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  • Help with off-grid solar circuit

    G’day fellas,

    I’ve been drawing up a circuit in my iPhone notes for the solar circuit I want to put in the house I am going to build. I have only put together an off-grid solar system once before for my parents’ house, but it was much smaller. My parents’ house has a 3000w array with a 100v/50a MPPT, a 3000w inverter, and 8 6v 232ah deep-cycle lead acid batteries. As to the brands and other details I cannot remember because I put the system in years ago. I’m not an electrician or anything, I have worked in construction and now work in another field. Basically, I am just saying that I don’t proclaim to be an expert.

    Anyways, as I will be running AC and dryers and the such in my house, the system is a fair bit bulkier and I reckoned I could use more sets of eyes on my idea. The PV array consists of 32 24v 300w Renogy panels off Amazon (or somewhere else if I can find cheaper) with VOC 38.92. So my system will be 9,600w which should give us a little over what we truly need but allow me to run power tools and such in my workshop without worry. These will be wired as eight sets of four panels in series. So each set would be at max about 156v, and 12.5a. These will then go down to some DC disconnect switches rated for 16a because I can’t find any rated at 13a on Amazon. From there I’m ganna run the wires down still as eight sets of four into 16a breakers. They are 16a for the same reason as the dc disconnect switches.

    After that, I’ll either solder or crimp all the negatives together and then all the positives together in parallel with now a max of about 156v and 100a. These two wires will then run into a 250v/100a MPPT. That will probably be a Victron because that’s what I used previously and they seem to be high quality. From here I’ll run the negative and positive through a 3-way fuse box with 100a fuses on each. From here the wires will go to 12 2v 1255ah Trojan carbon deep cycle batteries wires in series. This will give me 24v, and cause me to buy a slightly more expensive inverted because I was ganna originally use Wagan’s 10,000w inverter on Amazon but it is 12v. I didn’t wanna run the batteries as two 12v strings because I have read on the forum that this may cause two of the batteries to wear out quicker because obviously the charge controller goes off the battery “cell’s” overall voltage.

    Anyways, I’ll then run another short lead from the battery side of the fuse block from the positive to a 400a fuse in the middle. From here I’ll run a positive lead from this 400a fuse to the inverter, and another negative lead from the fuse box at the same terminal as the 100a fuse to the inverter. The inverter I am thinking is Sigineer 48v 10,000w inverter. I think it either runs or will run as 24v though. Not sure though, if it is 48v will it run fine with the 24v battery cell? Anyways, I calculated that with about 2.3 hours of full sun I should be able to get the batteries from 75% to 100%, and this is right where I want it for where we live.

    Also, I’ll be running grounds from the PV disconnects, breakers, MPPT, and inverter. I can’t remember the precise angle I need on panels but I think it was about 36 degrees for us. I’ll face the panels North, and they’ll be fixed because I don’t wanna do maintenance on a rotating array. The whole system will be on the ground, and the batteries/charge controller/inverter/etc will be stored in a shed right behind the panels. The shed will be well insulated. I was ganna set the batteries just on the concrete slab... I assume that is fine?

    Let me know your thoughts, and I appreciate you guys having a look! I’m just planning everything now, nothing is bought so plans are very flexible.

    I’ll be putting it all together myself so the cost is just materials, which should run me about $20k all up.

    Take care,

    Superdoom

  • #2
    Whoa.

    There are far better places to buy the high power gear, other than Amazon.

    150V is the death voltage for many charge controllers. Designing a system with a higher Array voltage, will instantly push you towards much more expensive controllers.
    The only mid size one that comes to mind is the Magnum PT-100, and then you get into the 600V charge controllers. For a 10kw system. maybe that's what you need anyway.
    Schneider has a good series of 48V. high power 240VAC inverters, Fuses, in the sizes you need, are best served by circuit breakers, for the best reliability.

    Read some of the off grid section stickies and plan your system very completly before you invest in any gear. Know your micorclimate, where the fog usually is, where the clouds roll in from....
    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
      Thanks for the reply, Mike!

      Hah! I feel ya, I just like how I can kinda do a one stop shop kinda deal. Plus I just recently moved so I don’t know of any local stores but if you have some online stores I should check out let me know!

      death voltage?? Man, that doesn’t sound good. Could you explain that more to me?

