48 volt vs. 36 volt

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  • Jemplayer
    Member
    • Jun 2014
    • 77
    #1

    48 volt vs. 36 volt

    I am toying with the idea of getting a new inverter and changing my system from 48 to 36 v. The reason is I then only need to buy four more batteries to have two banks of 6, 6v 232ah batteries and don't need to add panels. I currently have 2400 watts in three string of 4 panels each string and one bank of eight 232ah 6v batts.

    Is this a good idea. Can I keep the wiring the same? And what is the advantage of one over the other. I know the 48 volt sys is better I just want to know how much better...as keeping it this way will cost a lot more. As will likely have too add another set of four panels for a total of 3200 watts and four more batteries.
    Tags: None
    • Sunking
      Solar Fanatic
      • Feb 2010
      • 23301
      #2
      48 volt is the right choice. 48 volt inverters are easy to find as it is a common voltage and will be less expensive watt for watt than 36 volt inverters and equipment. 48 volts is also more efficient and less expensive to operate and install.
      MSEE, PE

        Comment

        • Jemplayer
          Member
          • Jun 2014
          • 77
          #3
          Originally posted by Sunking
          48 volt is the right choice. 48 volt inverters are easy to find as it is a common voltage and will be less expensive watt for watt than 36 volt inverters and equipment. 48 volts is also more efficient and less expensive to operate and install.
          Do you think I have enough panels to charge two 232 ah banks. I would only be discharging to around 20% - 25% dod at most in summer and 15% odd in winter. Otherwise staying with 48 volts means more panels as well, and that gets more expensive..

            Comment

            • SunEagle
              Super Moderator
              • Oct 2012
              • 15123
              #4
              Originally posted by Jemplayer
              Do you think I have enough panels to charge two 232 ah banks. I would only be discharging to around 20% - 25% dod at most in summer and 15% odd in winter. Otherwise staying with 48 volts means more panels as well, and that gets more expensive..
              I'll let Sunking give you the final answer but based on a 2400 watt panel system at 48volts you can get up to 50amp of battery charging.

              So 2 banks of 8 x 6v 232Ah batteries gives you a 48volt 464AH system. 464AH / 50A = 9.28 hours which falls between the C/8 and C/12 charge rates of a FLA battery system. So IMO you would be ok.

              For that matter I am not sure how you got away with a 48volt 232Ah system with those 2400 watts of panels. That would see a C/4.6 rating (232Ah / 50A = 4.6 hr) which is very aggressive for FLA.

              Although I didn't see where you listed your Charge controller so I am assuming it is an MPPT type?

                Comment

                • Jemplayer
                  Member
                  • Jun 2014
                  • 77
                  #5
                  Originally posted by SunEagle
                  I'll let Sunking give you the final answer but based on a 2400 watt panel system at 48volts you can get up to 50amp of battery charging.

                  So 2 banks of 8 x 6v 232Ah batteries gives you a 48volt 464AH system. 464AH / 50A = 9.28 hours which falls between the C/8 and C/12 charge rates of a FLA battery system. So IMO you would be ok.

                  For that matter I am not sure how you got away with a 48volt 232Ah system with those 2400 watts of panels. That would see a C/4.6 rating (232Ah / 50A = 4.6 hr) which is very aggressive for FLA.

                  Although I didn't see where you listed your Charge controller so I am assuming it is an MPPT type?
                  Yes, I am well panelled for one bank. However, I have have only seen 50 amps a handful of times, then panels are making about 2700 watts at 84 volts.

                  Most of the time I see 32-38 amps, I mostly see around the 1800-2000 watts mark overall on sunny days. my panels face north east as to make use of early morning sun. it does peak at a little over 2000 watts for a while. But maybe there is more power there, as the mppt may not need all it can give.

                  I am using an mppt (60amp).

                    Comment

                    • SunEagle
                      Super Moderator
                      • Oct 2012
                      • 15123
                      #6
                      Originally posted by Jemplayer
                      Yes, I am well panelled for one bank. However, I have have only seen 50 amps a handful of times, then panels are making about 2700 watts at 84 volts.

                      Most of the time I see 32-38 amps, I mostly see around the 1800-2000 watts mark overall on sunny days. my panels face north east as to make use of early morning sun. it does peak at a little over 2000 watts for a while. But maybe there is more power there, as the mppt may not need all it can give.

                      I am using an mppt (60amp).
                      Ok. So you may rarely get that 50amps but even 32 - 38 amps is aggressive for a 232 Ah battery system.
                      Last edited by SunEagle; 10-28-2014, 10:53 AM. Reason: spelling

                        Comment

                        • Sunking
                          Solar Fanatic
                          • Feb 2010
                          • 23301
                          #7
                          Originally posted by Jemplayer
                          Do you think I have enough panels to charge two 232 ah banks. I would only be discharging to around 20% - 25% dod at most in summer and 15% odd in winter. Otherwise staying with 48 volts means more panels as well, and that gets more expensive..
                          With 2400 watts minimum battery requirement at 48 volts is 380 AH up to 600 AH so no problem as Suneagle pointed out. That puts you roughly at a C/10 charge current which is perfect. The reason you are not seing the amount of current you expect is most likely you have not discharged the batteries deep enough and the fact it is getting late in the year with the Sun sitting at lower angles in the southern sky.
                          MSEE, PE

                            Comment

                            • Sunking
                              Solar Fanatic
                              • Feb 2010
                              • 23301
                              #8
                              Originally posted by Jemplayer
                              Yes, I am well panelled for one bank. However, I have have only seen 50 amps a handful of times, then panels are making about 2700 watts at 84 volts.
                              Sure you got your numbers right? You have 2400 watts of panels right? MPPT controllers are in excess of 90% efficient. If 100 watts input you should be seeing in excess of 90 watts going out.
                              MSEE, PE

                                Comment

                                • SunEagle
                                  Super Moderator
                                  • Oct 2012
                                  • 15123
                                  #9
                                  Originally posted by Sunking
                                  With 2400 watts minimum battery requirement at 48 volts is 380 AH up to 600 AH so no problem as Suneagle pointed out. That puts you roughly at a C/10 charge current which is perfect. The reason you are not seing the amount of current you expect is most likely you have not discharged the batteries deep enough and the fact it is getting late in the year with the Sun sitting at lower angles in the southern sky.
                                  Actually he is in the Southern hemisphere (his panels face North East) and it should be getting toward Summer there so he might get even more out of those panels by December.

                                    Comment

                                    • Sunking
                                      Solar Fanatic
                                      • Feb 2010
                                      • 23301
                                      #10
                                      Originally posted by SunEagle
                                      Actually he is in the Southern hemisphere (his panels face North East) and it should be getting toward Summer there so he might get even more out of those panels by December.
                                      Oops did not catch that. Thanks for the corrections, my bad.

                                      Having said that my educated guess he is not discharging deep enough to remain in BULK charge mode long enough until high noon. Before high noon he has already switched to ABSORB and current tapers off in constant voltage charge modes. If that is the case he can test the theory. At high noon on a clear cloudless day turn on enough loads to turn the controller fully on and beyond and he should see expected current levels from the controller.
                                      MSEE, PE

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