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  • Battery Recommendation - New System

    I am trying to put together an off-grid system and I need some guidance regarding appropriate battery selection. I already have a Xantrex 6 kW inverter and Outback CC. I also have twelve (12) 280 watt low grade panels (Chinese) which I plan to configure in 4 arrays of 3 panels each.
    I am targeting delivery of 7 to 10 KVA daily from the system – Btw I am in Jamaica.
    So can you recommend what AH capacity battery string I will need to acquire as well as choice of brand (I see local vendors offering the Trojan, DEKA, Rolls, Trojan, US Power and Trace batteries). From reviewing other material on this site I already realize the need for FLA type battery but can someone help me with indicating specific battery models as well as any accessories that will help to ensure my system works well. I seem mention of a TriMetric device but not sure if this is required.

  • #2
    What voltage is the system? Only correct answer is 48 volts. Otherwise start over.

    You do not really have enough panel wattage to run a 6 Kw inverter, 3 Kw is as large as you can realistically go without wasting a lot of power on an over sized inverter, and battery. But if you had a 5 to 6 Kw panel array it would require a 48 volt 1000 AH 2800 pound battery. Problem is to support a 48 volt 1000 AH battery requires a minimum 5000 watt panel.

    You kind of have things mixed up. If you need 7 Kwh per day requires a 48 volt 750 AH battery. A 750 AH battery in Jamaica needs a 3750 watt panel, 80 amp MPPT controller and an inverter no larger than panel wattage or in this case up to 4000 but only if you need it. Inverters should be as small as possible to conserve power.
    MSEE, PE

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    • #3
      Sunking - Yes the system is 48 volts. I do have short term plans to purchase another 6 panels (280W each). The Outback CC is 80 amp MPPT.

      Comment


      • #4
        FLA batteries have rather high internal resistance, which limits how much current they can provide without excessive voltage sag. For FLA batteries max load you can put on them without going over 2 to 3 % voltage sage is C/8 where C = the battery rated AH capacity. So to supply 93 amps the battery capacity needs to be a minimum of 8 x 93 amps = 744 AH. Understand so far?

        On the charge side of the battery it needs to be between C/8 and C/12 with C/10 being perfect for a charge current. Again C = the battery AH capacity. So the highest current of C/8 is the exact same 93 amps. On the low end of C/12 on a 744 AH battery is = 63 amps. 74 amps is C/10 and ideal charge rate. So what panel wattage does it take to generate 63 to 93 amps on a MPPT controller? Answer is anywhere from 3150 watts up to 4650 watts. At C/10 = 3700 watts.

        OK time to put the connection together. Panel Wattage roughly equal inverter wattage.

        OK Mon you are in Jamaica my favorite vacation hide-away and you have excellent solar Insolation of roughly 5.5 sun hours. That means you can run around C/12 charge current which is a good thing. So now work out the details based on on your daily Kwh usage. To get 7 Kwh per day you need a 48 volt battery with a minimum capacity of 700 AH battery. In fact your solar insolation is a little too good. To generate 7 Kwh of usable energy per day only requires 1900 watts. Problem is to get a minimum charge current of C/12 or 58 amps requires a minimum panel wattage of 2900 watts. It can be as high as 4375 watts for C/8.

        Hope that helps.
        MSEE, PE

        Comment


        • #5
          Hi Sunking I got it so far; fully understood. So I just need to ensure I have sufficient panels to meet the range between 2900 and 4375 watts. I already have 3360 watts from the 12 x 280 panels and I plan to acquire additional panels.
          Additionally, I need to acquire 700 AH capacity batteries. The Rolls is just not affordable for me at this time; but I see what appears to be a good deal in Jamaica on Trojan L16 batteries (370 AH). I know multiple parallel strings are not the ideal config but what do you think about using 2 strings of Trojan L16 to provide 740 AH capacity battery bank. If this is OK let me know of any recommended safeguards to make this work successfully.

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          • #6
            Originally posted by watsonson View Post
            Hi Sunking I got it so far; fully understood. So I just need to ensure I have sufficient panels to meet the range between 2900 and 4375 watts. I already have 3360 watts from the 12 x 280 panels and I plan to acquire additional panels.
            Additionally, I need to acquire 700 AH capacity batteries. The Rolls is just not affordable for me at this time; but I see what appears to be a good deal in Jamaica on Trojan L16 batteries (370 AH). I know multiple parallel strings are not the ideal config but what do you think about using 2 strings of Trojan L16 to provide 740 AH capacity battery bank. If this is OK let me know of any recommended safeguards to make this work successfully.
            Yeah it will work, just try not to go more than 2 strings. Wire them on the diagonal and you should be OK.
            MSEE, PE

            Comment


            • #7
              Mr. Watson,
              Where are you in Jamaica? if you are not in Mandeville you will be ok with the amount panels you have to get 7 to 10 KWH.

              What you should not do is to tell off JPS. keep them for rainy days, and try put the heavy load on sun hours. We start to get current as early as 6:30 in the morning and as late as 5:30 just that on those hours we only get a faction of the rated power.