      So your advice would be to up the v and upgrade the MPPT?

      Looking into Schneider now, thank you for the recommendation. Do you reckon the 24v battery “cell” will workout okay with a 48v inverter?

      Breakers, got it. Is that just because fuses are one-time use and are a pain to replace in that rating? I always thought fuses were the most reliable because of their simplicity?

      Thank you, and I’m all over it.

      Comment


      • #4
        Righto, I just did some digging on the site about the low v thing, and I understand where you’re coming from now. So unrelated, I just found some cheaper panels but anyways, they are 24v 240w and 37.62 VOC I think. So I could run 40 of them for 9,600w total from four sets of 10, giving me a overall system with almost 380v and 50a. This seems better, because I don’t think I’m going to need all those amps anyways and the v seem better? Or should I go higher in v?

        Comment


        • #5
          Better get a brief edumacation about solar off grid, voltage vs amps,

          With a 10kw PV array (you are very close to that) you will use a 48V battery bank. 24V battery will double the number of charge controllers you will need

          Death voltage = MPPT controllers are rated for a certain Max Input voltage and max output amps. An internal logger circuit records the max input voltage for warranty denial.

          10kw @ 48V = 208A.. That would take 2 PT-100's, or 3ea 60A rated controllers Double those numbers for a 24V battery, 416A coming out of the controllers.
          Granted, that's only under really low battery at solar noon.

          MPPT controllers work by converting excess PV voltage, to battery amps. They are Watts In = Watts Out devices (with about 2% loss) PWM controllers are much less expensive and less complicated, they let the panels charge at panel amps & voltage, directly into the battery, requiring much larger cables to carry the higher amps from the PV to the controller.
          MPPT you run panels in series, with only 6 or so amps, using 12ga wire.

          There's lot's to learn before you start buying, and many reputable solar gear dealers. The big stuff is easy, but it's the little bits, like spare connectors for the 1 that breaks.......
          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


          • #6
            Thanks again for the reply, Mike.

            So I understand the basics of amps and voltage, and how they differ. I also have a primitive understanding of why more volts might be beneficial to charging the batteries. But I am still looking into this death voltage thing. Victron sells MPPT’s rated for up to 400v VDC, and their 250/100 controller is rated for 250v VDC. So I reckon the MPPT should be okay? Though I might do for their Skylla-TG instead and up the v to help charge the batteries?? That making sense?

            Just to help me out here, where is the 10,000w @ 48v coming into play here? In my original design I have 156v and 100a, and in the newer design I could have 380v and 50a. Also, the batteries would be 24v... or are you suggesting I up the battery voltage up to 48v?

            Yup, thank you for clarifying. I definitely understand the need for larger gauge wire for higher current. Depending on the design I will design my wires to be rated to take the current +25% so they aren’t a fire hazard and the fuses or breakers can do their job.

            Thank you, and I have started shopping around and already have knocked my total down to $16k for the job so I am happy about that.

            Comment


            • #7
              Oh, I see. You think I should just run a 48v solar array down to a PWN which chargers a 48v battery bank? I like the simplicity of that design, but I reckon after the loss of volts from power the charger, it might not be viable for a 48v PV array to charge a 48v battery bank.

              Again, I’m not an expert, I just try to read a lot of the forum.

              Comment


              • #8
                Your planned array 9600w, is close to 10kw for rough numbers. 10kw at the array, goes through the controller and you have 10kw coming out to the batteries (if sunny)

                MPPT lets you leverage the array voltage vs amps. You will have at least 2 or maybe up to 4, different strings from the PV to the controller.

                You are far, far, into the 48V battery. 24V will have dangerous amounts of amps and heavy, expensive, stiff copper wire. (it's the poor connections that are dangerous)

                Continue with research. I'm not familiar with some of the gear you mention, but the 1 page data sheet should show you all the info you need,
                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


                • #9
                  Gotcha buddy, thank you for your help. I’ll keep looking into it all.

                  Quick question for anyone, the fuse/breaker between the inverter and the batteries should be rated for the total array watts divided by the battery “cell” voltage, right?

