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  • Flooded, VRLA or AGM

    In an off grid solar system in a tropical/desert like climate which deep cycle battery is best, flooded or Gel and if Gel, Puregel VRLA or AGM and why?

  • #2
    First eliminate gel as it it is too sensitive and fragile for cycled service. It cannot tolerate the high recharge rates required by solar. The gel dries out from rapid charging and the damage is permanent and accumulative. Second point there are two types of Lead Acid Battery. One being Flooded Lead Acid and the other is VRLA. In the VRLA family is two sub groups of AGM and Gel and we already eliminated Gel.

    Now to answer your question. Flooded should always be the first choice for many reasons. They cost less and last longer period, and that is all you really need to know.

    AGM is more of a niche application well suited for mobile applications like RV's, Trailers, and air planes where spills cannot be tolerated, and weight is an important factor. Also in extreme cold climates of -40 F and below because AGM will not freeze. Note fully charged FLA is good to -60 F. Another niche application is where one needs very high Charge and Discharge rates. Example in a place like Seattle WS where in winter they have less than 2 Sun Hours for much of the winter, and panel wattage's must be very high to recharge in a day which would give FLA battery problems. So before you consider AGM, consider is it worth the expense. AGM cost roughly twice as much as FLA for a given capacity, and last roughly half as long which means the long term cost of using AGM is 3 to 4 times more than FLA which is significant and a game changer once you are in the know.
    MSEE, PE

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    • #3
      Originally posted by Sunking View Post
      First eliminate gel as it it is too sensitive and fragile for cycled service. It cannot tolerate the high recharge rates required by solar. The gel dries out from rapid charging and the damage is permanent and accumulative. Second point there are two types of Lead Acid Battery. One being Flooded Lead Acid and the other is VRLA. In the VRLA family is two sub groups of AGM and Gel and we already eliminated Gel.

      Now to answer your question. Flooded should always be the first choice for many reasons. They cost less and last longer period, and that is all you really need to know.

      AGM is more of a niche application well suited for mobile applications like RV's, Trailers, and air planes where spills cannot be tolerated, and weight is an important factor. Also in extreme cold climates of -40 F and below because AGM will not freeze. Note fully charged FLA is good to -60 F. Another niche application is where one needs very high Charge and Discharge rates. Example in a place like Seattle WS where in winter they have less than 2 Sun Hours for much of the winter, and panel wattage's must be very high to recharge in a day which would give FLA battery problems. So before you consider AGM, consider is it worth the expense. AGM cost roughly twice as much as FLA for a given capacity, and last roughly half as long which means the long term cost of using AGM is 3 to 4 times more than FLA which is significant and a game changer once you are in the know.
      Thanks Sunking, very interesting did not see it from that perspective only been thinking about performance. Are you a battery engineer? cos I have more questions lol

      If one has 5 (12Vdc 240W 8A) panels in parallel into a 40A MPPT controller connected to bank of 4(12V 200AH) in parallel with good 8-10hrs of daylight how long/how many hrs to fully charge if AGM or FLA ?
      Last edited by wunmi007; 08-16-2014, 10:18 PM. Reason: spell check

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      • #4
        About 20 to 28 hours from the dead.

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        • #5
          Originally posted by wunmi007 View Post
          Thanks Sunking, ... Are you a battery engineer? cos I have more questions lol
          Dereck (Sunking) is not a battery engineer specifically, but is a PE who has spent most of his professional career designing off-grid power systems for commercial users.
          If you have enough questions (and appear to be a slow learner) I am sure he will quote you a reasonable hourly rate.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            Originally posted by wunmi007 View Post
            Thanks Sunking, very interesting did not see it from that perspective only been thinking about performance. Are you a battery engineer?
            No such thing as a Battery Engineer to my knowledge. I am an Electrical Engineer with 33 years or battery plant experience.

