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  • Hi guys, trying to reconfigure an off grid setup

    Thanks for letting me join.

    I'm from Victoria, Australia.

    I'm attempting to assist a friend who has been living off grid for a few years now, and is having issues with the solar setup which he installed himself.

    After seeing his configuration, panels all running in parallel, 12v batteries all running in parallel, I'm hoping you guys can give some pointers on the most efficient setup.

    he has;
    5 x 200w panels
    9 x 100w panels
    1 x midnite classic 150
    2 x powerjack 100a controllers (these claim to be mppt but i seriously doubt it)
    1 x chinese 12v dc 3000w generator
    2 x 2000w inverters
    New batteries being delivered in a few days are 8 x 12v 100ah


    12v devices in house:
    12 x led downlights (running 2 to 3 at a time is normal)
    1 x Water pressure pump
    1 x refridgerator with a danfoss compressor (5 amps when running)

    240v ac devices in house:
    2 x moderate/small sized lcd televisions
    Fetch set top tv box
    modem/router
    1 x laptop
    2 x phone chargers
    2 x tablet chargers

    there's most likely a few small things i may have missed, but they'd me minimal.

    the problems he's having at the moment are battery related. After seeing his install and configuration, I'm sure i heard baby jesus cry a little.

    his old batteries are cactus, and I'm sure he could get a longer service life out of a new batch, with a bit of reconfiguration.

    i thought i new some basics in the area prior to reading the information here, any direction would be appreciated, as he seems to be biting his own tail.

    cheers
    ​​​​​

  • #2
    Wow, what a mess.

    First off, start at the beginning. Figure out what his loads are - wattage per load and more importantly watt-hours a day.

    Next switch to 48V. 12V batteries are the wrong battery for this application, but 2 strings of 4x12V isn't _too_ bad.

    Next get the appropriate charge controllers to allow series connection of the two strings. Not sure what the panel specs are so I can't guess at what would work here, but it's going to be awkward with the panel assortment he has. 2 4-panel strings on one controller and 1 5-panel string on the other might work. (Sell the 9th panel.)

    If he wants to keep the 12V loads get a DC/DC to drop 48 to 12V. Rewind or otherwise reconfigure the generator for 48V. He will need new inverters.

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    • #3
      Thanks for the feedback jflorey.

      without my meters on site, I'm only guessing that his daily usage would be less than 10kw/h.
      With a peak of approx 1.5kw.
      but these estimates are yet to be confirmed.

      but even with these estimates, i think he'll need at least double the battery capacity, feel free to correct me if I'm wrong.

      I'll have a go at the 2 x 4 panel string setup on the midnite classic. either controller has only inputs for 1 string, would it be ok to parallel the 2 strings? Or am i better off getting a combiner?

      since the batteries are 12v, is it bad practice to have them in series to 48v, and at the same time drawn from at 12v using high amp diodes?

      in regards to the generator, I'm not sure if it would be worth the effort to reconfigure, I'll start researching a 48v unit.

      cheers
      ​​​​

      Comment


      • #4
        Originally posted by Xagtho View Post
        without my meters on site, I'm only guessing that his daily usage would be less than 10kw/h.
        With a peak of approx 1.5kw.
        but these estimates are yet to be confirmed.
        You have an abortion on your hands to clean up. There is no way you are going to generate 10 Kwh usable with the panels or batteries. 12 volt parallel anything is one messed up system and just plain ignorant.

        You are going to need at least 3000 to 4000 watts of panels wired in series at high voltage, into a 48 volt 1000 AH battery You are no where close. A If you were to configure the batteries as 48 volts is only 200 AH or 1/5 of what is needed.

        MSEE, PE

        Comment


        • #5
          Originally posted by Sunking View Post

          You have an abortion on your hands to clean up. There is no way you are going to generate 10 Kwh usable with the panels or batteries. 12 volt parallel anything is one messed up system and just plain ignorant.