                  So in my initial example it is 9,600/24 = 400a

                  Comment


                  • #10
                    Originally posted by Superdoom View Post
                    .....Quick question for anyone, the fuse/breaker between the inverter and the batteries should be rated for the total array watts divided by the battery “cell” voltage, right?

                    So in my initial example it is 9,600/24 = 400a
                    The wire size should be rated for the Amperage it may carry. The breaker should be based on wire size to protect the wire. Maybe that is what you meant.

                    Comment


                    • #11
                      Originally posted by Ampster View Post
                      The wire size should be rated for the Amperage it may carry. The breaker should be based on wire size to protect the wire. Maybe that is what you meant.
                      Hey, Ampster.

                      Yes, that is what I am trying to say, but I am trying to figure out how many amps the wire from the battery to the inverter will carry. Is there a way to figure that out?

                      Comment


                      • #12
                        Originally posted by Superdoom View Post

                        Hey, Ampster.

                        Yes, that is what I am trying to say, but I am trying to figure out how many amps the wire from the battery to the inverter will carry. Is there a way to figure that out?
                        It depends on the load on the inverter. From earlier posts you were talking about a 9600 Watt inverter. The Amperage of that at 48 volts would be 200 Amps and at 24 volts it would be 400 Amps. You can look up on a wire table to see what size wire to use to carry that load. Whatever wire size you ultimately use your fuse or breaker should be sized to protect the wire. That means the breaker or fuse should not be larger than the Amperage capacity of the wire.

                        Comment


                        • #13
                          Originally posted by Ampster View Post

                          It depends on the load on the inverter. From earlier posts you were talking about a 9600 Watt inverter. The Amperage of that at 48 volts would be 200 Amps and at 24 volts it would be 400 Amps. You can look up on a wire table to see what size wire to use to carry that load. Whatever wire size you ultimately use your fuse or breaker should be sized to protect the wire. That means the breaker or fuse should not be larger than the Amperage capacity of the wire.
                          Word up, so I was accurate. That makes me glad, because I did state that in my original post. Also, I was thinking of using fuses/breakers rated at the right amps, like 400a for the example above, but the wires to be rated at 25% above. So in that example, it would be wire rated for 500a. Is that necessary or not? I just saw in another post where someone mention this would make it more likely for the fuse to blow before the wires could catch fire.

                          Thanks for your help!

                          Comment


                          • #14
                            Originally posted by Superdoom View Post
                            .........Also, I was thinking of using fuses/breakers rated at the right amps, like 400a for the example above, but the wires to be rated at 25% above. So in that example, it would be wire rated for 500a. Is that necessary or not? I just saw in another post where someone mention this would make it more likely for the fuse to blow before the wires could catch fire.
                            You can always use a smaller breaker/fuse. Some people use heavier wire to reduce resistance if there are long runs. The likeliehood of the fuse to blow is more related to the likelihood of the load exceeding the fuse rating. In your case with a 9600 Watt Inverter what do you think the maximum load you are going to put on that? Have you found a resource for wire rated at 500 Amps and priced that? At some point copper or aluminum buss bars are going to more practical than wire for those kind of Amps. Also one needs to look at the ability of the batteries to provide that amount of power.
                            Last edited by Ampster; 03-27-2020, 12:28 PM.

                            Comment


                            • #15
                              [QUOTE=Ampster;n413002]
                              Originally posted by Superdoom View Post
                              .........Also, I was thinking of using fuses/breakers rated at the right amps, like 400a for the example above, but the wires to be rated at 25% above. So in that example, it would be wire rated for 500a. Is that necessary or not? I just saw in another post where someone mention this would make it more likely for the fuse to blow before the wires could catch fire.
                              /QUOTE]

                              You can always use a smaller breaker/fuse. Some people use heavier wire to reduce resistance if there are long runs. The likeliehood of the fuse to blow is more related to the likelihood of the load exceeding the fuse rating. In your case with a 9600 Watt Inverter what do you think the maximum load you are going to put on that? Have you found a resource for wire rated at 500 Amps and priced that? At some point copper or aluminum buss bars are going to more practical than wire for those kind of Amps. Also one needs to look at the ability of the batteries to provide that amount of power.
                              Righto. I would be pulling 9,000w at times, not for extended periods but just when I am running power tools in the shed.

                              That is a great question

                              Comment

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