Did I screw up with these panels.. NOCT of 46

ywhic
ywhic Solar Expert Posts: 621 ✭✭
in Off Grid Solar & Battery Systems #1
I bought (and they shipped).

3 of the 145 w panels..

The spec sheet says

STC 145
VMP 18.7
IMP 7.75
ISC 8.37
VOC 22.3

STC: 1000 W/m2, cell temperature 25 °C, AM=1.5

nominal operating temperature (NOCT) 46°C ±2°C
Temperature Coefficients of Pm -0.48 %/°C
Temperature Coefficients of Voc -0.34 %/°C
Temperature Coefficients of Isc 0.045 %/°C

I tried the MorningStar string calc and it came up with Isufficent Array Voltage..

I think/hope there may be a typo on the spec sheet but I am not sure..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Did I screw up with these panels.. NOCT of 46

    I see nothing wrong with those panel specs.
    18.7 Vmp is sufficient for a 12 Volt system. Multiply by Imp 7.75 and you get 144.9 Watts.
    Normal Operating Cell Temp of 46C is 115F.

    Why would you even need to use a string calculator for a simple 12 or 24 Volt battery-based system?
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #3
    Re: Did I screw up with these panels.. NOCT of 46

    Was trying to see the max I can get into the controller.. I've played with it all week.. prior to today..

    I couldn't figure out how an 18v panel could only make 2 volts at normal temps.. LoL.. got scared..

    After I moved 1 number in the co-effiecent % I came up with 5 panels and 725 watts max.. and 6 would be over the controller..

    I'm Thinking its because of this NEC stuff in the book:

    To comply with the National Electric Code (NEC), the current rating of the
    controller for solar charging must be equal or greater than 125% of the solar
    array’s short circuit current output (Isc). Therefore, the maximum allowable
    solar array input to the TriStar controller for compliance with the NEC is:

    TS-45: 36 amps Isc
    TS-60: 48 amps Isc


    Do you think 6 panels * 7.75 VMP (46.5 amps) would be ok.. or should I stop at 5 panels & 725 watts (38.75 amps)??

    I recall a conversation about CLIPPING of amperage with you.. and reading the booklet says something like 10% overage is allowed before clipping occurs.. which would be 49.5 amps max..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Did I screw up with these panels.. NOCT of 46

    Well the "2" is the +/- degrees of operating temperature; nothing to do with Voltage.

    As I recall, you're using a PWM controller so the maximum current out is basically just the Imp from the panels in parallel.

    The NEC derating rule for charge controllers is, in my opinion, flawed. It is based on the notion that a controller is a "constant use device" because it will be "on" for more than 3 hours a day (we certainly hope so). But in the real world it will not run at its peak current all that time. Although it is possible to run a controller at peak for 3 hours it is highly unlikely that will happen and it is not standard practice: i.e. if you're doing that the system is designed wrong. My take is that the fellow who comes up with these rules doesn't understand enough about the actual operating circumstances of solar electric systems, especially not of the off-grid variety. Xantrex actually has a setting for the C series controllers to be used as load controllers: meaning they intend them to handle up to full current constantly. Some other controllers state that they are meant to operate without any derating for current.

    Your 6 * 7.75 Amps is only going to occur under full sun conditions when demands (battery charging and load draws) require it. At that point the TS 45 will simply clip that 1.5 Amps if it is even really available. Remember that the sun does not shine brightly every day.

    This is another issue I disagree with the NEC on.
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #5
    Re: Did I screw up with these panels.. NOCT of 46

    Thanks for the info..

    It didn't make sense at all that the panels wouldn't work.. that would be a major issue I would think by now with someone whom had prior bought these.

    Someone must have dropped a 0 out of the VOC co-efficient.. should read -0.034 %/°C
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #6
    Re: Did I screw up with these panels.. NOCT of 46

    Ok.. apparantly no matter what I put into the calculator anything over 5 (and 725 watts) puts me over the VOC limit of 125v.

    Parameters are -5 F to 115 F..

    Per Panel..

    Minimum Voc (average high temp.) 20.70 Volts *5 panels = 103.5
    Max. Operating Voc (record low temp.) 22.96 Volts *5 panels = 114.8
    Max. Voc (record low Temp., morning) 23.85 Volts *5 panels = 119.25
    Minimum Vmp (average high temp.) 17.10 Volts
    Maximum Vmp (record low temp.) 19.36 Volts

    Unless I am reading this wrong..???

    I'd like 6 panels and 870 watts.. but I want them all to work all the time..

    With the TS60 (PWM) it says I would take it to 1015 worth and 7 panels..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Did I screw up with these panels.. NOCT of 46

    Okay Al: stop.
    You do not put five or six panels in series on a PWM controller.
    With that type of controller the array Vmp has to be in line with the system Voltage: i.e. one of those panels for a 12 Volt system, two in series for a 24 Volt system. No more. If you put the array together with six panels in series you will throw away the power because the system can not make use of the higher Voltage array: only an MPPT type controller can do that.

