Are AGM's better than FLA's?

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tabbycat
tabbycat Solar Expert Posts: 55 ✭✭✭
in Off Grid Solar & Battery Systems #1
Assuming your only charging source is solar it would appear that AGM's do a better job at preserving solar output. A UPG AGM loses about 15% of its' capacity in freezing temps while a Trojan FLA will lose 30%. The UPG will self-discharge at 3% per month while a Trojan will lose ~10%. Considering how difficult it is to collect those solar amps you don't want to lose them in the battery bank. Does this seem like a reasonable conclusion. Thanks.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #2
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    Re: Are AGM's better than FLA's?

    I prefer dollars and cents(sense). Higher costs make them a poor choice for me.

    I actually though cold temps were equal across lead acid batteries.

    3% vs 10% across a month isn't worth worrying about. Some/most AGM charge at a higher efficiency though.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
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    Re: Are AGM's better than FLA's?

    Hi "tabbycat", welcome to the forum.
    My opinion, and others are free and may well disagree, is that in a "normal" solar settup the 3% or 10% per month loss is not a real issue, especially at today's low cost of solar panels. It could be an issue however if you were to shut down your system and leave it shut down for an extended time with no charging taking place. That said, there are other reasons to pick one or the other. Generally AGM batteries will accept a higher charge rate and can discharge into a heavy load faster than FLA. AGMs also do not need water added, they don't normally gas off, so don't need ventilation. Sounds great right? Well there are also a few negatives to AGM over FLA. Cost of batteries to start with. They are generally considerably more expensive to purchase. They are intolerant of abuse such as overcharging compared to FLA, you cannot check their state of charge via SG readings, and generally they don't last as long.
    As to loss of capacity when cold? I used to worry about that, but after almost 15 years living with FLA, for me, in my situation, it's basically a non issue. At the moment, the air temperature here is minus 22C, almost minus 8F. Battery bank temperature is minus 7C, 19.5F and all is well. Some years I insulate the battery bank for Winter and that tends to limit temp drop to roughly the freezing point (0C, 32F), this year, so far I haven't bothered with insulation. Biggest "problem I've found over the years is that with lower battery temps, the Charge Controller boosts the absorb voltage as required for proper charging, colder the batteries the higher the voltage, and if you have an inverter that shuts down on over-voltage of 15.5 or less, it will shut down until the voltage drops back down. The inverters I have running now will operate up to 16.5 volts, so shutdown is not a problem.
    Hope this helps answer at least some of your questions and I'm sure others will add their thoughts/experience.
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  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    #4
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    Re: Are AGM's better than FLA's?

    Hi "tabbycat", while my opinion may be biased due to the fact that I have AGM's, I can list a few things I've noticed since changing over to AGM's from FLA's.

    1) Efficiency is great! Lower charging voltage results in higher current from PV, especially with MPPT. Higher discharging voltage results in less current draw for the same wattage load.
    2) Very small polarisation effect (the skin affect on battery plates that causes voltage to deviate significantly from the resting voltage when under load or charging). This enables far more accurate SOC estimation from battery voltage. A simple table can be set up that allows you to work out what the state of charge is depending on the load and temperature of the battery.
    3) They are clean, spill proof and do not emit any gasses provided you don't exceed the recommended charging voltage.
    4) Low internal resistance - which in my mind is always better in every way.

    As others have said though, intolerance to overcharging is a drawback, so just make sure it doesn't happen at all costs. I would not recommend using AGM's unless you have very stable temperatures in the battery room or a charge controller with good temperature compensation set correctly and with the thermometer attached securely to a battery terminal.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
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    Re: Are AGM's better than FLA's?

    AND, generally, AGMs are rated for fewer discharge/charge cycles, compared to Flooded batteries. So, if the target system is a typical off-grid system, the batteries should be expected to have a shorter lifespan -- perhaps half as long for a similarly sized bank vs Flooded batteries.

    Most manufacturers specify the number of cycles verses the Depth Of Discharge.

    Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    #6
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    Re: Are AGM's better than FLA's?
    Vic wrote: »
    AND, generally, AGMs are rated for fewer discharge/charge cycles, compared to Flooded batteries. So, if the target system is a typical off-grid system, the batteries should be expected to have a shorter lifespan -- perhaps half as long for a similarly sized bank vs Flooded batteries.

    Most manufacturers specify the number of cycles verses the Depth Of Discharge.

    Vic

    Maybe traditionally speaking, however now there are AGM batteries on the market that compare favorably with FLA's on a cost-per-cycle basis (Look up SonX batteries). Many FLA's never reach their expected life because they need so much attention and mollycoddling throughout their lives (watering, equalizing, SG checking etc). Yes, AGM's are the lazy, uneducated man's batteries but that's fine with me;)
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #7
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    Re: Are AGM's better than FLA's?
    CALLD wrote: »
    ... Many FLA's never reach their expected life because they need so much attention and mollycoddling throughout their lives (watering, equalizing, SG checking etc). Yes, AGM's are the lazy, uneducated man's batteries but that's fine with me;)

    Opinions do differ on this. FLA batteries are used in the vast majority of off-grid systems. There are a number of good reasons for this.