              You can start with 8 of those Trojan L16 batteries first with your 12 panels. with load in the day your charge current will be in the low end. you will get about 40 to 60 amps at about 55 volt, take away 20 amps for the load you will end up 30 to 40 amps for charging.

              Comment


              • #8
                Hi Paul. I am in the Spanish Town area. I see where a local vendor is selling then Trojan L16-RE batteries for J$35k each. I want to go completely off-grid and as you suggest keep JPSCo as back-up only. Typically my monthly bill shows a consumption in the region of 350 Kwh. So I want to determine whether 1 string or 2 strings of the L16 batteries will be adequate.
                Do you still recommend I start with just 1 string; that would be very good news for my budget.

                Comment


                • #9
                  If you can use your heavy load in the day time when the sun is shinning, you can use one string. We start get power from the sun from 7 am. or 8 am in winter time. power still come from the sun around 4:30 pm to 5 pm. you may have 15 hours depend on the battery bank. the load is 486 watts if it divided evenly. but you will use less when you go sleep. So let us say 400 watts for 15 hours that is 6000 watts and at 48 volts it is 125 AHS. that is about 33.5% DOD, I think that would be better than buy two bank of batteries and have to increase panels capacity and the charge controller too.

                  Stick with one bank and save the money for the next bank around 5 to 8 years later. Just remember any time you got rain you turn on JPS to charge back the battery. That is what I do. I use 600 to 700 KWH a month, that is about 20 to 24 KWH per day. I have 6400 watts panels and two strings batteries, one is 350 amps hours and the other one is 400 amps hours. I have to use generator or JPS any day I got heavy over cast or rain. I live in Mandeville. the worst parish for solar energy.

                  Hope this will help.

                  Cherrs

                  Comment


                  • #10
                    OK great. I do appreciate this guidance because I wanted to make sure I wasn't missing anything.
                    So the great news is that I should be able to survive with a single string of L16s. However I need you to clarify the charging set-up when it rains. I am figuring that if it starts raining during the day I should simply switch to commercial power until next day. The way I have wired my system - when solar power is in use the main breaker to JPS is switched off; there is no JPS connection to my Xantrex inverter so no way of JPS charging the batteries.
                    Let me know what I am missing. Also, do I need any special battery monitor to track state of charge or just follow the analog current meter I will be setting up to monitor basic charge/discharge status.

                    Comment


                    • #11
                      Originally posted by watsonson View Post
                      .... I already have a Xantrex 6 kW inverter and Outback CC....
                      What model of Xantrex ? Some have an internal charger that runs off the grid or generator. The internal charger, when programed properly, will recharge the batteries just fine from the grid. For most of the xantrex gear, you need a Combox or SCP to program it, same with some outback stuff, it may need a programmer (MATE?) to set it up properly.
                      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


                      • #12
                        Originally posted by watsonson View Post
                        OK great. I do appreciate this guidance because I wanted to make sure I wasn't missing anything.
                        So the great news is that I should be able to survive with a single string of L16s. However I need you to clarify the charging set-up when it rains. I am figuring that if it starts raining during the day I should simply switch to commercial power until next day. The way I have wired my system - when solar power is in use the main breaker to JPS is switched off; there is no JPS connection to my Xantrex inverter so no way of JPS charging the batteries.
                        Let me know what I am missing. Also, do I need any special battery monitor to track state of charge or just follow the analog current meter I will be setting up to monitor basic charge/discharge status.
                        You need to connect the XW6048 to the commercial power(JPSco). IT NEED to charge the battery bank periodically for equalization charge like once per month or at least twice per year, even the sun is shinning most of the time. You can put a breaker between the JPS line and the inverter so it keep off most of the time. I don't know Spanish town, but in Mandeville I have to use JPS to charge the battery quite often especially in winter months like this week.

                        You need to get some one program the XW6048, it is a very good inverter but you have to program it properly.

                        Comment


                        • #13
                          Originally posted by Mike90250 View Post
                          What model of Xantrex ? Some have an internal charger that runs off the grid or generator. The internal charger, when programed properly, will recharge the batteries just fine from the grid. For most of the xantrex gear, you need a Combox or SCP to program it, same with some outback stuff, it may need a programmer (MATE?) to set it up properly.
                          Mike, in Jamaica most of the 6000watts Xantrex inverter is the XW6048. most dealer recommended that model.

                          Comment


                          • #14
                            Li-ion Are good too but Cost 2x to 3x what PD cost

                            I would go with Li-ion if i had the money they last longer and can get more out them ( the voltage stays higher longer the PD) there liter weight , but cost a lot more and u should a BMS on them too..

                            Comment


                            • #15
                              Guys - Paul is correct I have the XW6048 inverter. But I am reluctant to make any connection from the commercial power source (JPS) to my inverter simply because the power company is notorious for zapping customer equipment and they would not compensate me if they damaged my inverter. So I really would prefer to completely avoid connecting the grid to my inverter even for use in occasional equalize charging. I can't see why the panels via my Outback CC (MPPT) can't provide whatever equalize charge that is required occasionally.
                              Btw - do I need to have BMS with the L16s. I just went to but 8 of these batteries today.

                              Comment

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