          You are going to need at least 3000 to 4000 watts of panels wired in series at high voltage, into a 48 volt 1000 AH battery You are no where close. A If you were to configure the batteries as 48 volts is only 200 AH or 1/5 of what is needed.
          Fair enough

          as stated, I'll know more when metered, but was over estimating for the worst case scenario.

          forgive my ignorance, but how is 12v in parallel ignorant?

          thanks for your battery capacity estimations, seems that the online battery calculator i was using is incorrect; Lead Acid Sizing

          10kWh x 2 (for 50% depth of discharge) x 1.2 (inefficiency factor) = 24 kWh


          24 kWh = 500 amp hours at 48 volts → 500 Ah x 48V = 24 kWh


          And thanks for the panel wattage requirements also, it looks as if my worst case scenario of kw/h was too high, it's good to be able to work back towards the easy end.

          Comment


          • #6
            Originally posted by Xagtho View Post
            10kWh x 2 (for 50% depth of discharge) x 1.2 (inefficiency factor) = 24 kWh[/h] 24 kWh = 500 amp hours at 48 volts → 500 Ah x 48V = 24 kWh
            No if you discharge 50% per day you will destroy the batteries quickly and just one cloudy day you are shut down and dark for 2 days to recover and recharge. You size the batteries for 5 day reserve which gives you 3 days or run time and will maximize battery life. Battery Amp Hour = Daily Watt Hours x 5 / Battery Voltage. 10 Kwh x 5 / 48 volts = 1041 AH.

            If you parallel batteries you are significantly shortening cycle life. Compound by discharging 50% per day and you have a 1 year or less battery. So if you need 1000 AH batteries you buy 1000 AH batteries and they will not be 12 volts. Such a beast would weigh 800 pounds, and is why you do not find large 12 volt batteries. You would use 2 or 4 volt batteries.


            Originally posted by Xagtho View Post
            And thanks for the panel wattage requirements also, it looks as if my worst case scenario of kw/h was too high, it's good to be able to work back towards the easy end.
            Well here is what you are missing. Example lets say you need 4000 watts of panels. Try that at 12 volts will require 4 very expensive 80 amp Charge Controllers and wire as big as your wrist to handle 320 amps of current. Not only extremely expensive but very dangerous, prone to outages/failures, and extremely inefficient. Use 48 volt battery and you only need 1 expensive 80 amp controller and much smaller wire. 1/5 the cost, much safer, less prone to failures, and 1600% more efficient than 12 volts.

            So if you used the 12 volt 100 AH batteries would require 40 batteries. You could configure them 40P at 12 volts or 4S10P. Either way is an abortion. Correct configuration is using 4 volt 1000 AH batteries configured 12S for 48 volts.

            I assume this friend has a nice large 8 to 10 Kw generator? You must have a generator and charger to maintain the batteries and cover your arse during cloudy spells. I dare you to find find a 12 volt 400 amp charger. They do not exist. You can easily find 48 volt 100 Amp chargers and up.
            Last edited by Sunking; 05-22-2018, 07:22 PM.
            MSEE, PE

            Comment


            • #7
              Wow! Hi guys. I'm new here too. As one guy already mentioned on this thread...."What a mess." That's a lot going on. I'd try to narrow it down to just what the average kW per day us is and what the peak kW per hour use it. Since he has the panels, that's a start. Get rid of the 12V Chinese Generator and 2 200w inverters. I saw a video on YouTube where a guy had a lot of panels on one inverter run an A/C unit of 1.5kW on an inverter/charger. Personally I'd DC couple it, but the inverter is fairly new and this is the first inverter without batteries I've seen run an A/C unit. Hoping to learn more from this channel and looking forward to sharing ideas that I'm not familiar with. So hello everyone and thank you ahead...

              Comment


              • #8
                Originally posted by Metalfiber View Post
                Wow! Hi guys. I'm new here too.
                Hi Metalfiber, and welcome to SolarPanelTalk. Switch from advice-giving mode to learning mode for awhile, and no more youtube links, it's the mother lode of the kind of bad/dangerous misinformation that isn't tolerated here. Just read and ask questions, and no more talk of DC-coupling.

                Comment


                • #9
                  Originally posted by Metalfiber View Post
                  the average kW per day us is and what the peak kW per hour use it.
                  This makes no sense, do you mean KWH per day, peak KW (NOT per hour)? Bruce Roe

                  Comment


                  • #10
                    Originally posted by Metalfiber View Post
                    Wow! Hi guys. .
                    That is the only thing you have said that is a true statement. The rest is baby gibberish nonsense.

                    MSEE, PE

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