OffGrid with LiFePO4 as energy storage

Steven Lake
Steven Lake Solar Expert Posts: 402 ✭✭
in General Solar Power Topics #1
http://offthegridstories.com/story/o...epo--as-energy

Here's an interesting little article I ran into. I've heard bits and pieces on these batteries and using them for solar. What's your thoughts on this? If they perform better in a discharged state than fully charged, it might actually interest me for some of my future installs where SLA and LA don't particularly work well due to being unable to reach full charge without using a ridiculously sized panel.

*EDIT* - It just dawned on me that this is a battery topic. Can a mod move this to the batteries section. I made a booboo and put it in the wrong forum. My bad.
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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #2
    I just ordered 4 prismatic 20ah LiFePO4 cells, that will hold about 0.25KwH for a little over $100. That's just 4 bare cells, not even assembled.
    If money is no object sure go for it.
    I don't think there is any point in using something so expensive unless you are using generator power to charge your batteries.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
    Just for your information, I'd question some of what you read on that web site. If you Google the author of the first story ( Dacian Todea ) manufacturers a solar BMS system for LIFeP04 batteries . As long as you know it's someone in the Solar equipment business, it's ok, they have a story to tell to. I don't know why he didn't mention it.

    https://www.google.com/search?q=Daci...utf-8&oe=utf-8

    [url]www.http://electrodacus.com/[/url]
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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #4
    Everyone wants to use LiFePO4 until they realize you are looking a $500 per KWH.
    Oh did they not mention that in the article?

    They also say that LiFePO4 is cheaper over the life of the battery compared to lead acid. Only until they accidently get discharged. At least with lead acid if you accidently kill them you can usually bring them back. I know with my LiFePO4 I take a big risk with that. One mistake, they're done and I am out a good chunk of money.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #5
    That's yet another reason I'm hesitant in gong with LiFeP04. In the event something does go wrong, you could wind up losing the whole pack! They're not really ready for the average off grid user. They may be very suitable for smaller, portable applications, where one is willing to balance the cells initially, and put in place a good BMS for protection. My main concern with them is I'm not convinced that their rated cycle life equates to calendar life. Especially considering the high up front cost.

    That' why I'm thinking of going the AHI route. Again calendar life is an unknown, but they appear to be a very safe and stable chemistry, and potentially could give very long service life, worth the risk IMO.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #6
    Huh, sounds almost like NiCD in the idea that, if you zero them out, you're pretty much done. Eh, not all that surprising given that every battery has its pluses and minuses. But still it's very interesting info.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #7
    oil pan 4 wrote: »
    At least with lead acid if you accidently kill them you can usually bring them back. I know with my LiFePO4 I take a big risk with that. One mistake, they're done and I am out a good chunk of money.

    That's what a low voltage disconnect failsafe is for. If THAT were to fail, and you discharged fully, you CAN recover them provided:

    A) You get to them asap.
    B) Apply no more than C/50 current until the cells reach about 3.0v. Then you may apply your normal charge current. Monitor.

    I have no specific timeframe for condition A. What is happening if you leave them in a fully discharged state is severe chemical degradation, which may or may not be accompanied by case swelling.

    Secondary damage comes from applying more than C/50 while they are down in the deep discharge knee.

    Ideally one builds a system from quality components, and designs their capacity needs appropriately. Even with lifepo4, I recommend designing around using no more than 50% cell capacity. That provides you a sliding windows of 100/50% SOC, 90/40, 80/30, 70/20, usually done by measuring current (coulombs in/out) because relying solely on voltage in the flat part of the curve is prone to error. Of course one should use an LVD regardless of chemistry.

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #8
    Steven Lake wrote: »
    Huh, sounds almost like NiCD in the idea that, if you zero them out, you're pretty much done. Eh, not all that surprising given that every battery has its pluses and minuses. But still it's very interesting info.


    I always like to here how the new battery technology would react to a failed charge controller with 80 volts of solar on a 48V battery for 2 days after a hurricane/lightning event in Mexico.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #9
    Dave Angelini wrote: »


    I always like to here how the new battery technology would react to a failed charge controller with 80 volts of solar on a 48V battery for 2 days after a hurricane/lightning event in Mexico.

    Catch fire and explode or explode and then catch fire, maybe.
    northerner wrote: »
    They may be very suitable for smaller, portable applications,
    They do. My LiFePO4 starting battery in my diesel saves about 100 pounds of weight.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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