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  • First grid tie system, advice is appreciated.

    My experience with solar has been with 4 panels 100w each going into a charge controller and battery bank.

    However, I got a quote from a family members client for panels at 70 cents a watt. Its 26 panels, 220w each, and the pallet is 26 units for a total of 5,720w rating.

    If I feed these into the grid I have a few questions.

    -Should these be wired parallel or in series, and what is the advantage of doing it that way?
    -What hardware is good-better-best for tying it into the grid?
    -Are there currently any legal practical ways to also feed and maintain some power into a battery bank for use if the grid goes down?
    -When wiring these, is the process just to take MC4 splitters and combine 2 panels at a time, then take each of those and combine again? What I see in my head is something that resembles the shape of a tournament bracket for a sports game, is this the correct concept?


    Any advice is much appreciated!

  • #2
    Originally posted by 308AndyJ View Post
    My experience with solar has been with 4 panels 100w each going into a charge controller and battery bank.

    However, I got a quote from a family members client for panels at 70 cents a watt. Its 26 panels, 220w each, and the pallet is 26 units for a total of 5,720w rating.

    If I feed these into the grid I have a few questions.

    -Should these be wired parallel or in series, and what is the advantage of doing it that way?
    -What hardware is good-better-best for tying it into the grid?
    -Are there currently any legal practical ways to also feed and maintain some power into a battery bank for use if the grid goes down?
    -When wiring these, is the process just to take MC4 splitters and combine 2 panels at a time, then take each of those and combine again? What I see in my head is something that resembles the shape of a tournament bracket for a sports game, is this the correct concept?


    Any advice is much appreciated!
    Welcome to Solar Panel Talk.

    There is a big difference between a small off grid battery system and a grid tie system. Before you concern yourself with how to wire the panels together you will need to understand what your local Electric Utility requires for a grid tie system. Next you will need to submit electrical and mechanical plans to get approval and a permit. Based on your questions you will also need to get a licensed electrician to do most of your electrical work including the connection to your power panel.

    A grid tie system is usually engineered to make sure the panels are mounted in the best orientation and properly wired to a grid tie inverter. This is not a project for someone that has little experience with electrical and while you may get some good feedback and suggestions here on the forum most people will tell you that installing a 5kw system is not easy and usually requires approvals from the Utility, City inspectors and maybe your home owners insurance company.

    I would suggest you do some research starting with the Utility requirements and local electrical codes.

    Comment


    • #3
      Originally posted by SunEagle View Post
      Welcome to Solar Panel Talk.

      There is a big difference between a small off grid battery system and a grid tie system. Before you concern yourself with how to wire the panels together you will need to understand what your local Electric Utility requires for a grid tie system. Next you will need to submit electrical and mechanical plans to get approval and a permit. Based on your questions you will also need to get a licensed electrician to do most of your electrical work including the connection to your power panel.

      A grid tie system is usually engineered to make sure the panels are mounted in the best orientation and properly wired to a grid tie inverter. This is not a project for someone that has little experience with electrical and while you may get some good feedback and suggestions here on the forum most people will tell you that installing a 5kw system is not easy and usually requires approvals from the Utility, City inspectors and maybe your home owners insurance company.

      I would suggest you do some research starting with the Utility requirements and local electrical codes.


      Thank you for the info!

      Based on the budget available, I would like to try to do the assembly myself. With careful examination, lots of research and time, and inspections from the proper authorities, I feel the safety risk is nullified, and the only thing I stand to lose is time doing something, then re-doing it in a more proper way.

      It appears most grid tie inverters of the 6,000w size take a range of volts, so in regards to parallel or series, I can chose which ever I please. Is there an advantage to 12v versus 24V, or 48V?

      Comment


      • #4
        Originally posted by 308AndyJ View Post
        Thank you for the info!

        Based on the budget available, I would like to try to do the assembly myself. With careful examination, lots of research and time, and inspections from the proper authorities, I feel the safety risk is nullified, and the only thing I stand to lose is time doing something, then re-doing it in a more proper way.

        It appears most grid tie inverters of the 6,000w size take a range of volts, so in regards to parallel or series, I can chose which ever I please. Is there an advantage to 12v versus 24V, or 48V?
        Grid tie inverters do not have voltage ratings of 12, 24 or 48. Those are plug in type inverters which are illegal in the US.

        What you will be looking for is similar to a Sunny Boy 6000tl which gets hardwired (by a licensed electrician) to your house main circuit breaker panel.

