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  • Off grid system advise wanted rework?

    Hello
    looking for advise or instruction on adding on to and re working what i have.

    Originally i bought a Renogy 800w 8x 12 volt mono panels deluxe kit with commander 60 amp mppt controller.
    I set this up with 4x 6 volt 235ah batteries @ 12 volts. Panels are wired as 2 strings of 4 series and parallel 48 volts? link to wiring diagram https://www.renogy.com/renogy-new-80...r-premium-kit/

    Then the exact same set up fell in my lap for very little cost. so since middle of Maine winter i set it up the same way and bought 2 more batteries for a bank of 705AH and the system has been great... batteries are charged by noon with my intended load and around 2pm on cloudy days.

    So in total i have
    16 x 12 volt Renogy mono panels divided between 2 controllers feeding one battery bank
    2 x commander 60 amp controllers
    6 x 235ah 6 volt batteries
    fuses all in place
    all 3 mos old

    Now while i understand wiring batteries, i'm not so sure i understand the wiring of solar panels outside of the instructions i was given and if what i would like to do is safe or to much for the controllers, Since i know both controllers are maxed out now at 12 volts 800 watt max with 100 volt limit?

    My plan is to add 2 more 6 volt 235ah batteries and rewire for 24 volts 2 strings of 4. i think is correct. and then add 4 more panels of same type.

    My biggest question is once the batteries become 24 volts. what is the best way to add more panels? do i create another string of 4 for 12 panels on one controller 8 on the other or do i add on to a current string of 4 and make 6 panels in a string?
    The controller can do Max. Solar Input Power: 800W (12V), 1600W (24V), 2400W (36V), 3200W (48V)

    About the only reason were looking at change is because for power outages we would like to know we can run our refrigerator and well pump and 24 volt seems better suited. Right now we run tv's, lights,pellet stove. but would also like the bit of extra storage and take advantage of the power were not using. were up to about 60 % off grid at this point and want to further. all tho my gut tells me to leave the system alone and just add the 2 extra batteries I cant help but think there is a better way.and still keep the system balanced. what would you do? TIA

  • #2
    24V systems can require up to 33V to be properly charged. Not sure about the Renogy controllers, but generally you are good to use 2x battery charge voltage, for the solar MPPT voltage, so something in the 60 - 70Vmp ballpark would work.

    Being up north, you have to watch your cold weather Voc and be sure it will not fry your controller @ 100V 3 panels in series sounds about right, but only you can insure that is below the kill voltage of your controller. 4 panels in series is going to be too close to the 100V kill limit
    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

    Comment


    • #3
      Originally posted by wrassie86 View Post
      6 x 235ah 6 volt batteries
      Does not work. That only gives you two options and neither are workable. With 6 x 6 volt batteries only gives you either 12 or 36 volt system, and that is the last thing anyone wants. You want either 24 or 48 volts. You would have to loose two batteries for 24 volts, or gain two batteries for 48 volts. Plan B is buy 2 more batteries and choose either 24 or 48 volts.

      With 1200 watts of panels only requires 1 controller. 50 amps @ 24 volt battery, or 25 amps @ 48 volt battery. With a single 60 amp controller you can go up to 1500 watts @ 24 volt battery, or 3000 watts @ 48 volt battery. Choose carefully.
      Last edited by Sunking; 03-02-2019, 10:50 PM.
      MSEE, PE

      Comment


      • #4
        Originally posted by Mike90250 View Post
        24V systems can require up to 33V to be properly charged. Not sure about the Renogy controllers, but generally you are good to use 2x battery charge voltage, for the solar MPPT voltage, so something in the 60 - 70Vmp ballpark would work.

        Being up north, you have to watch your cold weather Voc and be sure it will not fry your controller @ 100V 3 panels in series sounds about right, but only you can insure that is below the kill voltage of your controller. 4 panels in series is going to be too close to the 100V kill limit
        Mike, Thanks for responding, According to Renogy the panel system is wired for 48 volts, 2 strings of 4 for 8 panels each controller and how they sell and say to wire the system whether 12 volts or 48 volts battery bank. The commander 60 is/was there flagship controller (not cheap by any means) so i would hope they would not give instructions that would blow up controller ( but you never know) Any way in motoring the system after fresh snow fall and ultra clear sky's the highest ive seen the Voc hit was 88 and can regularly pull 25 plus amps per controller under load. Ive not tried to fully load the system yet. nor have the pc program hooked up for monitoring the controllers logs guess i should do that.