    Otherwise I'm not surprised it went over: 22.3 Voc * 5 = 111.5 Volts, factor in the temp coefficient for -5F and you can easily exceed that 150 input limit.

    In any case, it does not apply to paralleled panels feeding a PWM type controller, okay?
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #8
    Re: Did I screw up with these panels.. NOCT of 46

    I didn't say series or paralled.. I did mean 5 in parallel (or 6 in parallel) though.. Sorry..

    Think I will stick with 5 in parallel (725w) and use some of the save $ and get my 2000W Xantrex inverter and be done..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Did I screw up with these panels.. NOCT of 46
    ywhic wrote: »
    I didn't say series or paralled.. I did mean 5 in parallel (or 6 in parallel) though.. Sorry..

    Think I will stick with 5 in parallel (725w) and use some of the save $ and get my 2000W Xantrex inverter and be done..

    See, the string calculator is for putting panels in series; the Voltage goes up, the current stays the same. In parallel it's the other way 'round.
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #10
    Re: Did I screw up with these panels.. NOCT of 46

    It said 1 * 1 series *5 in parallel for the max for the controller using there calculator.. must be going by AMP's then for the IMP over the max of 45 at 46.5 then, or the ISC Amps coming in at 50.22 thats throwing the 6th panel out..

    I'll toss it in the breeze in the AM and figure 5 or 6 panels then.. 6 may be better because if 1 gets broke when I ship the mess to TX I will be out-of-luck..

    Again sorry for the confusion in the conversation..
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #11
    Re: Did I screw up with these panels.. NOCT of 46

    I emailed DM this morning.. and David (owner) got back to me.. yes it was a typo... will be revising the sheet soon..

    All is well. :D
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #12
    Re: Did I screw up with these panels.. NOCT of 46
    Cariboocoot wrote: »
    See, the string calculator is for putting panels in series; the Voltage goes up, the current stays the same. In parallel it's the other way 'round.

    Ok.. I've decided to probably get panel #6 (145w) when the shipment comes in.. and max out at 870 watts of PV..

    What I figured out with the silly Morningstar Calc is its based on straight up IMP number.. If I put in my true IMP of 8.05 (from the panel back) it tells me 5 panels in PARALLEL is good but 6 in PARALLEL is over.. If I drop the IMP number to 7.5, it tells me 5 and 6 panels is good to go...

    6 panels * 7.5 is exactly 45 amps.. (the rating for the TS-45).. the ISC numbers still set at the correct 8.95 didn't affect anything..

    Even though the panels are rated for IMP of 8.05 each I don't think it would really ever reach it, would it???
    (which would put me at 48.3 AMPS..).. again you mentioned the PWM adjusts VOLTS & AMPS as needed from the PV array based on load 'draw' to get the batteries back to that magic 14.4 absorb voltage.

    And again the clipping should occur or after the 10% allowance they mention in the manual.. (which would be 49.5 amps).

    I'd like your take on all this Cariboocoot..

    Granted with panel #6 I could then OPT to do a 24V battery bank and system.. (2 modules in series * 3 in parallel) and that would leave me additional wiggle room to grow..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Did I screw up with these panels.. NOCT of 46

    Al, it's all in the math.

    The Imp rating is what matters for paralleling in this instance. Five * 8.05 is 40.25 Amps, under the MS 45's max so they say "okay". Six times is 48.30 Amps which is over the max so it says "no go". Lower the Imp rating and you lower the totals so they come in under the wire.

    What's worse, if you were to follow the NEC regs on derating controllers it would really be a problem (their idea of the limit is 36 Amps - foolishness).

    But you are quite right: MS also says you can go 10% over, which is 49.5 Amps. Also, panels will only hit their max under conditions of maximum insolation and maximum draw (low battery and/or other load demands). For most of the time they won't be near maximum power (this is one of the reasons I disagree with the NEC derating).

    A PWM controller doesn't adjust Volts or Amps: it switches the panels on and off from the battery according to the Voltage it detects in order to maintain that set point (depending on the stage of charging). For Bulk it is 'ON'; all current available from the panels goes to the battery to maximize charging. When the Voltage hits the Absorb set point it starts to pulse; switching on and off as needed to maintain that Voltage for the specified time (this includes compensating for any load draws which would try to pull the Voltage lower, and might succeed). Then it drops to the Float level and does the same; switching on and off to keep the Voltage at the set point against the demands of the system.
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #14
    Re: Did I screw up with these panels.. NOCT of 46

    Actually its better than 10%.. just re-read it..

    From the TS-45 and TS-60 (PWM) manual..

    Solar overloads up to 130% of rated current will be tapered down instead of
    disconnecting the solar. Over-temperature conditions will also taper the solar
    input to lower levels to avoid a disconnect.

    Looks like 58.5 Amps max which would be why they say a 60 amp fuse/breaker before the controller..

    Either way I think I'll be ok..
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