            Originally posted by wunmi007 View Post
            If one has 5 (12Vdc 240W 8A) panels in parallel into a 40A MPPT controller connected to bank of 4(12V 200AH) in parallel with good 8-10hrs of daylight how long/how many hrs to fully charge if AGM or FLA ?
            OK like I said you do not have 12 volt panels, they are 30 volt panels. Not to worry as they will work just fine on a 12, 24, or 48 volt battery system. Since you have a Prime number of panels, 5, you only have two configuration options open to you of either all in series, or all in parallel. Make note you have 5 x 240 watts = 1200 watts.

            Now the bad news. We cannot wire your panels in series to take advantage of much less expensive wiring and wiring losses. This means you must wire them in parallel which is BAD NEWS. Son dpoint since you have grid tied panels which is a good thing you must use a MPPT controller. Based on 1200 watt input and 12 volt battery you wil have to use a 80 amp MPPT controller, or really two 60 amp controllers because maximum charge current from 1200 watts is 100 amps on a MPPT controller.

            If you decide to cheap out and use a PWM controller, all you would need is a 40 amp controller. If you do that with your panels will change your 1200 watt panel into 12 volts x 40 amps = 480 watts. Just as well throw 3 panels away.
            MSEE, PE

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            • #7
              Originally posted by inetdog View Post
              Dereck (Sunking) is not a battery engineer specifically, but is a PE who has spent most of his professional career designing off-grid power systems for commercial users.
              If you have enough questions (and appear to be a slow learner) I am sure he will quote you a reasonable hourly rate.
              Whats his 411, for this project, replacing a 1000KVA (1MW) industrial generator in a factory wilt suitable solar system...anytakes:

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              • #8
                Originally posted by Sunking View Post
                No such thing as a Battery Engineer to my knowledge. I am an Electrical Engineer with 33 years or battery plant experience.



                OK like I said you do not have 12 volt panels, they are 30 volt panels. Not to worry as they will work just fine on a 12, 24, or 48 volt battery system. Since you have a Prime number of panels, 5, you only have two configuration options open to you of either all in series, or all in parallel. Make note you have 5 x 240 watts = 1200 watts.

                Now the bad news. We cannot wire your panels in series to take advantage of much less expensive wiring and wiring losses. This means you must wire them in parallel which is BAD NEWS. Son dpoint since you have grid tied panels which is a good thing you must use a MPPT controller. Based on 1200 watt input and 12 volt battery you wil have to use a 80 amp MPPT controller, or really two 60 amp controllers because maximum charge current from 1200 watts is 100 amps on a MPPT controller.

                If you decide to cheap out and use a PWM controller, all you would need is a 40 amp controller. If you do that with your panels will change your 1200 watt panel into 12 volts x 40 amps = 480 watts. Just as well throw 3 panels away.
                Sorry the panel spec is actually 3(18V 240W 13A) in Parallel connected to 40A MPPT controller and not 5(12V 250w 8a) as stated but bank is same and why did you say wiring in parallel is bad news?

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                • #9
                  Originally posted by wunmi007 View Post
                  why did you say wiring in parallel is bad news?
                  Because it is low voltage which means high current, which means many runs of large expensive copper wire.
                  MSEE, PE

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                  • #10
                    Originally posted by wunmi007 View Post
                    Sorry the panel spec is actually 3(18V 240W 13A) in Parallel connected to 40A MPPT controller and not 5(12V 250w 8a)
                    Very bad idea. Huge waste of money, power, efficiency, and materiel. Not to metion completely throwing away all the advantages of using a MPPT controller.

                    To put those panels in parallel means you need a combiner box with at least 4 circuit breakers (3-15 amp breakers and 1-50 amp breaker, and a large feeder cable going to the controller. If that distance is say 30 feet you would need #4 AWG copper conductor that cost around $1.25 per foot and you would need 60 to 70 feet of cable. You will have spent several hundred dollars in equipment trying to make it work.

                    Wire the panels in series and you do not need any breakers, combiner boxes, and only need to use 1 run of #16 AWG wire from the panels to the controller which will cost about $10 for the wire.

                    But please do it your way. Merchants want your money more than you need it.
                    MSEE, PE

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