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  • Help to get the wattage of panels

    Hi everyone,
    I am new to this site. I recently made up 4 solar panels with 36 of 3x6 cells on each one of them. When I checked the volts in bright sun it produced 18- 19.5 volts. I need help to find how many watts my panels produce.Please if any one could let me know a simple way to do it.I tried with my digital multimeter to get check the amps. but it showed for an instant and now i can't get it any more.I would like to know why.

  • #2
    @ nman59 - Welcome to Solar Panel Talk!

    One of the guys who knows this kind of stuff should be along before long.

    Meantime, welcome to the forum.

    Russ
    [SIGPIC][/SIGPIC]

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    • #3
      measure volts, with no load, like you did.

      then measure short circuit amps, and record that.

      volts x amps = watts It will get you roughly the watts your panels can produce.
      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
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      • #4
        Without a MPPT tracking device (lab equipment) you will never obtain an accurate measurement. Best you can hope for is a ball park figure if you know what you are doing and fully understand electrical theory.
        MSEE, PE

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        • #5
          sunking

          [COLOR="blue"]Without a MPPT tracking device (lab equipment) you will never obtain an accurate measurement[/COLOR][COLOR="black"]I have measured the output of panels with nothing more than a volt meter and have found the reading taken of the panel in midday sun gives same result as when the panel is connected to a charge controller and a battery,,[/COLOR]
          I think if the answer you get doing it the simple way is within a few % its perfectly ok as no panel is ever opperated at all times under optimum condiitions anyway..
          Most people dont need lab standard answers as it cant be reproduced when in nornal use.

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          • #6
            Originally posted by Mike90250 View Post
            measure volts, with no load, like you did.

            then measure short circuit amps, and record that.

            volts x amps = watts It will get you roughly the watts your panels can produce.
            Not really. Using Voc and Isc are excellent measurements if you have the spec to compare them too. For a home made unit, not so sure it means a lot.

            For example for a 36 cell BP model number BP3110 is a very popular moncrystaline 110 watt solar panel made for the 12 volt battery market. Its specs are

            Voc = 22.1 volts
            Isc = 7.4 amps
            Vmp = 17.0 volts
            Imp = 6.5 amps

            If you used the Voc and Isc to get an idea to determine how much power it should generate would give you 163 watts. When using true operating specks Vmp and Imp give you 110 watts STC. Quite a bit of difference.

            Only thing i can tell from the OP question and statement is if he is measuring a Voc of 18 volts with 36 monocrytaline cells, something is wrong to start with as it should be up around 22 to 24 volts.
            MSEE, PE

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            • #7
              Originally posted by nman59 View Post
              Hi everyone,
              I am new to this site. I recently made up 4 solar panels with 36 of 3x6 cells on each one of them. When I checked the volts in bright sun it produced 18- 19.5 volts. I need help to find how many watts my panels produce.Please if any one could let me know a simple way to do it.I tried with my digital multimeter to get check the amps. but it showed for an instant and now i can't get it any more.I would like to know why.
              Did you simply set the meter to Amps and put this directly across the output of the panel? If so you may have blown a fuse (or worse) in the meter. What current is the meter rated for?


              Steve

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              • #8
                to calculate the power output of your panel you would typically, put meter onto volts setting across your positive and negative leads going into your charger, put a clamp style ammeter onto one of the leads and then multiply the answers to get total watts produced by the panel. eg, your voltage may read 15v, the current may read 4A , the power would be 15V* 4A = 60 Watts power produced. take various measurements and the highest in best sun will be peak output

                as you will likely not have a clamp style ammeter the next best thing is a simple analogue panel ammeter, a break is made on the negative lead going to charger for example, and the meter inserted into the break, so the meter is connected in series.

                a multimeter is great for the voltage testing, but not for continuous current testing, in order to find your peak power output

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