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Help me work out why I'm getting way less AH out of my PV array than I should!

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  • Help me work out why I'm getting way less AH out of my PV array than I should!

    This has been driving me bonkers, I've done so much reading but are no closer to a solution. So I thought I'd turn here and see if someone can help.

    Background / Overview

    The solar site is on a hill, with a very clear view of the sky, there is nothing obstructing it.
    The constant load on the site is 7 amps @ 24v (168w). This can flucuate +/- 3w but is pretty constant 24/7/365. It drives some radio equipment that has a constant draw.

    I'm in New Zealand.

    Equipment

    Batteries - 4x 271ah (that's their 20h rating, their 100hr rating is 335ah) Nomad E2 Ultra AGM batteries. These are wired 2 x series and 2 x parallel to give a total output voltage of 24v.

    Charge Controller - Outback Flexmax 80. I just plugged in a Mate3 today.

    PV Panels - 8x 250w TNSolar TN250P-60 solar panels. These are wired as two banks in parallel, each bank consisting of four panels in series.

    Settings

    Absorb voltage - 29v
    Absorb time - 7h
    End amps - 10 amps
    Rebulk voltage - 27.6v
    Float - 27.6v
    No equalisation setup or ever been run.
    MPPT Mode - Auto
    MPPT Sweep Mode - Half
    Max Sweep - 90%
    UPICK Percentage - 77%
    Restart Mode - 0


    Can anyone see anything in that that might cause it to get such a low AH, like today it only drew in 83AH, it was a little bit cloudy this morning, but clear most of the day (very rarely a cloud would pass), the temperature was around 15-20c max. The panels are clean as, and no blown fuses. There has been the odd day it's pulled through a lot, every couple of weeks it may get upto 200ah or so, but that's rare.. some days 140-160ah. But often below 100ah.

    I have three sites setup similar. The other two sites, that I have no issues with, have 4 batteries wired the same way as below, only 6 panels (3 in series to make 2 banks of parallel), but they only draw 2.5amps constantly. They never dip below 25.2v even in the middle of the night regardless of weather.

    I've posted a comparison of the two sites charging from today. The number on the left is the voltage x100, so for example 2485 is 24.85 volts.

    Good charging site
    Good Site.jpg

    Bad site
    Bad Site.jpg

    As you can see between 11:30am - 4:30pm the site didn't charge at all, as the voltage steadily dropped as it does overnight. Which is weird as that was pretty good charging conditions.

  • #2
    At first glance three possible causes come to mind:

    1. There is something wrong with the wiring of the panels which is causing intermittent connections, especially during the heat of the day.
    2. There is something wrong with at least one panel in each string which is causing the output power to drop or restricting current from the whole string. (The latter would imply a bad (open circuit) bypass diode.
    3. A problem with the Outback CC.

    To systematically troubleshoot the problem, I would want to see voltage and current (DC clamp-on ammeter) on each string both when charging and when charging has stopped unexpectedly.

    Let's add a fourth longshot possibility: intermittent shade from temporary obstacles (bird resting on panel, etc.)
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by inetdog View Post
      At first glance three possible causes come to mind:

      1. There is something wrong with the wiring of the panels which is causing intermittent connections, especially during the heat of the day.
      2. There is something wrong with at least one panel in each string which is causing the output power to drop or restricting current from the whole string. (The latter would imply a bad (open circuit) bypass diode.
      3. A problem with the Outback CC.

      To systematically troubleshoot the problem, I would want to see voltage and current (DC clamp-on ammeter) on each string both when charging and when charging has stopped unexpectedly.

      Let's add a fourth longshot possibility: intermittent shade from temporary obstacles (bird resting on panel, etc.)
      Hi inetdog,

      Thank you for the very quick reply

      1) The wiring was done by a electrician and is using all the proper solar connection plugs then through the fuses and circuit breaker back to the CC. Now obviously this doesn't mean there isn't a problem, as wiring is one of the next things on my list to check. It's more just meaning it's not some slapped together home job
      2) Good thought, I might make up a test lead and test each panel individually when the sun is at its peak, though thinking about it I might need to test them in pairs to get the voltage > battery voltage to instigate charging.
      3) I have a spare, I did wonder about swapping it over, so I might make that tomorrows job when I take more fuel up for the generator.
      4) Possibly unlikely, there is no where for them to rest apart from along the top and it's unlikely they'd shade anything if they did due to the angle.

      Does the PV array look adequately sized to you?

      Comment


      • #4
        Originally posted by inetdog View Post
        At first glance three possible causes come to mind:
        Ok so the comparison good site, started the day with the battery banks around 25.2v, then reached absorb charge of around 29v fairly quickly, stayed there most of the day..

        The bad site, I run the generator charger at for 11 hours overnight while it was dark.. I've noticed whenever I use the 24v charger it only ever seems to draw around 20-25 amps, even though it's capable of uptop 75 amps.
        This meant about 7am this morning before the PV panels kicked in it was at 25v exactly.
        It was in an out of absorbintion mode all day, when I went upto it around 1pm it was only pulling about 15 amps including the load (load is 7amps).. that means it was trying to put around 2amps into each battery. Does this sound right? seems bugger all. It looks like it really stopped charging about 2:30pm, where as the good site was well into absorb mode then.

        When I log in just now at 5pm with the Mate 3 it says the status of the charge is "silent". The good site is still charging (it's plenty sunny outside).

        So I'm of the conclusion the batteries just don't want the amps in them. They're about 4 months old.

        I also replaced the CC with an identical one, both are setup exactly the same as the good site.

        Comment


        • #5
          Hi BpNz ,

          Fellow Kiwi from Alexandra,

          Did you resolve the problem you were having,
          I am having similar problem with identical branded batteries in a 12v system wired in parallel also running a personal solar repeater. but only drawing 1.5amps
          What was the resolution to your problem. Might help me with my situation.

          Cheers Jeremy

          Comment


          • #6
            Originally posted by Jeremynzl View Post
            Hi BpNz ,

            Fellow Kiwi from Alexandra,

            Did you resolve the problem you were having,
            I am having similar problem with identical branded batteries in a 12v system wired in parallel also running a personal solar repeater. but only drawing 1.5amps
            What was the resolution to your problem. Might help me with my situation.

            Cheers Jeremy
            Hey Jeremy, my apologies.. I just spotted you question as hadn't logged in in a long time.. do you have an email address? as I'd be keen to chat.. thanks

            Comment


            • #7
              Could he have lost one whole string of four panels? Perhaps in a manner that made it into a light load for the good string?

              Comment

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