Lithium Battery questions...Cold temps, capacity vs FLA etc

icarus
icarus Solar Expert Posts: 5,436 ✭✭✭✭
I’m sure much of this has been covered in various other threads, but I’m too lazy to search too far.  Designing an off grid system, will be used ~100 days per year (summer only). Daily consumption ~5-7 kWh.  The system will be completely unattended for the offseason.  

First question, I am pretty well versed in the design criterion for FLA batteries, and sizing battery banks for such systems drawing a daily max of 25-50% (and total estimated charge cycles)

My first question is, how do I compare the relative capacity of different types of batteries .  For example, MY current system has a total (100%DoD) of ~500ah.  What would a similar LI battery need to be comparable?

Second and ultimately more important is long term winter storage of a system that CANNOT be outside heated, can routinely get to -25f, can occasionally get to -40f (or colder).  A minimal charge regimen will always be available but probably not enough to support any aux heat.  Question is, if I shut the system down in early fall, with the batteries at 100% SoC, leave them off all charge regimen over the winter, will that damage them.  Alternatively, if I leave them on the PV and gather battery temp drops, will they be damaged charging.  Are there charge controllers that have BTS systems that stop charging when they batteries are too cold?  Are there battery designs that are out there that provide a bit of self heating (ala Tesla) that don’t over draw when on a small PV system?

Clearly, from a total kWh cost LI batteries beat FLAs hands down under normal situations.  Total number of cycles, ability to deliver more of total capacity per cycle etc is clear.  What isn’t clear (yet) if they make sense for an application such as mine,  

Thanks in advance for any and all learned advice.  I will try to check back when I can, but I will be incommunicado for a while so don’t think I am ignoring your thoughtful responses.

As always,  with kindest regards,

Icarus

Comments

  • MichaelK
    MichaelK Registered Users Posts: 234 ✭✭✭
    Here's a thread on another board discussing what went wrong with a Li battery pack left in a car for days, exposed to temperatures that dropped down into the 20s.  The pack appears to be dead now, even though the pack was not charged while cold.
    Might be of some value to read before making a decision?

    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,142 ✭✭✭✭
    edited January 2021 #3
    This is Off Topic in terms of your question but:
    As you know, good quality AGM's can run down to (-)90F at 100% SOC and (-)50F at 75% SOC without freezing. With a self-discharge rate of 1% per month under cool/cold conditions, 11 months of sitting seems like a decent application of AGMs.
    With only 100 charge/discharge cycles per year, you can go down to a 70% DOD it will take a while to reach 600-800 cycles, with occasional excursions much deeper.
    Marc
    I always have more questions than answers. That's the nature of life.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Marc.

    To be clear, we CAN charge throughout the winter as the PV is abundant.  The question is CAN we with the battery temps as mentioned, and or, can they simply sit idle?  

    Tony

    PS. Thanks Micheal, will read it.  

    T
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    When I changed from FLA to LFP my choice was to replace 400Ah at 24V FLA with the same nominal capacity LFP  because during 3 months of the year my daily useage is 5-6 kWh, thus pushing the FLA  DOD envelope. The general rule of thumb is to use the 20-90% range for LFP, doing so is supposed to increase the cycle expectancy dramatically from the <2000 cycles at 100% capacity discharge, some say up to 10,000 or more. This makes the cost of lifetime energy about the same as FLA, using raw cells in a DIY bank would be less, assuming 25°C, due to high temperatures both my FLA banks started to show signs of lost capacity at around 500 cycles.Currently with 850 cycles on LFP everything is as when installed all cells have remained ballanced and no sign of lost capacity.

    This link will answer questions about storage https://batteryuniversity.com/learn/article/elevating_self_discharge?__cf_chl_jschl_tk__=807725ffb31488eec760c406981f94511bf74a05-1609641791-0-AZySUr-uOtcUQU7IRhy83HmdffPGQuZFHBH1gXiOpcJ7Sp0mnwBsn5Aa-OxoD6IYWD1LXnhB8_AWVNV41G55QBmE0gn2dE06gESkdbOoXIniGWnAhiKzaQr9I36wlthnY9ogrsAH3Ory27QiYfXrRkD0mrk3RWv42UlJiM3xwTny72RCC3XHv0hQmK5dfwAeCLplBMLgbnClWS70Dn2bG8SSKyebLWEE6ned7dORxSdrKGZXgR_k7YaIBpyLrWBIKMiWstgA8LL7iWxMLOaI47R4bxiPOVtOL-PLcMtzQr0sLWjaaWtUtDC_VaSnI-p3Kq_yxoy6QNusbYxlT0qGcYvhuboLGee0z1k9e2iT-ATh

    LFP based on my research have a self discharge of 1-2% at 25°C which is about half that of LA, they should however be stored at 40-50% capacity not fully charged. Cold weather is not something I'm personally concerned with but this link   https://www.ufo-battery.com/how-to-store-your-lithium-ion-battery-in-winter will point you in the right direction.

