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STC vs NOCT

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  • STC vs NOCT

    When sizing a system for the RV should I really be using the NOCT numbers for the output?

    I am looking at the[SIZE=12px] LG300S1C-A5 High Efficiency Mono X with Parallel connections

    2 panels using NOCT numbers= Min Tmp 36.6 A, Max Tmp 29.3 A
    2 panels using STC numbers= Min Tmp 50.6 A, Max Tmp 38.1 A

    3 panels using NOCT numbers= Min Tmp 54.9 A, Max Tmp 43.9 A
    3 panels using STC numbers= Min Tmp 70 A, Max Tmp 57.1 A

    The panels will be very close to Flat Mounted. maybe 3-5 degree pitch
    I am thinking even NOCT numbers might be much higher than flat mounted panels will achieve.

    As I live in the southwest at about 32 degree North latitude I might need to have the 3rd panel on a set of separate circuit breakers so I can turn it off during the summer months while at that latitude.

    What are others experiencing for the output of RV mounted panels?

    I am assuming my Victron 100/50 would put out a lot more heat if the power tried to go past 50 amp.

    -Bill






    Last edited by Bigbillsd; 06-01-2018, 11:00 AM.

  • #2
    Neither. With panels pointing straight up disqualifies manufactures optimum rating. For an RV you size to achieve maximum charge rate. Even that will not likely be enough.
    MSEE, PE

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    • #3
      So I should size them to produce 50 A? Which is about 600 watts tilted toward the sun. I wonder how many watts if they are flat on my RV roof? I was kind of hoping I wasn't the trail blazer and someone else may have already hacked their way thru the undergrowth.. -Bill

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      • #4
        First the numbers you have posted are complete nonsense.

        2 panels using NOCT numbers= Min Tmp 36.6 A, Max Tmp 29.3 A
        2 panels using STC numbers= Min Tmp 50.6 A, Max Tmp 38.1 A
        Neither myself or anyone has any clue what this garbage is. I know it is not Temperature, Amps, Volts, or Watts. Cannot tell you how many watts it takes to do anything because you have not specified anything other than garbage.
        MSEE, PE

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        • #5
          Use any of the solar PV est sites, and use flat, as your mounting angle. to get a production est.
          Powerfab top of pole PV mount (2) | 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

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

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          • #6
            Originally posted by Sunking View Post
            First the numbers you have posted are complete nonsense. Neither myself or anyone has any clue what this garbage is. I know it is not Temperature, Amps, Volts, or Watts. Cannot tell you how many watts it takes to do anything because you have not specified anything other than garbage.
            I guess we need some pretty thick skin to ask questions here.

            Its panel temperature vs the possible amps output from the controller to the batteries. I had thought 0 and 70 Celsius were some sort of standards as I see those same temps in a couple different panel calculators I've used.
            Min Tmp is 0 degrees centigrade and max is 70 degrees centigrade as there is a significant difference in the power produced based on the temperature of the black panels out in the sun. I was thinking that STC vs NOCT kind of reflected higher temps and a less than optimum angle toward the sun.

            Anyway, I am just trying to figure out how many panels to put on the roof of the RV. I'm trying not to buy too few and then have an issue getting more of the same panels, and I'm not wealthy enough to buy a bunch just in case.

            My goal is to replace/charge about 200 Ah of daily use from my 4 6volt CR-260 Crown FLA batteries configured for 12v when dry camping. From what I have gathered on this forum I may be close to impossible to get a full charge from solar (I hadn't heard that before) So I will probably need to use my generator early in the mornings for some period to bulk charge them and hope my flat mounted panels put out enough power to get the other 20% put back into the batteries while there is sunlight.

            I prefer to minimize the quiet diesel generator use as much as I can for as reasonable a cost as I can. I calculated that I will use about $600 in diesel fuel this year to run the genny to charge the batteries. If I can cut that down by 2/3 I could save about $400 a year and make the solar pay for itself in a few years. Currently I have $650 cash invested in the portable suitcase panels including the 100/50 amp mppt controller. Now I'd like to size the roof panels so I only have to do it once. I have seen some LG 300 watt panels I can get locally for about $260 a piece.

            -Bill
            Last edited by Bigbillsd; 06-02-2018, 04:24 PM.

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            • #7
              Thick skin required if you want honest and real answers.

              First mistake is trying to use Amp Hours which is pretty much meaningless. It is watt hours you need to work with. Amp hours is just an end result of the design process. If you try to remove 200 AH from a 520 AH battery is a bit steep and leaves you nothing for cloudy spells.

              Assuming you are wanting 200 AH @ 12 volts I gather you are needing 2400 watt hours per day which is crazy high for an RV. Anyway to put back in 2400 watt hours requires the panels to generate 3600 watt hours. So the next piece of info you need is how many Sun Hours under worse conditions the panels will be exposed to. In an RV you have two strikes against you.

              1. Requires you to park the RV in full sun with no shade issues from sunrise to sunset. Good luck with that in a mobile oven called an RV.
              2. Derate Sun Hours with panels facing straight up.

              You did not mention time of year use or location but as an example lets say Albuquerque NM with the shortest month of October with 0 degree tilt gives you 4.5 Sun Hours vs 6.6 Sun hours with latitude tilt.

              Panel Wattage = Daily Adjusted Watt Hours / Sun Hours

              3600 wh / 4.5 sh = 800 watts.

              MPPT Charge Controller = Panel Wattage / Battery Voltage

              800 watts / 12 volts = 67 amps

              Battery AH Capacity = 3 to 5 day reserve capacity. If you select 3 days only gives you 2 days, and with 5 day reserve gives you 3 day run time without sun. On an RV you must have a generator with a battery charger or forget it. On an RV you can get away with 3 day reserve capacity.

              AH = Daily Watt Hours x 3 days / Battery Voltage

              2400 wh x 3 / 12 volts = 600 AH.

              So in an RV about the best you can do is charge your battery at minimum rate in your application with the Crown batteries. That happens to be 25 amps and with 2P is 50 amps. That makes things easy to find panel wattage. Your batteries charge range is 25 to 60 amps or 50 minimum up to 120 amps.

              Watts = Voltage x Amps, or 50 amps x 13 volts = 650 watts or higher up to 1500 watts. Good luck finding that much room on your RV parked in the hot sun. No problem right?
              MSEE, PE

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              • #8
                I had one in my old 1993 DP and it worked for years without any problem; to tune up for 8 years, not even a clean up !
                By memory, it was a GENERAC I think, it was a 5500 WATTS, the model is discontinued http://www.electricgeneratorsdirect....858/p5208.html


                BTW, if I had the chance to buy a newer dp, I'd gofor a full electric dp with a 8,000 WATTS quiet diesel generator like http://www.dieselgeneratortech.com/
                .

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