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  • Off-grid system review

    We are developing a 2000 sq.ft. home at an off-grid location in Hawaii. Due to the fact that most of the solar systems in Hawaii are grid-tie, our solar subcontractor does not have a terrible amount of experience with 100% off-grid systems utilizing batteries and a generator. I would be grateful for a little input on your end:

    The system:

    30 SolarWorld SW 280 mono panels
    Outback GS 8048A inverter
    16 Rolls S550 batteries (20.5 Kwh)
    1 Generac 10kw generator

    The house will have electric appliances (range, oven, dish-washer, laundry and dryer). We recognize this is not ideal, but plan on using these appliances mostly during the day-time (we are located on the dry side of the island with heaps of sunshine) and staggered (not running everything at once). Nevertheless, we will still probably use about 10Kwh of juice at night (dish-washer, tv, lights, etc.).

    My main concern is the generator. I would like a system that supports the batteries anytime the load is at a certain level or if the batteries reach a certain point of depletion. Not sure if the Generac is ideal for this... Also, does the Outback GS 8048A include generator support? Or would we be better served with a different inverter.

    Your input is greatly appreciated.

  • #2
    From one of the sticky posts, it seems that the Outback inverter is not ideal for an off-grid system that needs gen support:

    "Both Schneider and Magnum Energy build programmable AGS that integrates with the system and will start a genset based on system loading. These controllers can can be used with three-wire or two-wire generators. Of the two, Schneider has 120/240V split-phase inverters (both XW and Conext SW series), Magnum Energy has a MSH4024RE 120V single-phase inverter available with generator support. They are both fairly simple to set up with three-wire gensets, or two-wire, and they are both proven to work.

    In older inverters, the Xantrex SW/SW Plus both have generator support, and are proven over many years to work flawlessly with all types of gensets using either the auto-start relays inside the SW, or the external GSM (Generator Start Module) used with the SW Plus.

    Outback does not build a programmable AGS that integrates with their systems. With an Outback all you have to auto-start a genset is a dry contact Aux port. Since the vast majority of generators used on off-grid power are three-wire, with an Outback you have to buy a pretty expensive Atkinson generator controller to convert three-wire generators to two-wire start."
    Having done a little more research, perhaps a pair of Schneider Conext XW+ 5548s would be the better choice...?

    And would it make sense to support the system with a pair of Honda EU3000iS generators?

    Comment


    • #3
      I'm assuming the battery bank is wired as 2 strings of 48V. It would be better if you bought large enough batteries for a single string.

      It also seems a little undersized in relation to the rest of the system. They would be @950Ah and the array can put out ~ 160A at 48V. That would give you a charge rate of C/5.9. That's on the high side and may void the warrantee. Charge rate should be between C/8 and C/12 with C/10 being about ideal.

      You also have the same problem with the inverter. It's capable discharge rate is higher than what the batteries are designed to support. It'll be worse with the 2 inverter setup.

      Without doing a load analysis i'd say you need to increase the battery bank size by about 50% to balance with the rest of the system and look at batteries that can be wired in a single string.

      WWW

      Comment


      • #4
        Thanks for the input, WWW. Forgive my ignorance, but what is the significance of having 1 string versus 2 or 3 strings?

        Comment


        • #5
          Originally posted by Cult of Dionysus View Post
          Thanks for the input, WWW. Forgive my ignorance, but what is the significance of having 1 string versus 2 or 3 strings?
          The difference is replacing the battery every two to three years instead of every 4 to 5 years assuming it was sized correctly to the load which you have not done.

          We can tell from what little information you have provided your whole system is completely out of acceptable tolerances. The most important peice of information missing is you do not mention how many watt hours you intend to use in a day. As it stands right now your batteries are sized to only support 9.2 Kwh per day, and your panels are sized to support 26 Kwh per day. Do you see any problem with that statement? It means you get to replace them in less than a year. You are going to fry your batteries with 160 amps of charge current. That is I assume you know a 8400 watt panel system requires two very expensive 80 amp MPPT charge controllers. The minimum size battery to support those panels are 1280 Amp Hours or Rolls S-1725 a 2 volt 1300 AH battery so you would need 24 of them.

