panel.

    The strings of panels are combined in the combiner box.  That means the strings are parallel to each other.  Each string should have a circuit breaker in the combiner box.  The circuit breakers are desirable with any number of strings, and are required if there are more than 2 strings.

    In your system, with 6 panels, there are several ways to configure the panels:

    string length = 1  This means your panels are all in parallel.  You have 6 strings and 6 circuit breakers in the combiner.  The Vmp of the strings is 17.7 volts.

    string length = 2  This means you have 3 strings and 3 circuit breakers in the combiner, each string being 2 panels in series.  The Vmp of the strings is 35.4 volts.

    string length = 3  This means you have 2 strings and 2 circuit breakers in the combiner, each string being 3 panels in series.  The Vmp of the strings is 53.1 volts.

    string length = 6  This means you have 1 string and 1 circuit breaker.  The Vmp of the string is 106.2 volts.

    There are advantages and disadvantages to each of these configurations.  Shading is just one of many considerations.  Since you do have shading issues you should try to have as short a string length as possible.  This is because shading of one panel will reduce the output of the entire string, not just the shaded panel.  With a string length of 1, you have 6 parallel panels.  If one gets knocked out by shade, the other five panels can still produce.  If you have (for example) 3 strings, and 1 panel is shaded, you lose the output of 2 panels (the shaded panel and the unshaded panel in the same string).

    On the other hand, there may be some downsides to a string length of 1.  In particular, there is the issue of voltage drop.

    Tell us more about the distances involved between the panels and the combiner, the combiner and the controller, and the controller and the battery.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • phaeton10phaeton10 Registered Users Posts: 7
    edited September 2015 #8

    From my panel to the combiner box is 5 feet (combiner box mounted on the roof)

    18 feet (#6) from combiner box to controller.

    18 feet (#6) from a Flowmax 80 to batter bank.

  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    phaeton10 said:

    From my panel to the combiner box is 5 feet (combiner box mounted on the roof)

    18 feet (#6) from combiner box to controller.

    18 feet (#6) from a Flowmax 80 to batter bank.

    OK, now we have some numbers to work with.   The first problem is the distance between the controller and the battery.  With 825 watts of panel, a 12 volt battery, and 18 ft (one way) of #6 copper, you are looking at almost 4% voltage drop.  That's too much.   The two most common solutions for this problem are to have the controller very close to the battery, and to use a higher battery voltage.   The other solution is to use heavier cable.  If you use #2 cable you can have a voltage drop of 1.5%.  If you use #0 cable you will have a 0.9% voltage drop.

    Now, onto the second problem.  This is the cable between the combiner and the controller.  Here you have some choices.  Your controller is an MPPT type controller which means that it can efficiently step down higher voltages to battery voltage.  The higher your string voltage, the thinner your combiner-controller cable can be.  For example, if you configure your array as 3 strings, with a string length of 2, then the voltage drop with #6 cable is less than 1%.

    As I mentioned previously, there are other considerations in your choice of string length.  The shading problem is less of a problem with a shorter string length, but with a string length of 1, you need some very heavy cable.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • phaeton10phaeton10 Registered Users Posts: 7

    vtMaps, now this is the answer I have been looking for.  I relooked at my real estate on top and I will  be able to place the 3 new panels where shading should not be a problem.

    Unfortunately I can not relocate the controller due to space.

    I plan on running just 2 strings, 3 panels each and if I read correctly if I run these in series, each string will be 36 volts to the combiner box and the #6 from there to the controller will be fine.  Then I will bump up the cable from the controller to the batteries to a # 2.

    vtMaps, I want to thank you for your help.

  • phaeton10phaeton10 Registered Users Posts: 7

    One last question,  what size fuses should I use for this setup?


  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    If you have less than three parallel strings of solar panels, you do not need fuses/breakers for the solar panel string.

    For the charge controller to battery bank, you need wiring+fusing that will support:
    • 825 Watt solar array * 1.25 solar energy variation * 1.25 NEC derating * 1/12 volt battery bank = 107 Amp rated breaker+Wiring
    If you are using an FM 80, the maximum output current from the MPPT type solar charge controller is 100 Amps, so:
    • 80 amp controller output * 1.25 NEC wiring+breaker derating = 100 Amp rated wiring+breaker minimum
    In this case, 100 Amp rated wiring and breaker minimum should be fine.

    Check the manual for the FM 80--They are generally pretty detailed about installation requirements.

    And while you can use fuses--You might look at using circuit breakers instead. Breakers are not much more (and are sometimes cheaper) than fuses, and it can be nice to have an "on/off" switch to service the various pieces of equipment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    phaeton10 said:

    One last question,  what size fuses should I use for this setup?

    Your panels have a 'series fuse rating'.  Probably about 15 amps.  That is the size to use in the combiner box for each string of panels.

    The combiner-controller cable should have a circuit breaker at the controller end which serves as a PV disconnect switch.  Since that is #6 cable, you can use up to a 60 amp breaker, although your PV current will be only about 16 amps.

    One of the most important fuses (or circuit breakers) is between the battery and the controller.  If you are using #0 cable, you could use up to a 150 amp breaker, but a 100 amp breaker would be safer. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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