        panel specs
        [TABLE]
        [TR]
        [TD]Maximum Power at STC: 100W[/TD]
        [TD]Maximum System Voltage: 600V DC (UL)[/TD]
        [/TR]
        [TR]
        [TD]Optimum Operating Voltage (Vmp): 16.4V[/TD]
        [TD]Open-Circuit Voltage (Voc): 21.1V[/TD]
        [/TR]
        [TR]
        [TD]Optimum Operating Current (Imp): 6.1A[/TD]
        [TD]Short-Circuit Current (Isc): 6.6A[/TD]
        [/TR]
        [TR]
        [TD]Weight: 14.3lbs[/TD]
        [TD]Dimensions: 41.6 X 20.7 X 1.38 In[/TD]
        [/TR]
        [/TABLE]

        Comment


        • #5
          Originally posted by Sunking View Post
          Does not work. That only gives you two options and neither are workable. With 6 x 6 volt batteries only gives you either 12 or 36 volt system, and that is the last thing anyone wants. You want either 24 or 48 volts. You would have to loose two batteries for 24 volts, or gain two batteries for 48 volts. Plan B is buy 2 more batteries and choose either 24 or 48 volts.

          With 1200 watts of panels only requires 1 controller. 50 amps @ 24 volt battery, or 25 amps @ 48 volt battery. With a single 60 amp controller you can go up to 1500 watts @ 24 volt battery, or 3000 watts @ 48 volt battery. Choose carefully.
          While the system works great in the configuration is now. I know it is not optimal. My plan is plan B adding 2 more batteries. hope to have by the end of the week, while batteries are plentiful during the summer, not many golf carts going in the winter.

          But while i needed to ask these questions to try and fully understand, i found a post from you awhile back that made me question how i was doing things or about to do things. As of now i can run my daily loads currently around 200-300 watts from 8 am to 11pm and batteries are usually at float by noon to 2 pm the next day. at end of night batteries are at 12.5 volt and rebound up a bit.

          Now if i add the 2 batteries and go for 24 volt will my 16 panels still be enough? In reading a past thread you answered to some one else to i came to the conclusion that if i set up a 48v bank i would not have close to enough panels to fully charge in a day, while at 24 volts i'm borderline for the shortest days of winter. I have 0 issue buying the 2 extra batteries since i had planned to anyway. nor do i have a problem buying 4-8 more panels if this will keep me charging as i am now. and split panels between the 2 controllers or how ever would be the proper way to do this. TIA

          Also here is specs for my controllers


          [B]Renogy 60A Commander MPPT Solar Charge Controller[/B]
          Nominal System Voltage: 12v/24v/36v/48v/ Auto Recognition
          Max. Solar Input Power: 800W (12V), 1600W (24V), 2400W (36V), 3200W (48V)
          Rated Battery Current: 60A
          Grounding: Negative
          Max. Solar Input Voltage: 150VDC
          Self-consumption:1.4W to 2.6W
          Max. Input Short Current: 75A
          Communication: RS485 Cable
          Max. Terminal: 35mm2
          Temp. Compensation: -3mV/
          Last edited by wrassie86; 03-03-2019, 11:44 AM.

          Comment


          • #6
            Battery voltage does not effect the ability to charge them. Example let's say 4 x 12-volt 100 AH batteries. You could configure them as 12, 24, or 48 volts. Either way still requires the exact same amount of panel wattage. Each batteries is 12 volts x 100 AH = 1200 watt hours. so it makes no difference how you configure them will give you the exact same amount of capacity.

            12 volts x 400 AH = 4800 wh
            24 volts x 200 AH = 4800 wh
            48 volts x 100 AH = 4800 wh

            All three configs require 500 watts of solar panels minimum. What changes is controller size and wiring. With 12 volts would take a 40 amp controller, 20 amps @ 24 volts, and 10 amps @ 48 volts. So you have 1600 watts of panels. That means you need at least 24 volts @ 640 AH or 48 volts @ 320 AH batteries. So with 8 of the batteries. would give you either;

            24 volts @ 470 AH
            48 volts @ 235 AH

            With 1600 watts you will be charging at C/8 which is OK and meets the minimum of C/10. It will work.
            MSEE, PE

            Comment


            • #7
              @ SunKing Huge Thanks for clearing that up for me! Thats what i get for reading to much and asking no questions...

              So after re looking at the specs for my controllers they have a 150v max and not the 100v max i was told by a renogy tech? just wanted to make sure i was looking at the right spec of (Max. Solar Input Voltage: 150VDC)

              Also while i have ordered the 2nd set of batteries today due in by Friday,. I do still have one of my original questions of. If i decided to add 4 more panels mostly just for winter charging, would i just be able to create another string of 4 panels for 3 strings of 4 panels? TIA

              Comment


              • #8
                Originally posted by wrassie86 View Post
                @ SunKing Huge Thanks
                You are welcome.