    Lead-Acid batteries DO need attention -- AGM, FLA, and Gel.

    One huge advantage for the FLAs is the ability to ACTUALLY MEASURE the SOC quite closely. Flooded batteries do need water on occasion, and an occasional EQ.

    But, seems to me that LA batteries that are sealed, even more attention needs to be focused on them, trying to discern just what IS the SOC, and what to do about any inferred low SOC, and, then, just what might be the resulting change in SOC, based on any changes made, from trying to improve the SOC, and so on.

    This has been beaten to death here, but like most things in life. There is no single or simple answer -- just many, many trade-offs that need to be applied to the needs of the application for energy storage.

    Just wanted to toss out a couple of things to put my thumb on the scale. FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • SandyP
    SandyP Solar Expert Posts: 65 ✭✭
    #8
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    Re: Are AGM's better than FLA's?
    Vic wrote: »
    Opinions do differ on this.

    It also appears that opinions are formed on battery types when using batteries not made for RE use.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #9
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    Re: Are AGM's better than FLA's?
    CALLD wrote: »
    ...AGM batteries on the market that compare favorably with FLA's on a cost-per-cycle basis (Look up SonX batteries)....

    I'm always interested in advancements, so I checked them out, looks like all the web sites that sell them are from South Africa, so hard to know what prices are we're talking about, might put your location in your header CALLD.

    But from the specs of a 260 amp 12 volt; Approx. "...1300 cycles @ 30% depth of discharge" Which I would guess is a tad longer than golf cart batteries so they would have to cost less than 3x the cost of inexpensive 6 volt 220 amp hour, Golf cart batteries to be cost effective. NOT going to be cost effective importing them into the states. Does appear to be a float type battery for situations with higher usage, thicker plates for more cycles.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #10
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    Re: Are AGM's better than FLA's?
    SandyP wrote: »
    It also appears that opinions are formed on battery types when using batteries not made for RE use.

    Yeah...No... Batteries don't care where the energy comes from or goes to... RE batteries while not all hype are only a bit better designed for typical off grid use. Often they tend to be less cost effective, since fewer are made for RE use than other batteries with very similar characteristics built for other types of use, Golf Carts, Floor Scrubbers, Fork Lifts...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • H2SO4_guy
    H2SO4_guy Solar Expert Posts: 213 ✭✭✭
    #11
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    Re: Are AGM's better than FLA's?

    Hi tabbycat,

    I have both flooded and AGM and while waiting for that 'Revolutionary' new battery that is going to change everything that seems to come along at least once a month, I decided to go as cheap as possible on batteries and focus more on charging solutions with more solar. Most of my batteries are purchased for not too much over scrap value. I have about $2000 in batteries and that works out to around 2500 AH at 48 volts DC. I type this to you while running 2 electric heaters. How many off-grid folks heat with batteries? I have had them about 15 months or so with no generator run time. Zero gas. I have had to heat with propane when we have had extended periods of almost no direct sunlight.

    The Panasonic stationary batteries are kick-butt. They just sit there and do their thing. The only maintenance has been to retorque the connections. That's it. As the individual 2 volt cells fail I have spares that are of the same age and type to plug right in. We will see how this works out.

    Good luck and let us know how it works out.
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
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  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    #12
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    Re: Are AGM's better than FLA's?

    At the end of the day it's the batteries that put a smile on your face and cause you the least amount of stress that come out tops. As far as the ability to measure SG is concerned I say "you can have it". I still have some of my old FLA's and spent nearly 2 weeks with them on trickle charge to get the SG in all the cells up to 100%, I now keep them for emergency backup only. My AGM's charge up to 100% quickly and without fail every time, discharge curves are consistent and high every time. Had them for three months now, never been happier. With my old FLA's I was worrying from day 1, just never seemed to get them fully charged on solar alone, they just never had enough time on absorb...
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  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #13
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    Re: Are AGM's better than FLA's?

    My AGM's are the shizz-bit. I wouldn't part with them for twice the size in FLA's. They sit there do their thing and charge so fast, I figure what I save in gas more than makes up for the cost difference. In my case, I get none, like zero solar help from Nov-Feb so I charge and I usually charge morning and night. My "battery bank life-time" should be 1/2 of a normal single daily recharge cycle. After two interior winters with high discharge/recharge rates. My bank has lost zero capacity. As a matter of fact I would say it is working better than last winter. This bank is three years old, but has been used at twice the norm of most RE banks.

    For what it saves in fuel, time, worry, the higher cost is not an issue for me, but like others have said. Which batteries give you the warm and fuzzies? Those are the ones to use.
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