        Something like that can accept up to 6000 watts of panels with a maximum input voltage of 600dc so you can put a number of panels in series as long as they do not add up to 600 volts. The output voltage would be 240volt ac for most houses.

        A grid tie system is not simple so before you spend anything you really need to do more research as well as contacting your Electric Utility to find out what they allow and who can do the work.

        Comment


        • #5
          Originally posted by 308AndyJ View Post
          My experience with solar has been with 4 panels 100w each going into a charge controller and battery bank.

          However, I got a quote from a family members client for panels at 70 cents a watt. Its 26 panels, 220w each, and the pallet is 26 units for a total of 5,720w rating.

          If I feed these into the grid I have a few questions.

          -Should these be wired parallel or in series, and what is the advantage of doing it that way?
          -What hardware is good-better-best for tying it into the grid?
          -Are there currently any legal practical ways to also feed and maintain some power into a battery bank for use if the grid goes down?
          -When wiring these, is the process just to take MC4 splitters and combine 2 panels at a time, then take each of those and combine again? What I see in my head is something that resembles the shape of a tournament bracket for a sports game, is this the correct concept?


          Any advice is much appreciated!

          Series vs parallel.
          You want to wire as many as you practically can in series. Voltage is cheap, current is expensive. Voltage is accommodated with adding plastic, current is accommodated with adding metal. Voltage is also what enables you to have power travel long distances, and thus not need as much wire size to mitigate resistive losses.

          The industry norm, is for most equipment on the DC side to be rated for to withstand up to 600Vdc. You enter an entirely new set of rules, for circuits that are any higher in voltage. That is, the open circuit value adjusted for cold temperature, multiplied by modules in series. In your case, I recommend 2 source circuits of 13. Make sure that this is compatible with the voltage range of all other equipment involved on the DC side.


          Hardware for grid-tie.
          Any inverter that is listed as a utility-interactive inverter. In general, its nameplate power can be slightly lower than your panels' nameplate power. In your case, a 5 kW inverter should do, which is a very common size. It can connect to your grid at a dedicated 30A, 2-pole breaker. Locate it in a typical 200A household panel, opposite from the main supply.

          Battery-backup.
          You'll need an inverter, or a system of inverters that is specifically built to do this. SMA makes a Sunny Boy/Sunny Island system. The Sunny Boy series of inverters is for generic grid tied systems, and the Sunny Island system can be the grid-battery interface. You can buy the Sunny Boy now, and buy the Sunny Island years later, when you do decide to do batteries. The Sunny Island system will interface between your general loads panel, and your critical loads panel, that you separate, so that only the critical loads run, isolated from the grid, during outages. There are other manufacturers that do it all in one inverter unit, such as Outback.

          Grid-tied only inverters, must shut off when the utility is down. Any "three legged creature" inverter must be able to completely disconnect from the utility, while running on battery backup.


          Combining.
          You cannot combine more than two circuits, without using fuses. Two circuits get a special exception, because circuit 2 cannot overload circuit 1, under fault conditions of circuit 2. For 3 or more circuits, you need to use fuses for each string, and have a load-break rated disconnect immediately nearby.

          While it is acceptable by code to use MC4 splitters in buried deep in the array field, I do not recommend doing this. I recommend any point of circuit combination to be in a comfortable place to stand, that you can find easily and where you can see what you are doing. This is a point that you should test the voltage of each string, before connecting. And you should be able to service it easily in the future.

          Most string inverters have a set of fuses for combining (usually up to 4 or 6) source circuits at the inverter. You can travel with individual wiring back to the inverter, and land on the terminals available there. Or use the fuse-bypass terminal, if you combined in the field.


          "tournament bracket for a sports game"
          No, do not do this. If you are going to "bare tap" circuits together without fuses, STOP AT TWO. The #10 wire used with the MC4 connectors is only rated to handle the current of 2 typical circuits. Use a listed DC combiner, and upgrade the output wiring, if you need to do more than 2 circuits in parallel.


          When you parallel circuits, they need to all have identical panels in series, in identical numbers. Unless otherwise directed by inverter manuals, keep all panels the same on the same inverter.

          Comment


          • #6
            Originally posted by carultch View Post
            Series vs parallel.
            You want to wire as many as you practically can in series. Voltage is cheap, current is expensive. Voltage is accommodated with adding plastic, current is accommodated with adding metal. Voltage is also what enables you to have power travel long distances, and thus not need as much wire size to mitigate resistive losses.