                Also while i have ordered the 2nd set of batteries today due in by Friday,. I do still have one of my original questions of. If i decided to add 4 more panels mostly just for winter charging, would i just be able to create another string of 4 panels for 3 strings of 4 panels?
                I do not have enough information to answer your question. Help me help you. [B]What manufacture and model number battery do you have?[/B]

                Where I am going with this is batteries have minimum and maximum charge rates they can accept. I do not know what that is for your batteries without knowing make/model.
                MSEE, PE

                Comment


                • #9
                  Originally posted by Sunking View Post

                  You are welcome.



                  I do not have enough information to answer your question. Help me help you. [B]What manufacture and model number battery do you have?[/B]

                  Where I am going with this is batteries have minimum and maximum charge rates they can accept. I do not know what that is for your batteries without knowing make/model.
                  I've been able to get these local. And all the info i was able to find. i believe they are made by Deka but not positive as the item number belongs to batteries plus. If needed i can see about getting a data sheet from batteries plus tomorrow.[LIST][*][B]Item Number:[/B] SLIGC125[*][B]Brand:[/B] Duracell Ultra[*][B]Voltage:[/B] 6[*][B]Format:[/B] BCI Group GC2[*][B]Lead Acid Type:[/B] Deep Cycle[*][B]Battery Type:[/B] Basic[*][B]Capacity 20hr:[/B] 235AH[*][B]Chemistry:[/B] Lead Acid[*][B]Lead Acid Design:[/B] Flooded[*][*]After a bit more digging they are east pen/ deka BCI Group Size:GC2 part number HPGCX duracell I was able to find the spec sheet with that part number
                  20 amp hour rate:235
                  5 amp hour rate:188
                  Minutes at 25 amps:488
                  Minutes at 75 amps:132
                  Volts:6[/LIST]
                  Last edited by wrassie86; 03-03-2019, 07:42 PM.

                  Comment


                  • #10
                    OK as I suspected they are a low end gokf cart battery and those can take higher charge rates. I am comfortable in saying up to C/6. So if you have 8 units, than can handle up to 2000 watts. Having said that they need a minimum of 1000 to 1200 watts.

                    What you want to look out for is water usage. If you find yourself having to add water every couple of weeks, you know you have a charing issue like too much or voltage set too high. Get yourself a good hydrometer and learn how to use it.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      OK as I suspected they are a low end gokf cart battery and those can take higher charge rates. I am comfortable in saying up to C/6. So if you have 8 units, than can handle up to 2000 watts. Having said that they need a minimum of 1000 to 1200 watts.

                      What you want to look out for is water usage. If you find yourself having to add water every couple of weeks, you know you have a charing issue like too much or voltage set too high. Get yourself a good hydrometer and learn how to use it.
                      So far my water usage has been slight , I have been checking them the first of the month for the last 3 mos and only needed to add water last month and really the water was still well above the plates none needed the other day. i do have a hydrometer but it is crappy swing arm, will be ordering better glass one.

                      As i still think about the final voltage of 24 or 48 volt. I cant help but notice the inverter selection for 48 volts is slim/ pricey, most units are for really big power usage and not many to choose from in the small range. since even now i use a 600 watt inverter for my normal 300 watt load and 1500 watt for larger now and then loads. I also don't see inverter efficiency from 24 volts to 48 volts being much better than 24 volt. Is the only efficency/cost gain in the small wire? or what am i missing? im running all 2/0 from charge controllers to batteries and for battery connections as well as inverters..
                      So i'm not sure where i would gain going to 48 volts over 24 volts, as i probably will not grow this system past 2000 watts for my main system.

                      But even that is a unknown right now, because as bad as our electric company rips us off (no lie, there bad, states involved at this point) even my wife talks of going off grid completely,but winter is a beast. cleared 8 inches of snow from panels this morning. but over the last year its amazing how many rural homes in my area are now covered in panels,where as 2 years ago there were none. and i don't think many are feeding the grid as the "man" just slashed the credits for feeding the grid so here its not worth it in my view.