          Having said all that is a moot point because you failed to do the very first requires step of determining your daily watt hour usage. Everything is determined by daily Watt Hour use and Location. At this point all anyone knows is location and a huge all electric home.
          MSEE, PE

          Comment


          • #6
            I'm double checking with Outback if the Radian GS8048A and Mate3 only support 2-wire gen start, like their FX series. If it hasn't changed to support 3-wire, you can use an Akinson GSCM to convert from 2-wire to 3-wire gen start. http://www.atkinsonelectronics.com/m.../gscm-mini.pdf . I'll confirm when I hear back from them.

            Schneider XW+ with AGS and Magnum MS-PAE4448 with ME-AGS-N both support 2- or 3-wire generators.
            Solar Queen
            altE Store

            Comment


            • #7
              OP: I sure hope you have not purchased anything yet or you can return some of that.

              Comment


              • #8
                Originally posted by Amy@altE View Post
                I'm double checking with Outback if the Radian GS8048A and Mate3 only support 2-wire gen start, like their FX series. If it hasn't changed to support 3-wire, you can use an Akinson GSCM to convert from 2-wire to 3-wire gen start. http://www.atkinsonelectronics.com/m.../gscm-mini.pdf . I'll confirm when I hear back from them.

                Schneider XW+ with AGS and Magnum MS-PAE4448 with ME-AGS-N both support 2- or 3-wire generators.
                Just got confirmation from Outback, you would need the Akinson GSCM to do 3-wire support. So if there are features in the Radian that you like, don't discount it because of the gen start, there's a solution for it.
                Solar Queen
                altE Store

                Comment


                • #9
                  Originally posted by mschulz View Post
                  OP: I sure hope you have not purchased anything yet or you can return some of that.
                  Nothing at all, luckily. My general contractor has fwd me the specs that his solar contractor has given (described in my initial post). Clearly he's put together something on paper which doesnt work. I'm trying to figure out what is a properly balanced system.

                  Based upon the input above, it seems that I need to upgrade the batteries, make sure the charge controllers are appropriate, and figure out the best inverter solution. Sunking, thanks for laying out some suggestions. That's very helpful, and my apologies for my ignorance.

                  One final point that I would appreciate a little input on... Assuming I get the batteries/controllers Sunking mentioned and either the Outback GS8048 or a pair of Schneiders, what would be a smart genet solution? Would a 10kw Generac make sense, one or two Hondas EUs, or something else?

                  Again, much of our energy use will be during the day, in one of the sunniest/dryest parts of Hawaii (350 days of sun). Probably 20-25Kwh during the day, if I'd have to throw a figure out there (including the 3hp water pump, appliances, etc.). At night, we won't use more than 5-10Kwh (led lights, tv, possibly one load of dishes).

                  Comment


                  • #10
                    Originally posted by Cult of Dionysus View Post
                    One final point that I would appreciate a little input on... Assuming I get the batteries/controllers Sunking mentioned and either the Outback GS8048 or a pair of Schneiders, what would be a smart genet solution? Would a 10kw Generac make sense, one or two Hondas EUs, or something else?
                    You need to start over and completely rethink things. If you rely on contractors, especially those selling you something is a really bad bad idea. I am a EE who works for my clients interest, not a vendor or industry. I can tell you right now going off-grid is a HORRIBLE ideal especially for you in an All Electric Home.

                    I know Hawaii electric rates are high. So is everything in Hawaii. Anything you take off grid or on battery is going to cost you 5 to 7 times more than buying it from the POCO even in Hawaii. Why do you want to do that? At this point you have no idea what you need. I suspect a 2000/ft2 home is going to require about 30 to 35 Kwh per day. In your location for off grid will require 10,000 watt panel (5 Sun Hours off season), three very expensive controllers, and a 11,000 pound $35,000 battery you get to replace every 5 to 7 years at even higher cost and that is mainland prices, not Hawaii. If I were a Solar Contractor would foam at the mouth to sell you that every 5 years as it would make me very rich man lining up pigeons like that. I advise you to reconsider. I won't charge you a dime.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      You need to start over and completely rethink things. If you rely on contractors, especially those selling you something is a really bad bad idea. I am a EE who works for my clients interest, not a vendor or industry. I can tell you right now going off-grid is a HORRIBLE ideal especially for you in an All Electric Home.

