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  • Upgrading to 24v????

    I am new to solar as I bought 2 acres in the smokey mountains TN. Started with a 50w panel and Pwm 10a,p CC, living in rv for next 8-12 months while I clear and prepare to build. There is no AC electrical power here and probably never will be. So I will always be coming here for info. Thanks.
    I have upgraded to currently having 2-250w PV's, a Renogy 12/24-20/40 MPPT CC, 6-12v 100ah batteries running a 12v system. Iam upgrading it to a 24v system and am needing some help from people who know there stuff, as why I'm here.
    I currently use about 150 watts maxx per hr X 12hr maxx day= 1800 watt hrs day with nightly generator use on hot nights for AirCond.and 8 amp charger to fill batts back to around 13.7v
    I am upgrading to 24v and with the info I supplied could yall just plain out tell me how many total 12v batts and total # of 250w panels I will need for the 1800 watt/day with 2 day reserve. Also how to wire the PV's together AND wire the batts either series or diagonal series. Any diagrams would greatly be appreciated. Thanks guys and galls.
    Last edited by Jnj6370; 08-22-2016, 11:32 AM.

  • #2
    A good start would be to read the sticky threads in the Off Grid section of the Forum. There are descriptions and spreadsheets to help you do exactly that design process.

    For wiring, start with http://smartgauge.co.uk
    Last edited by inetdog; 08-22-2016, 01:57 PM.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      I've been reading for the last 3 hours, also looked through the 20 pages of topics in the off grid fourm. Let me ask this question maybe someone knows the answer. Are panels 250 watt and over considered grid tie? Also my panels have Voc of 37 and my CC has max of 150 v. It's a Remogy commader series 12 or 24v. Can I wire my panels whether I have 2 panels or 3 or 4 in parralel OR series and not cause damage? I had rather have extra panel since winter and gray days are coming. If I loose energy produced with 4 panels and loosing energy that could have been stored but don't have enough batteries is ok for now as every month I buy 2 batteries. Just thought there were people here that could have answered my question in there sleep. I didn't think that my question was top secret or that people thought I was to lazy to search forum's and stickys .
      Last edited by Jnj6370; 08-26-2016, 04:32 AM.

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      • Wy_White_Wolf
        Wy_White_Wolf commented
        Editing a comment
        The voltage is what tells us they are grid tie panels. You will have to run them with at least 2 in series to have the voltage high enough for a 24v system. With the MPPT charge controller 3 would be better. That would put your VOC at about 111V so easily handled by the charge controller.

        The battery bank should be 375AH @ 24V to handle 1800Wh a day. Really need your location to determine the array size but am guessing by the battery bank it needs to be in the 800 to 1000 watt range for size.

        WWW

    • #4
      Originally posted by Jnj6370 View Post
      I've been reading for the last 3 hours, also looked through the 20 pages of topics in the off grid fourm. Let me ask this question maybe someone knows the answer. Are panels 250 watt and over considered grid tie?
      No. PhotoVoltaic panels are themselves simply the panels that make electricity from sunlight.

      Grid-tie: whether net-metering, or tarriff, or simple grid-assist are all determined by how your system is designed. If you want a pre-wired certified system it would be called your E-panel.



      4400w, Midnite Classic 150 charge-controller.

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      • #5
        Thanks everyone. Mr. white thank you as that was the exact answer I was looking for. So an single string of 8 100ah wired in series making 1 400 ah battery,coupled with the CC I mentioned above with 3-250w panels w/ 37Voc wired in series would make a happy solar family?
        I'm going to ask this question as I am ignorant of solar but really trying to learn, would it be better off wiring 4 panels in series for really bad winter days where I might only have 2 hrs max to get my power! And when summer comes next yr add more batts to go w/more sun? I'm thinking that would work but just like to hear it from someone who knows.
        Thanks y'all
        .

