Longevity of AGM vs LiFePo4 in high temperature environments

magicbus
magicbus Registered Users Posts: 10 ✭✭
in Off Grid Solar & Battery Systems #1
Just to be clear, my specific application is RV / mobile, but the question is applicable to fixed-site installs as well. I'm trying to decide between AGM & LiFePo4. I'd frankly rather go w/ AGM, despite the weight/size disadvantages, as I'm much more familiar with them. But I have one major concern: The heat. We're in Phoenix, and the batteries will be located in an unconditioned metal shell (a bus). This last summer I read 134 inside at the peak of the day. Granted, this won't be every day. Especially not when we're on the road. But more days than not, the temps will be what most batteries would consider hostile. I'm fairly certain LifePo4 would be better in this regard. What I don't know is how much better. Given the extra complications & up-front price, would LFP be a net win for my environment? I don't want to spend $2500 or more on an AGM bank that dies in 3 years. But I also don't want to spend 3 times that on an LFP bank that dies in 5. What would you do?
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    LiFePo aren't going to like really high heat either.

    While not specific to this chemistry, this gets into some detail:
    https://batteryuniversity.com/index.php/learn/article/bu_808b_what_causes_li_ion_to_die

    Summarizing; a fully charged lithium battery in high heat can degrade fairly quickly.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    edited November 2019 #3
    I cannot give you real life experience with LiFPo4, but I can tell you about thousands of AGM batteries - using high quality models.
    A motor coach or tour bus running the Phoenix, Palm Springs, Las Vegas highways will generally get 5 years of service life. Using temperature recorders, we measured 140F-155F battery temps regularly, in this application.YES, heat dramatically reduces AGM battery life! The identical application in Northern climates are on a 7-9 year replacement cycle.
    Cooler is better, but speak with your battery supplier about the specifics of your application. If they do not tell you to expect a 50%-70% reduction in lifespan, they do not understand what you are asking.
    Extreme cold is actually good for AGM battery lifespan, but you will see a reduction in capacity as the battery temperature falls. Good AGM's do not freeze until they hit -90F to -95F when fully charged, and it's a curve down toward zero charge level. Quality AGM's have around 90% capacity at 20F, dropping to 55% capacity at 50% state of charge and about 35% at -40F. (We do a lot Arctic applications)
    Sure, I have read blogs and supplier literature on LiFPo4, but I have ZERO actual field experience for an RV. Anyone can quote Google, so I suggest speaking with people who have dealt with your application.
    Remember that like most things, all AGM's are not created equal. Work with a manufacturer who publishes the kind of data talked about above.
    Marc

    I always have more questions than answers. That's the nature of life.
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  • magicbus
    magicbus Registered Users Posts: 10 ✭✭
    #4
    That's very useful, Marc. Thank you so much!

    For what it's worth, I'm thinking Lifeline AGMs. If I could get 5 years w/ them in my climate I'd be happy. I'd be paying at the very least double that for LPF, which I'd be suspect of lasting 10.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    #5
    magicbus, If you can get twice the life, at twice the cost - you are even - depending on the value of your invested capital. If you go Lifeline, we should talk about charging because their requirements are different that everyone else. (I don't sell chargers, I am an application specialist)
    Marc

    I always have more questions than answers. That's the nature of life.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited November 2019 #6
    Having observed the effects of high temperature on both FLA and LFP, the FLA would increase in temperate over time due to inability to cool sufficiently overnight due to la tent heat. When maximum ambient was 40°C for overy a week the FLA temperature would  increase to~50°C, the LFP on the other hand remained below ambient usually by ~5°C. 

    AGM are more efficient than FLA so self heating would probably be less, another facor could be the FLA were monoblock GC batteries, the LFP are single cells which results in greater surface area for overnight cooling. With LFP the BMS should provide high temperature protection, the BMS I use disconnects the battery at 70°C. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    #7
    Yep, but remember that In Phoenix and the rest of the valley, 40C at midnight is not unusual after the "summer heat switch" gets activated! Batteries sitting in a metal box called an RV, at 120+F ambient creates some interesting challenges. The add the reflected heat from the asphalt.
    My approach would be to investigate what happens to LiFPo when charging and discharging at 120F to 140F, Then repeat the process at low temperature.
    Again, I have zero field experience with LFP- the current generation may be fine at extreme temperatures!
    Marc


    I always have more questions than answers. That's the nature of life.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #8
    Marc Kurth said:
    Yep, but remember that In Phoenix and the rest of the valley, 40C at midnight is not unusual after the "summer heat switch" gets activated! Batteries sitting in a metal box called an RV, at 120+F ambient creates some interesting challenges. The add the reflected heat from the asphalt.
    My approach would be to investigate what happens to LiFPo when charging and discharging at 120F to 140F, Then repeat the process at low temperature.
    Again, I have zero field experience with LFP- the current generation may be fine at extreme temperatures!
    Marc


    The effects would be different without overnight cooling, my observations were where the minimum temperature is close to 30°C, usually after midnight in a room in free air, not a s box. The primary reason I changed to LFP was temperature and I'm very pleased with the results, all other benefits are welcome additions. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,170 ✭✭✭✭
    #9
    Sounds like high temps are not a problem. That's good to know!
    Marc
    I always have more questions than answers. That's the nature of life.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #10
    And since you are in an RV--Are you going to hit seriously cold areas? Will the battery bank be "insulated/ventilated box"?

    Li Ion batteries generally do not like to operate below freezing (or as low as 25F). If your bus gets cold soaked in a mountain/far north region, an insulated or even heated battery box could be required.

    As Marc says above, AGMs (and any FLA battery) is a better choice for cold.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • magicbus
    magicbus Registered Users Posts: 10 ✭✭
    #11
    Great info, folks! Sure do appreciate the input.

    Below freezing? Nope. The wife has already told me we're not going anywhere cold!  :) 

    Seriously though, the box will be inside the vehicle. It's not the times we're traveling - where the space will be heated or cooled as required - that I'm concerned with. It's more the months it's parked at home I'm worried about.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #12
    Remove the batteries when parked, they will need to be charged periodically especially LA, LFP have extremely low self discharge.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • magicbus
    magicbus Registered Users Posts: 10 ✭✭
    #13
    I had considered doing that, mcgivor. And I haven't stopped considering it. But disconnecting/reconnecting, and moving 120# batteries in & out of a short bus every time it's parked for a week is going to be a real pain. Enough of a pain that I doubt I'll keep it up for long. If I was just parked for the summer it wouldn't be a problem. But our trips will be more frequent, short get-aways than seasonal expeditions. The irony is with LFP it wouldn't be nearly as much of a hassle.
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