                      I know Hawaii electric rates are high. So is everything in Hawaii. Anything you take off grid or on battery is going to cost you 5 to 7 times more than buying it from the POCO even in Hawaii. Why do you want to do that? At this point you have no idea what you need. I suspect a 2000/ft2 home is going to require about 30 to 35 Kwh per day. In your location for off grid will require 10,000 watt panel (5 Sun Hours off season), three very expensive controllers, and a 11,000 pound $35,000 battery you get to replace every 5 to 7 years at even higher cost and that is mainland prices, not Hawaii. If I were a Solar Contractor would foam at the mouth to sell you that every 5 years as it would make me very rich man lining up pigeons like that. I advise you to reconsider. I won't charge you a dime.
                      The site is nearly ten miles from the nearest utilities.

                      Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.

                      Comment


                      • #12
                        Originally posted by Cult of Dionysus View Post
                        The site is nearly ten miles from the nearest utilities.

                        Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.
                        If you going to use the 2400AH Rolls batteries, then you need about 48 of those panels and three 80AMP Classic 150 charge controller and 15KVA Generator to charge those batteries properly.

                        Comment


                        • #13
                          Originally posted by Cult of Dionysus View Post
                          The site is nearly ten miles from the nearest utilities.

                          Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.
                          That is because I made a mistake. To supply you with 35 Kwh/day at 48 volts requires a 3600 AH battery or 175 Kwh capacity. Lead Acid batteries weigh in at 60 to 65-Lbs/Kwh and a good 5 to 7 year battery cost $ 200 to $240 per Kwh. So do the math for quick calculations 175 x 60 pounds weighs 10,500 pounds and cost $200 x 175 = $35000

                          No go find the actual product and the real numbers are 48 units of Rolls 2 OS 33 PS, 2 volt 1800 AH for a total of 3600 AH at 48 volts. Mainland cost are roughly $770 per unit x 48 = $36,960 and weigh 285 pounds wet x 48 = 13,680 pound. Sorry I was wrong, I was working on another project and transposed numbers. To generate 35 Kwh per day in your locations still requires 11,000 watt panel system and a 15 to 20 Kw generator.

                          Point here is you have no idea what you need. What you stated will not work. Once you have learned what it really takes, you may change course. I could care less what you do because I am not making or loosing a dime on you. What i do know is if you go forward is going to make someone a lot of money. If it were me designing would be cost plus 15%, or about $10 to $15K shuffling papers and numbers around. You contractors and suppliers will make quite a bit more.
                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by Sunking View Post
                            That is because I made a mistake. To supply you with 35 Kwh/day at 48 volts requires a 3600 AH battery or 175 Kwh capacity. Lead Acid batteries weigh in at 60 to 65-Lbs/Kwh and a good 5 to 7 year battery cost $ 200 to $240 per Kwh. So do the math for quick calculations 175 x 60 pounds weighs 10,500 pounds and cost $200 x 175 = $35000

                            No go find the actual product and the real numbers are 48 units of Rolls 2 OS 33 PS, 2 volt 1800 AH for a total of 3600 AH at 48 volts. Mainland cost are roughly $770 per unit x 48 = $36,960 and weigh 285 pounds wet x 48 = 13,680 pound. Sorry I was wrong, I was working on another project and transposed numbers. To generate 35 Kwh per day in your locations still requires 11,000 watt panel system and a 15 to 20 Kw generator.

                            Point here is you have no idea what you need. What you stated will not work. Once you have learned what it really takes, you may change course. I could care less what you do because I am not making or loosing a dime on you. What i do know is if you go forward is going to make someone a lot of money. If it were me designing would be cost plus 15%, or about $10 to $15K shuffling papers and numbers around. You contractors and suppliers will make quite a bit more.
                            Thanks, appreciate the input and clarifications. Will provide an update when the project is done.

                            Comment


                            • #15
                              Is propane an option?

                              Would it be possible to use propane instead of electric for the stove, dryer, and oven? Even better, a clothes line instead of a dryer? As I'm sure you know, anything that makes heat or cold use the most amount of power. The fact that you are using most of the power during the day doesn't help with an off grid system, you still have to put all of the power into the battery bank before you can use it, so you'll be beating up your batteries during the day.

                              I have tons of clients in the islands who have successfully gone off-grid, but you have to make concessions, you can't have it all without spending a large fortune.
                              Solar Queen
                              altE Store

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