Array Sizing

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firefly
firefly Solar Expert Posts: 66 ✭✭
in General Solar Power Topics #1
Is there a simple way to determine what a MX60 can handle for putting together an array, be it 12, 24 or 48 volt?
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
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    Re: Array Sizing

    Sure 60 amps time the nomial voltage

    60 X 12 = 720 watts
    60 X 24 = 1440 Watts
    60 x 48 = 2880 Watts

    Then you need to figure the number of panels and parrallel strings and make sure the min/max allowed voltage is OK and doesn't exceed the above wattage
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Array Sizing

    But remember, you often only get 75 - 85% of the STC value of the panels, so for 48V, you could likely go to 3200W of PV safely. Some inspector may get a bug about it, because on a cold day, and the sun came out from behind a cloud you might go over spec a bit, but the MX60 is supposed to be tough.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Array Sizing

    by nec rules it is less so multiply those wattage figures by .80. there's also a modification for the mx60 to handle more current and i don't know if that mod is approved or not, but that would still need derated because of the nec rules even if that mod is approved.
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #5
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    Re: Array Sizing

    Sorry for not thanking everyone sooner, but had to put out some other fires. The process seems rather simple, but I know there must be more. I have two different types of panels, 4 Kyocera 12 volt 51 watt, optimum votage 16.9 and 2 Solar World 24 volt 165 watt, open circuit voltage VOC 44.0. The only ones hooked-up right now are the Kyocera and they are wired in series for 48 volts. By adding the 2 Solar World 24v 165 watt in series for 48, where will this leave me for the Maximum 141 VDC for the MX60. I really do not understand 12 volt panel, but 16.9v or 24 volt panel and 44 volt, nor the 141VDC or how to arrive at that number, when combining various panels. If in wiring in series the VOC or Optimum voltage doubles then I quest I am at 155.6V for this combination or NOT. Confused:confused:
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
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    Re: Array Sizing

    You would put the pair of solar worlds in series and then that gets parralled with the string of 4 Kyocera's

    The Solar world and KC's have different amperages and should not be put in series.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #7
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    Re: Array Sizing
    Is there a simple way to determine what a MX60 can handle for putting together an array, be it 12, 24 or 48 volt?
    Firefly,

    The “simple” answer is as follows:
    • For a system with a nominal 12 V battery, the MX60 is factory rated to handle a PV array rated at ~800 W STC
    • For a system with a nominal 24 V battery, the MX60 is factory rated to handle a PV array rated at ~1,600 W STC
    • For a system with a nominal 12 V battery, the MX60 is factory rated to handle a PV array rated at ~3,200 W STC
    The MX’ upper voltage limit is usually not an issue for systems with 12 V or 24 V battery systems. The PV array “sweet spot” STC voltage is between ~83 V and ~90 V. At 83 V, the array’s operational bulk/MPPT voltage will be high (>62 V) enough in the summer to comfortably reach the EQ voltage requirement for a flooded-cell battery bank. Below ~90 V, the array’s STC Voc (~112 V) won’t get too high in the Canadian winter (125% correction factor for -40 C; ~140 V) to shut down and/or damage the controller.

    Is this what you need?

    HTH,
    Jim / crewzer
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #8
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    Re: Array Sizing

    My intention was to have each on their own breaker at the Combiner box, the 4 KC's in series to one breaker and the 2 Solar World in series to their breaker. But I still don't understand how the 141VDC builds up. Doing it this way what would be my total VDC for the MX60, and would I be able to add another 2 Solar World 165's later this year? Is there a formula for figureing all this out?
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #9
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    Re: Array Sizing

    Being very new to this I am having a hard time getting my head around the equations, knowing what each different term actually means and how it relates to another.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #10
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    Re: Array Sizing

    Firefly,

    Don’t worry about being new and/or corn-fuzed. All of us on this site were once one, the other, or both. :roll:


    Your Solarworld 165 module’s Voc spec is 44.0 V. For two of ‘em wired in series, the string STC Voc will be 44.0 V x 2 = 88.0 V. Module voltage must be corrected for low ambient temperature. Assuming the winter morning low in your neck of the woods is ~-40 C (also -40 F), then the general temperature correction factor is 125%. 88.0 V x 125% = 110 V, which is well below the MX60’s 141 V operational limit. :cool:


    HTH,
    Jim / crewzer
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #11
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    Re: Array Sizing

    I know this is a very "dumb' question, but what makes up the 141 VDC that the MX is refering too?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #12
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    Re: Array Sizing

    Think of solar panels as batteries... Putting them in series adds voltage, putting them in parallel adds current.