    The attached pdf has a wealth of information, much of my studies was reading as much as possible, I'm a little skeptical when it comes to numbers based on accelerated testing for all batteries, but it's probably not practical to wait 10 years or more for results. So far I'm extremely satisfied, the real advantages are the rates of charge and no long absorption, perfect for summer here in Thailand where it's often cloudy in afternoon. 
    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.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    edited January 2021 #6
    Thanks Mcgivor.  Looks like I have my evening reading to do...Tony

    ps.  Having trouble opening the pdf with IOS.  
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    icarus said:
    Thanks Mcgivor.  Looks like I have my evening reading to do...Tony

    ps.  Having trouble opening the pdf with IOS.  
    Check your  mail inbox, sent screen shots, hopefully in correct page order.
    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.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Got em!  Thanks...Tony
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    My 2 cents worth:  Li is not going to work in the cold like this.   Consumer electronics barely make it to -10F, after that , things start breaking.

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    MIke,  I know we had a very similar conversation a year or so ago about my own system.  As I said I am designing a system for a client,a nd was wondering if the technology is/has advanced far enough to consider.

    Tony
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    There have been a few small, incremental advances, but if that was my install, I'd use FLA or AGM and leave them on a light float charge over the winter
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Wheelman55
    Wheelman55 Registered Users Posts: 233 ✭✭✭
    edited January 2021 #12
    We are using the Discover batteries with seasonal use opposite of your’s. 29 degrees latitude. We leave in the summer and return in the fall. 

    The Discover batteries have an off switch which lowers the drain over the six months we are away to very little. We shut our system down in the off season. 

    These batteries do not like extreme cold, however they are light enough to carry them home with you at season’s end. 

    It would take two of the Discover 130 ah 48 volt batteries to match your 500 ah flooded. 

    We consume 30 ah overnight which gets filled in about 30 to 45 minutes after the sun hits them. We’ve got 5,000 watts on a single axis tracker (thanks Dave Angelini!), so the panels produce well even at first light.

    This morning the sun hit the array at 8:15 am and we got to 100% SOC at 8:45 am. 

    We use Schneider gear with the XANBUS, so it’s a closed system. 

    As an experiment I ran the battery down to 0% SOC two days running. The battery shut itself down at 0% and disappeared from the SCP display. The battery restarted each morning once the sun hit the panels and showed again on the SCP. XANBUS seems to be working as advertised with the Schneider gear and the Discover AES battery. 

    At 0% SOC there is still charge left in the battery. My guess is that the BMS only allows 80% of the batteries real capacity to be used. Likely keeping the battery between 90 and 10 percent. 

    So far very happy with the batteries. They should outlast me:)
    Off-Grid in Terlingua, TX
    5,000 watt array - 14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048NA+, Mini PDP, MPPT 80-600, SCP. 390ah LiFeP04 battery bank - 3 Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    I got a comment back from Lion battery.  In short “Too cold for our batteries to be used, and way colder than any testing regimen we have used”. I guess that is the ultimate answer.  I will think about a self heating regimen and maybe try a beta sometime (on someone else’s nickel I hope.  Thanks for all your helpful comments,  Tony
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    What about making a portable power station that can be moved when not required, my latest endeavor was the replacement of my secondary LA bank with LFP, since the future of this system is another location I decided to assemble everything, except the array of course, to something that could be relocated with minimal effort.

    The pictures are of my almost  finished product, a welded square tuber frame with plywood covering, the inverter will be mounted on top to maintain the shortest possible conductors. The cells are 200Ah CALB for a nominal 24V, the total weight including inverter is 62Kg (136 lbs) for a conservative 3.6Kwh, based on 20% to 90% SOC. There would be no reason why this couldn't be expanded into two units using interconnect cables, the second being a battery expansion to 48V, perhaps with Anderson connectors for the array as well as battery.

    My biggest problem is access to hardware, primarily to quality electrical components with short lead time, there will be improvements and insulation to exposed terminals in case that is a question. Real estate was limited as well, making it difficult to have everything level  considering knockout locations, the final product will be more attractive.

    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.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    The site is 100km from town, and transporting stuff involves multiple boats, then bush road, then a place to store the stuff.  Not as hard to do as with FLAs but still a pain.  Also, in the case of my personal site, we actually use it in the winter, so when we leave, we need it at the ready when we return.  Transporting batteries across the ice by snowmobile is not in the cards.  

    Tony
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Been digging a bit deeper.  Victron LiPo batteries can be stored as low as ~-40F (C) It cannot be charged below +5 C (~40f). My newest question, perhaps redundant, is this.  Once again, if this battery is shout off from all charge/discharge, and left with ~80%SoC for up to nine months will that hurt the battery?  In my case, if I leave my place in the winter I can simply shut the system down, and even if I return to a house that is -30 inside, it is an easy matter to simply heat the battery up to +5 in a matter of a couple of hours.  I don’t need power for those couple hours.  Will this be an acceptable regimen and will I be happy in this or am I running too great a risk on an expensive battery.

    I routinely use ~10-15% of a string of 4 t 105s every day, or about 75 ah.  I am guessing that the 100ah LiPo would be a fairly good equivalent battery.  Opinions?  Thanks ,

    tony
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    If you are allowed to store to -40c   and you always warm the innards of the battery to +5c before charging , I'd say you are good to go.  