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        • #6
          A string of 8, 6V 100ah batteries would yield a 48V 100ah bank. And it would have a lot of watt hours in it,
          In SERIES Voltage adds
          In PARALLEL, Amps add

          More realistically, using 8 cheap 6V Golf Cart 200ah batteries in series, gives 48V @ 200ah or 9600 watt hours Wiring the PV panels to 80 - 111V would be great for charging them,
          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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          • #7
            Originally posted by Jnj6370 View Post
            . So an single string of 8 100ah wired in series making 1 400 ah battery,coupled with the CC I mentioned above with 3-250w panels w/ 37Voc wired in series would make a happy solar family?.
            No only half right. 1 million 100 AH batteries wired in series is 100 AH. I can only assume you are using 6 volt 100 AH batteries? Or are they 12 volt 100 AH batteries. Makes a huge difference. If wired in series you would have 48 Volts @ 100 AH using the 6-Volt batteries, and 96 Volts @ 100 AH. Remember this formula:

            Battery Capacity = Battery Voltage x Battery AH = Watt Hour Capacity.

            Remember Two Laws. You cannot change or violate physical laws.

            Series Circuit Law: all current flowing through in the circuit are equal through all components and voltage across the circuit is the SUM of each component, and Power Adds. In English Current stays the same, voltage and power adds.

            Parallel Circuit Law T

            or more circuits are connected in parallel they have the same potential difference voltage across their ends. The total current is the sum of the currents through the individual components, in accordance with Kirchhoff current law. Power adds. In English Current Adds, Voltage is Constant, and Power Adds.

            So if you think about what was just defined, you might notice one thing is in common with both parallel and series circuits is POWER ADDS. Don't get to hung up on voltages and current. That is just the end result or minor details. OK so assume you have 8 of the 6-volt 100 AH batteries. To you right now only means some voltage and current, it tells me you have 4800 watt hours. Each battery has 6 volts x 100 AH = 600 Watt Hours x 8 batteries = 4800 Watt Hours.

            What Voltage is that? You tell me as you can pick from

            48 volts @ 100 AH,, 8S = 4800 wh
            24 Volts @ 200 AH, 4S2P = 4800 wh
            12 volts @ 400 AH, 2S4P = 4800 wh
            6 volts @ 800 AH 8P = 4800 wh

            Does not matter how you arrange them, it comes out to 4800 wh.

            Originally posted by Jnj6370 View Post
            .I'm going to ask this question as I am ignorant of solar but really trying to learn, would it be better off wiring 4 panels in series for really bad winter days where I might only have 2 hrs max to get my power! And when summer comes next yr add more batts to go w/more sun? I'm thinking that would work but just like to hear it from someone who knows.
            Thanks y'all
            Highest voltage as you can run.
            MSEE, PE

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            • #8
              I recommend going all the way - right to a 48Vdc system as you will eventually want to be there and 12V and 24V inverters can't be upgraded. You'll get twice the productivity out of your charge controllers and inverters, batteries will last longer, and the system will be more efficient in general running at higher voltages. Will cost more initially, but in the long run - you will be way ahead....
              BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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              • #9
                Originally posted by Jnj6370 View Post
                I currently use about 150 watts maxx per hr X 12hr maxx day= 1800 watt hrs day with nightly generator use on hot nights for AirCond.and 8 amp charger to fill batts back to around 13.7v.
                Getting back to your question with a direct answer. First forget the AC on Solar. That will have to stay on generator. Having said that why on earth would you want solar?

                You are running the genny every night to stay cool right? Why not just buy a properly sized charger and battery, and forget Solar. Assuming 2 Kwh usable would require:

                24 Volt @ 400 AH battery, or 48 Volt @ 200 AH.
                Charger = 40 Amp @ 24 volts, or 20 Amp @ 48 volts

                If you insist on solar then use 1000 Watt Panel system, with a MPPT controller same size as Battery Charger. .

                Here is what it boils down to. Battery Cost are fixed. Example using 4 Trojan J200-RE 12 volt 200 AH batteries is going to cost $1100 with or with out solar. A good charger will cost you $300 to $500. So around $1300 to $1500 using the genny.

                Want Solar? Add another $2000 to $3000 on top of that for Panels and Controller. You are looking at $4000 your way. .

                Take your pick. Either way you need a good charger to maintain your batteries. 8 Amps is not going to cut it.
                Last edited by Sunking; 08-23-2016, 01:47 PM.
                MSEE, PE

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