                      Comment


                      • #12
                        Originally posted by wrassie86 View Post
                        So far my water usage has been slight , I have been checking them the first of the month for the last 3 mos and only needed to add water last month and really the water was still well above the plates none needed the other day. i do have a hydrometer but it is crappy swing arm, will be ordering better glass one.
                        Good idea and decent hydrometers are cheap. You want one with Temperature Compensation. $10 or less. Use your hydrometer to determine SOC and what voltage to set your controller voltage too. Check Specific gravity toward the end of the day after the system has gone into Float Mode. If SPG is low, turn the voltage up. When the day comes your specific gravity spread is greater than .03 points from high to low is the time to EQ the batteries. Make sure you understand how, why, and when to do it. Do a search for OTC 4619 BATTERY HYDROMETER. Should be $10 or less if you shop around, or a DEKA/East Penn.

                        Originally posted by wrassie86 View Post
                        As i still think about the final voltage of 24 or 48 volt. I cant help but notice the inverter selection for 48 volts is slim/ pricey, most units are for really big power usage and not many to choose from in the small range.
                        Well you have discovered something and I can shine some more light on it for you. You are absolutely correct 48 volt Inverters are for larger systems. Here is a good rule of thumb to go by:

                        Up to 500 Watts / 12 Volt Battery
                        500 to 1500 watts / 24 Volt Battery
                        1500 to 4000 watts / 48 volt Battery.

                        Now here is the logic behind it and the key is Controllers Battery Capacity, and wiring expense. Generally speaking the largest controller you can get is 80 amps a a few 100 amp models. This might help you see the light and logic. Controller have a max wattage input vs battery voltage. For a 80 amp conmtroller the limits are roughly:

                        1000 watts @ 12 volts
                        2000 watts @ 24 volts
                        4000 watts @ 48 volts

                        So think of an extreme case here and say you want a 12 volt 2000 watt system. Well that would require two very expensive 80 and Controllers of about $600 each or $1200 dollar worth. It would also take some very large expensive wire, and most like force you to parallel batteries to get the capacity required to handle that much power.

                        But there are two more options. With a 24 volt system only requires one expensive 80 amp controllers, and smaller wire. However smart money would consider using 48 volts and a much less expensive 40 amp controller or maybe even a 60 amp model for future growth for up to 3000 watts.

                        You are right on the dividing line. With a 60 amp controller @ 24 volts you can go up to about 1500 watts, or 3000 watts @ 48 volts. So give that some thought. At least now you have some more info to make an informed decision.

                        One area you might of overlooked is how to configure the panels, and how you configure them is a big budget item. It also determines controller type. As you have noticed controller have a maximum INPUT VOLTAGE called Voc. For you want no less than 150 volts, and the higher the better as they go up to 600 volts. Yes you can charge a 12 volt battery with 500 volts. The higher the voltage, the more efficient the system and lower material cost. By code if you have more than 2 parallel strings (3 and up) requires you to use combiners and fuses which are expensive. Additionally lower voltages forrce you to use larger more expensive wire to overcome the losses incurred with lower voltages. The goal is to keep panel configuration to two parallel strings maximum. To do that requires a controller to handle the higher voltages. Unfortunately that option ship has sailed and you missed the boat.

                        Originally posted by wrassie86 View Post
                        But even that is a unknown right now, because as bad as our electric company rips us off (no lie, there bad, states involved at this point) even my wife talks of going off grid completely,but winter is a beast. cleared 8 inches of snow from panels this morning. but over the last year its amazing how many rural homes in my area are now covered in panels,where as 2 years ago there were none. and i don't think many are feeding the grid as the "man" just slashed the credits for feeding the grid so here its not worth it in my view.
                        No sir you do not want to do that. Do as you please, but rethink that. Time to wake you up. Anything you take off grid is going to cost you 5 to 10 times more for power the rest of your life, and that power off grid is very limited and you will be dark without power going off grid at times. Don't make that mistake, you will regret it as it will put a big hurt on your wallet replacing batteries every few years.

                        Hope that helps.
                        Last edited by Sunking; 03-04-2019, 08:52 PM.
                        MSEE, PE

                        Comment


                        • #13
                          2/0 from your charge controller? Definitely not necessary. I've never seen a charge controller that will take 2/0 cable. How is this 2/0 cable connected to the controller?
                          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                          Comment


                          • #14
                            Originally posted by littleharbor View Post
                            2/0 from your charge controller? Definitely not necessary. I've never seen a charge controller that will take 2/0 cable. How is this 2/0 cable connected to the controller?
                            Thanks for making me re check those, My tray cables are actually 4/0 largest the controller will except. 2/0 for batteries and inverter.

                            Comment


                            • #15
                              @ SunKing you are a wealth of info and while i digest all this info, of course you have lead me to more questions lol. One thing i'm well a where of is that the solar and battery storage is costing me more than grid and not very efficient ..... But the power, is mine , I'm making it and nobody can cut it off. Sometimes its about principle, even if it hurts the wallet a little more.

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