    Long term storage, the bare battery is OK, but if there is an integral BMS, it might have/be a vampire load and drain the battery while it's monitoring it.   See what the Mfg states about how long you can store..
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    icarus said:
    Been digging a bit deeper.  Victron LiPo batteries can be stored as low as ~-40F (C) It cannot be charged below +5 C (~40f). My newest question, perhaps redundant, is this.  Once again, if this battery is shout off from all charge/discharge, and left with ~80%SoC for up to nine months will that hurt the battery?  In my case, if I leave my place in the winter I can simply shut the system down, and even if I return to a house that is -30 inside, it is an easy matter to simply heat the battery up to +5 in a matter of a couple of hours.  I don’t need power for those couple hours.  Will this be an acceptable regimen and will I be happy in this or am I running too great a risk on an expensive battery.

    I routinely use ~10-15% of a string of 4 t 105s every day, or about 75 ah.  I am guessing that the 100ah LiPo would be a fairly good equivalent battery.  Opinions?  Thanks ,

    tony
    Wouldn't 75Ah of a string of 200-220 Ah be more in the region of 50% discharge capacity, using 210 Ah as a median capacity of 24V nominal battery string.?

    A 100Ah 24V LiFePo4 bank may suffice but it is pushing the limits, in my opinion, replacing like for like in terms of capacity will safeguard aginst days of low PV return, also extending the service life with low discharge rates. Naturally cost is a consideration, buying pre manufactured batteries may seem the easiest choice but building a DIY  bank with top of the line cells would be significantly less expensive including a BMS, and it's not rocket science, only 9 extra wires for 24V nominal and programming of the charge controller  is way easier than that of lead acid batteries.  

    The low temperature  storage of all LiFePo4 are equivalent, be they individual cells or drop in replacement batteries, there are BMS systems which consider low temperature charging exclusion in a DIY bank, however I've had no need to consider them being in the tropics, but they are available, research will reveal the nessersary equipment.

    Also a key point is to store LiFePo4 at approximately 50% SOC, their capacity will be greatly reduced at lower temperature but will return as temperatures increase, this is related to the internal resistance correlation to temperature. Just some thoughts.
    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.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I've considered a similar, warm-before-use, sort of thing.  One potential issue that I'd want to know was overcome would be reading the lowest temperature in the block of cells.  Presumably, multiple sensors would be needed in various interior and exterior locations to be certain the entire block is warm enough.  While warming, the interior cells could stay pretty cold after the exterior ones get warm enough, and the reverse when cooling down.
    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
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The method users in the EV world recommend is to place a small  load on the battery such as headlights, to generate heat within the cells before using them to drive,  how well this works is unknown to me personally due to having no need nor environment to do so. EV forums would be a source of information that may be of interest.
    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.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    To be clear...currently configured for 12 vdc. 4 T-105s 225 ah @6 volts, leaving ~450 ah @12 vdc.  

    If I wire this with a single battery, (and overcome any BMS self discharge) then simply unwiring the battery is very simple, and it can then be moved to a heated space (next to the wood stove for example) until it comes up to or above design temp.  Reheating the battery, given is small thermal mass should not take longe than a matter of a couple of hours.  I suppose I could heat it in a water bath if I was a in a hurry.  

    Back to sizing, give my current loading of say 1kWh/day, what might a good compromise battery size be?  At a 50% DoD, a 100 ah LiPo would give me ~ 600 wh/day.  I’m thinking that oils be a bit too small, but 160ah would give me just over 2kwh/day at 50% DoD.  That would give me ~3 days of autonomy.  

    Once again thanks for the ideas.  

    Tony

    PS I am trying to find contact for Victron an have been having some trouble 
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    With regards to capacity a 12V nominal, 100Ah would provide approximately 0.8 kWh, using a formula of average voltage of 12.5V, and a conservative 70% of capacity, it must be noted that most of the usable capacity is actually in the 13V plus range but it's prudent not to overestimate things. Going with 200Ah  would probably be a better target to aim for, if cycle life is of importance, currently I'm experimenting with a 200Ah bank at 24V nominal with a daily useage of 1.5 kWh, which is about perfect, never depleting the SOC to below ~ 50%.

    Most inverters have a low voltage disconnect of 10.5V which is designed to protect the inverter using lead acid batteries, this value is far to low for use with LiFePo4, there would need to be some means of disconnect at a minimum of 12V, preferably slightly higher, just some other things to ponder, this is easy to do with a voltage sensing relay and a high current low consumption contactor such as this https://www.alibaba.com/product-detail/ODOELEC-High-Load-Current-High-Voltage_60793503571.html?spm=a2700.galleryofferlist.0.0.e98a31d3U1nrCn There are other  ways to skin the cat using sophisticated stand alone computers but using such devices for such a simple task seems overkill, IMHO, but each to their own. One may think, oh I don't need that because I will know when things are not right, but like a seat belt or airbag, they protect the unforseen.
    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.