    The issue with solar panels is that they are not "very stable" batteries. Roughly, from what I have seen, a solar panel's voltage can vary over temperature and loading conditions...

    For example when the panel is hot, the output voltage drops and you have to make sure that the minimum panel voltage will still support the maximum required battery voltage (at its coldest expected temperature--during equalization, for example) at the panels hottest temperature (full sun, no wind).

    And on the other side, when the solar panels are ice cold, and no load (batteries charged, no current flow, or other issues), the panels can output almost 2x Vmp (Voltage max power) for Voc (Voltage open circuit). And you need to make sure that it does not exceed the maximum voltage of your solar controller.

    It may be a bit confusing, but I played around with the Xantrex Grid Tie inverter sizing tool... You can put in different panels and temperatures--and it will give you min/max voltages.

    You also have to worry about about current (Isc = current short circuit an Imp = current maximum power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #13
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    Re: Array Sizing

    4 KC in series Vpmax= 4 * 16.9= 67.6 volts, Voc (voltage open circuit) would likely be around 21 volts for these panels and the actual Voc should be stamped on back of panels ~4 *21=84 volts Pmax when wired in series.

    The SolarMax Voc as you stated is 44 volts. Two in series would be 88 volts. You would parallel the two series strings with a Voc at 84-88 volts, well under an MX60 specs. I suspect with a 24 or 48 volt battery system, you will be anywhere near the MX60 max current rating with the panels you have. I hope this helps.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #14
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    Re: Array Sizing
    I know this is a very "dumb' question, but what makes up the 141 VDC that the MX is refering too?

    The MX60's absolute maximum input voltage is 150 VDC. Above that, internal components may/will be damaged. If the input voltage from the array exceeds ~141 V, the MX will enter a self-protection mode and disconnect the array. Once the array voltage falls below ~141 V, the MX will reconnect and return to normal operation.

    It's essential that a temperature correction factor appropriate for the array's location and ambient temperature conditions be applied when calculating maximum array voltage. This requirement applies to any brand controller, and, if you follow the NEC, it applies to voltage ratings for circuit breakers and/or fuses as well. Alternately, the module's Voc temperature coefficient can be used; see the module spec sheet.

    Here are the NEC 690-7 temperature correction factors:

    77 F to 50 F (25 C to 10 C): 106%
    49 F to 32 F (9 C to 0 C): 110%
    31 F to 14 F (-1 C to -10 C): 113%
    13 F to -4 F (-11 C to -20 C): 117%
    -5 F to -40 F (-21 C to -40 C): 125%

    Your Solarworld 165 module’s Voc spec is 44.0 V. For two of ‘em wired in series, the string STC Voc will be 44.0 V x 2 = 88.0 V. Module voltage must be corrected for low ambient temperature. Assuming the winter morning low in your neck of the woods (Ontario, Canada?) is ~-40 C (also -40 F), then the general temperature correction factor is 125%. 88.0 V x 125% = 110 V, which is well below the MX60’s 141 V operational limit.     :cool:

    HTH,
    Jim / crewzer
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #15
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    Re: Array Sizing

    First let me say a "BIG THANKS" to all. It will take me awhile to digest this, but I think I see a light at the end of the Panel. I will try to do some of my own calsulations, then post for comment. Again many thanks.
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  • firefly
    firefly Solar Expert Posts: 66 ✭✭
    #16
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    Re: Array Sizing

    Back again with another question, with my 4 51 watt KC'S in series with a VOC of 86.8 and my 2 165 watt SW's in series with a VOC of 86.6, can I just run them separately to my combiner box and have each string oin a separate 15 amp breaker or due I have to parallel them first, and then run to a single breaker?
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #17
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    Re: Array Sizing

    Best would single breaker per string them combine, make trouble shooting easier
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