            The industry norm, is for most equipment on the DC side to be rated for to withstand up to 600Vdc. You enter an entirely new set of rules, for circuits that are any higher in voltage. That is, the open circuit value adjusted for cold temperature, multiplied by modules in series. In your case, I recommend 2 source circuits of 13. Make sure that this is compatible with the voltage range of all other equipment involved on the DC side.


            Hardware for grid-tie.
            Any inverter that is listed as a utility-interactive inverter. In general, its nameplate power can be slightly lower than your panels' nameplate power. In your case, a 5 kW inverter should do, which is a very common size. It can connect to your grid at a dedicated 30A, 2-pole breaker. Locate it in a typical 200A household panel, opposite from the main supply.

            Battery-backup.
            You'll need an inverter, or a system of inverters that is specifically built to do this. SMA makes a Sunny Boy/Sunny Island system. The Sunny Boy series of inverters is for generic grid tied systems, and the Sunny Island system can be the grid-battery interface. You can buy the Sunny Boy now, and buy the Sunny Island years later, when you do decide to do batteries. The Sunny Island system will interface between your general loads panel, and your critical loads panel, that you separate, so that only the critical loads run, isolated from the grid, during outages. There are other manufacturers that do it all in one inverter unit, such as Outback.

            Grid-tied only inverters, must shut off when the utility is down. Any "three legged creature" inverter must be able to completely disconnect from the utility, while running on battery backup.


            Combining.
            You cannot combine more than two circuits, without using fuses. Two circuits get a special exception, because circuit 2 cannot overload circuit 1, under fault conditions of circuit 2. For 3 or more circuits, you need to use fuses for each string, and have a load-break rated disconnect immediately nearby.

            While it is acceptable by code to use MC4 splitters in buried deep in the array field, I do not recommend doing this. I recommend any point of circuit combination to be in a comfortable place to stand, that you can find easily and where you can see what you are doing. This is a point that you should test the voltage of each string, before connecting. And you should be able to service it easily in the future.

            Most string inverters have a set of fuses for combining (usually up to 4 or 6) source circuits at the inverter. You can travel with individual wiring back to the inverter, and land on the terminals available there. Or use the fuse-bypass terminal, if you combined in the field.


            "tournament bracket for a sports game"
            No, do not do this. If you are going to "bare tap" circuits together without fuses, STOP AT TWO. The #10 wire used with the MC4 connectors is only rated to handle the current of 2 typical circuits. Use a listed DC combiner, and upgrade the output wiring, if you need to do more than 2 circuits in parallel.


            When you parallel circuits, they need to all have identical panels in series, in identical numbers. Unless otherwise directed by inverter manuals, keep all panels the same on the same inverter.


            Stellar information, Thank you SO very much!

            Comment


            • #7
              Originally posted by carultch View Post
              Series vs parallel.
              You want to wire as many as you practically can in series. Voltage is cheap, current is expensive. Voltage is accommodated with adding plastic, current is accommodated with adding metal. Voltage is also what enables you to have power travel long distances, and thus not need as much wire size to mitigate resistive losses.

              The industry norm, is for most equipment on the DC side to be rated for to withstand up to 600Vdc. You enter an entirely new set of rules, for circuits that are any higher in voltage. That is, the open circuit value adjusted for cold temperature, multiplied by modules in series. In your case, I recommend 2 source circuits of 13. Make sure that this is compatible with the voltage range of all other equipment involved on the DC side.


              Hardware for grid-tie.
              Any inverter that is listed as a utility-interactive inverter. In general, its nameplate power can be slightly lower than your panels' nameplate power. In your case, a 5 kW inverter should do, which is a very common size. It can connect to your grid at a dedicated 30A, 2-pole breaker. Locate it in a typical 200A household panel, opposite from the main supply.

              Battery-backup.
              You'll need an inverter, or a system of inverters that is specifically built to do this. SMA makes a Sunny Boy/Sunny Island system. The Sunny Boy series of inverters is for generic grid tied systems, and the Sunny Island system can be the grid-battery interface. You can buy the Sunny Boy now, and buy the Sunny Island years later, when you do decide to do batteries. The Sunny Island system will interface between your general loads panel, and your critical loads panel, that you separate, so that only the critical loads run, isolated from the grid, during outages. There are other manufacturers that do it all in one inverter unit, such as Outback.

