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Is my Calculation True for 60 Watt Off-Grid Lighthing ?

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  • #16
    Originally posted by malborn View Post
    I ordered the book from amazon Thank you.

    Because we are going to use MPPT and 24 volt and you mention MPPT requires 72 cell solar panel, Should we use 72 cell + 72 cell= 144 cell solar panel or 36 cell + 36 cell =72 cell solar panel ?

    I couldn't find 200 watt 72 cell 12 Volt solar panel to use?
    Most 72 cell panels have a Vmp ~ 36 volts. The battery (12v) panels have about 36 cells which gets a Vmp ~ 18 volts.

    Because most MPPT cc's have a higher DC input voltage rating you have the ability to wire multiple panels in series. With a PWM charge controller you are limited on the DC input voltage from the panel and usually have to wire them in parallel.

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    • #17
      Originally posted by malborn View Post
      Because we are going to use MPPT and 24 volt and you mention MPPT requires 72 cell solar panel, Should we use 72 cell + 72 cell= 144 cell solar panel or 36 cell + 36 cell =72 cell solar panel ?

      I couldn't find 200 watt 72 cell 12 Volt solar panel to use?
      72 total in series. Most all 200 wat GT panels are 72 cells. Battery panels are 36 cells and made for 12 volts. You would have to use two of them in series to make 36 volts and 72 cells. Do not use battery panels with MPPT as you are throwing away money.

      Just buy yourself two 200 watt GT panels with 72 cells and install them in parallel.
      MSEE, PE

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      • #18
        Originally posted by Sunking View Post
        72 total in series. Most all 200 wat GT panels are 72 cells. Battery panels are 36 cells and made for 12 volts. You would have to use two of them in series to make 36 volts and 72 cells. Do not use battery panels with MPPT as you are throwing away money.

        Just buy yourself two 200 watt GT panels with 72 cells and install them in parallel.


        Thank you very much

        It might not possible to be practical but lets say I am using mppt controller and 2 X 12 volt batteries which require 36 volt for charge itself. and my panel Vmp is 38 Volt, 60 cells. Because Vmp of panel is bigger than the required voltages by batteries Can I desing like that ?


        last question why do we need to use only 36 cell solar panel on pwm controller ? lets say I need 300 watt and my panels 36 cell 100 watts. How should I connect them ? If I connect them in series 36 + 36 + 36 = 108 cells which exceeds 36 cells ?

        btw I bought the solar book that you suggested to me on amazon

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        • #19
          Originally posted by Mike90250 View Post
          Several controllers have lighting functions, dusk - dawn. dusk +6 hours.....
          I use one of these controllers and it allows you to select how long after sundown to turn off the lights, therefore greatly reducing the size of battery bank and solar panels needed for a particular installation. Unless of course you wish the lights to run dusk to dawn, then you will pay double.
          4X Suniva 250 watt, 8X t-105, OB Fx80, dc4812vrf

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          • #20
            Originally posted by malborn View Post
            It might not possible to be practical but lets say I am using mppt controller and 2 X 12 volt batteries which require 36 volt for charge itself. and my panel Vmp is 38 Volt, 60 cells. Because Vmp of panel is bigger than the required voltages by batteries Can I desing like that ?
            OK you are kind of loosing me. [B]Are those two 12 volt batteries in series for 24 volts, or in parallel for 12 volts?[/B]

            A panel with 60 cells in series should only have a Vmp of around 30 volts which is too low for a 24 volt battery, but fine for a 12 volt battery assuming you use MPPT controller. Are you sure that 60 cell panel Voc is 36 volts and you mistaken it for Vmp. Voc and Vmp are two different ratings.

            Perhaps this might help. Regardless if the controller is PWM or MPPT you must have a minimum of 36 cells for every 12 volts of battery. So if you are indeed running 24 volt battery you must have at least 72 cells in series.

            With PWM no more and no less than 36 cells per 12 volts of battery. So if you have say 4 36 cell battery panels on a 12 volt battery they must be wired in parallel to maintain 36 cells. If 24 volts they would have to be 2 in series in parallel with 2 in series to maintain 72 cells.

            With MPPT you still need a minimum of 36 cells per 12 volt of battery. However depending on your controller could go as high as 100 cells or more. If you look at a MPPT controller it has a spec called Maximum Voc input. Small 15 amp controllers usually have a limit of 70 Voc, while others are 150, 200, 250, and up to 600 volts. But those are going to be you 80 amp controllers. You want to run as high of a voltage as possible to maximize efficiency.

            Originally posted by malborn View Post
            last question why do we need to use only 36 cell solar panel on pwm controller ? lets say I need 300 watt and my panels 36 cell 100 watts. How should I connect them ? If I connect them in series 36 + 36 + 36 = 108 cells which exceeds 36 cells ?
            Already answered that, In Parallel, not series. If MPPT then by all means in series if your controller can handle that high of a Voc. Prime numbers are BAD. You only have two options. All in series or all in parallel. Use whole numbers like 1,2 4, 6, 8, 9, 10, 12.....If you have a high voltage Controller of 150 Voc or higher you can get away with Prime number of 3 and 5 in series. But you effed yourself if you have say a 20 amp MPPT with 3 panels, as 3 could likely be more than 70 Voc limit of the controller. 1, 2, 4, and 6 work.
            MSEE, PE

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            • #21
              Thank you very much for very useful information. I combine this informations with the book you offered me It is very helpful

              Let's say my lighting is 60 watt led but 120 volt ac, should I use converter to convert 24 volt before connect to mppt controller ?

              I just found this product: does it work ? http://www.trcelectronics.com/View/M...APV-8-24.shtml

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              • #22
                Originally posted by malborn View Post
                Let's say my lighting is 60 watt but 120 volt, should I use converter to convert 24 volt before connect to mppt controller ?
                No you use a 24 volt Inverter connected to the batteries.

                Panels > Charge Controller > Battery > Inverter.
                MSEE, PE

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                • #23
                  Oh thank you I just got it your answer


                  I am so curious about that: Let's say I have:
                  36 volt dc light
                  2 x 12 volt panel (24 volt)
                  2 x 12 volt battery (24 volt)
                  can I connect them to charge controller directly without using converter ? If ı need to use dc to dc converter where should I connect ? between[B] load terminal of mppt and light[/B] or to [B]batteries[/B] ?

                  thank you

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