              Grid-tied only inverters, must shut off when the utility is down. Any "three legged creature" inverter must be able to completely disconnect from the utility, while running on battery backup.


              Combining.
              You cannot combine more than two circuits, without using fuses. Two circuits get a special exception, because circuit 2 cannot overload circuit 1, under fault conditions of circuit 2. For 3 or more circuits, you need to use fuses for each string, and have a load-break rated disconnect immediately nearby.

              While it is acceptable by code to use MC4 splitters in buried deep in the array field, I do not recommend doing this. I recommend any point of circuit combination to be in a comfortable place to stand, that you can find easily and where you can see what you are doing. This is a point that you should test the voltage of each string, before connecting. And you should be able to service it easily in the future.

              Most string inverters have a set of fuses for combining (usually up to 4 or 6) source circuits at the inverter. You can travel with individual wiring back to the inverter, and land on the terminals available there. Or use the fuse-bypass terminal, if you combined in the field.


              "tournament bracket for a sports game"
              No, do not do this. If you are going to "bare tap" circuits together without fuses, STOP AT TWO. The #10 wire used with the MC4 connectors is only rated to handle the current of 2 typical circuits. Use a listed DC combiner, and upgrade the output wiring, if you need to do more than 2 circuits in parallel.


              When you parallel circuits, they need to all have identical panels in series, in identical numbers. Unless otherwise directed by inverter manuals, keep all panels the same on the same inverter.


              Help me just a bit further with wrapping my head around this.

              Lets say I use 24 panels rated at 12v each. Would the best way be:

              Wire in series, six sets of 4 panels. Each set of 4 would then have a 48V rating, and there would be 6 of these sets which would be in parallel.

              or are you suggesting

              Wire in series two sets of 12 panels. Each set would be 144v and there would be 2 of these sets to then parallel.

              What I am referring to as sets, is that what a "circuit" is that you reference?

              Comment


              • #8
                Originally posted by 308AndyJ View Post
                Help me just a bit further with wrapping my head around this.

                Lets say I use 24 panels rated at 12v each. Would the best way be:

                Wire in series, six sets of 4 panels. Each set of 4 would then have a 48V rating, and there would be 6 of these sets which would be in parallel.

                or are you suggesting

                Wire in series two sets of 12 panels. Each set would be 144v and there would be 2 of these sets to then parallel.

                What I am referring to as sets, is that what a "circuit" is that you reference?
                A panel "rated at" 12 volts will typically have an output Vmp of 18V and a Voc of 22-23 volts. It will also not be the most economical way to get watts of panels for either a grid tie inverter or an MPPT Charge Controller for batteries.
                Many grid tie inverters can handle DC input in the 400-600V range. For one of those you can put as many as 20 "12V" panels in series in one string, although that may not be the most efficient way to go.
                I think that you are still not clear on whether you are looking toward a pure grid tie installation or a hybrid system or two separate systems, grid tie and off-grid (with batteries). You cannot have the same set of panels connected simultaneously to the input of a GTI and a CC.
                Unless you have frequent long power failures, a hybrid or off grid system will cost you a lot more and be harder to maintain than a good generator.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #9
                  Originally posted by inetdog View Post
                  A panel "rated at" 12 volts will typically have an output Vmp of 18V and a Voc of 22-23 volts. It will also not be the most economical way to get watts of panels for either a grid tie inverter or an MPPT Charge Controller for batteries.
                  Many grid tie inverters can handle DC input in the 400-600V range. For one of those you can put as many as 20 "12V" panels in series in one string, although that may not be the most efficient way to go.
                  I think that you are still not clear on whether you are looking toward a pure grid tie installation or a hybrid system or two separate systems, grid tie and off-grid (with batteries). You cannot have the same set of panels connected simultaneously to the input of a GTI and a CC.
                  Unless you have frequent long power failures, a hybrid or off grid system will cost you a lot more and be harder to maintain than a good generator.
                  Thank you,

                  Edit: Taking SunEagle's advice. Going with 2 circuits of 13 panels in series. After taking the 2 groups of 13 and wiring each group together in series, I'll have 2 negative and 2 positive leads. Do I then connect them in parallel to get 1 pos and 1 neg lead which goes into the grid tie inverter? Is this what SunEagle was referring to with MC4 cables being sufficient for this job, or do I need other hardware to make this parallel connection?

                  Comment

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