Pros & Cons of Lithium-ion batteries for solar application

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  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    In a RE system using Lithium batteries you would likely have the inverters low voltage cut off set well above the low cut out of the BMS. So no disconnection from the battery should ever occur.

    Likewise the charge controller would be set up to prevent any charging up too close to the high voltage limit. No need for diversion loads.

    This is how all battery based Solar systems operate as far as I am aware.

    I see your point about cell imbalance making this problematic but the BMS should prevent this, no? Yes, the BMS cell balancing function would be critical. People are using LiFePO4 in solar applications so it must work.:confused:

    The Low voltage and high voltage limits in the BMS would simply be a fail safe to prevent damage to your battery bank in case the inverter or charger were not programmed correctly. No need for any direct communication between BMS and other components.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    mtdoc wrote: »
    I

    The Low voltage and high voltage limits in the BMS would simply be a fail safe to prevent damage to your battery bank if the inverter and charger was not programmed correctly. No need for any direct communication between BMS and other components.

    True as far as it goes. The BMS will often incorporate temperature compensated settings, as well as circuitry to interrupt the charge cycle if any cell goes over the temperature limit.
    The CC should at least have a remote temperature sensor to measure the battery temp, as well as temperature compensation of its voltage setpoints which match the temperature coefficients for that Lithium chemistry, which may well be different than the corresponding coefficients for any Lead Acid cells.
    SMA SB 3000, old BP panels.
  • FatawanFatawan Solar Expert Posts: 71 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    I have been looking into Lithium batteries recently. I too think they are the future. Cheap solar got me thinking that I should be adding more panels, driving plug-in hybrids, and even storing electric for backup in emergencies. I am thinking large lithium is a better idea than a generator. This company seems to be the cream of the crop:

    http://www.corvus-energy.com/index.html

    Not cheap, of course, but looks like a very good product. I think I read something like $1000/kWh maybe??? When you start to compare to a large generator, it's not so bad.

    Also, GM/ABB are jumping in with old Volt batteries

    http://media.gm.com/media/us/en/gm/news.detail.html/content/Pages/news/us/en/2012/Nov/electrification/1114_reuse.html
  • RCColaRCCola Registered Users Posts: 5
    Re: Pros & Cons of Lithium-ion batteries for solar application
    Fatawan wrote: »
    I have been looking into Lithium batteries recently. I too think they are the future. Cheap solar got me thinking that I should be adding more panels, driving plug-in hybrids, and even storing electric for backup in emergencies. I am thinking large lithium is a better idea than a generator. This company seems to be the cream of the crop:

    http://www.corvus-energy.com/index.html

    Not cheap, of course, but looks like a very good product. I think I read something like $1000/kWh maybe??? When you start to compare to a large generator, it's not so bad.

    Also, GM/ABB are jumping in with old Volt batteries

    http://media.gm.com/media/us/en/gm/news.detail.html/content/Pages/news/us/en/2012/Nov/electrification/1114_reuse.html

    I'm not sure why you think these are so great, the batteries themselves most likely are only rated for 2000 cycles to 80% discharge (I found on their website they are powered by dowkokam cells) This is quite common.

    http://www.dowkokam.com/tech-cells.htm

    Yes they are prepackaged they however are not combined with a solar inverter/charger/mppt/etc so you are not much further along then doing everything yourself.

    Winston batteries claim 3000 cycles to 80% dod 5000 if I remember right to 70% Dod, combine that with an Orion BMS and you are probably further ahead then the corvus system (more cycle life). The big problem is getting other components to work properly.

    If money isn't an option Victron, MasterVolt, and Clayton Power have complete systems. They are however extremely expensive.

    As soon as standard off the shelf inverter/charger & mppt equipment from companies like xantrex, outback, magnum, etc begin communicating with generic BMS equipment then the price will fall quickly for this technology. Until then it is probably possible however not real easy to get a safe reliable system for a reasonable amount of money.

    (If you look at the solar bodger's site he also linked to a report from a european university that tested the winston cells to 10000 cycles with little to no reduction in battery capacity)

    Sony apparently also has a lithium sytem that looks fairly awsome that apparently works with smc equipment. Looks great, then again out of my budget.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Some Lithium based systems are becoming available in Europe, there this:
    http://www.akasol.com/en/storage-for-renewable-energies/neeoqube.html which is the battery and BMS integrated into 1 unit. 3000 cycles to 80% DoD.

    And there's a new all-in-one inverter/charger/MPPT tracker: http://powerrouter.com/products/powerrouter-solar-battery-self-use-li-ion which supports charging lithium batteries, but no details on the batteries themselves.
  • RCColaRCCola Registered Users Posts: 5
    Re: Pros & Cons of Lithium-ion batteries for solar application
    stephendv wrote: »
    Some Lithium based systems are becoming available in Europe, there this:
    http://www.akasol.com/en/storage-for-renewable-energies/neeoqube.html which is the battery and BMS integrated into 1 unit. 3000 cycles to 80% DoD.

    And there's a new all-in-one inverter/charger/MPPT tracker: http://powerrouter.com/products/powerrouter-solar-battery-self-use-li-ion which supports charging lithium batteries, but no details on the batteries themselves.

    Thanks for the response, the power router unit is exactly what I am looking for. Off the shelf inverter/charger that is compatible with 3rd party lithium ion battery systems. This one looks ideal and has the added advantage of having the mppt built in. Hopefully they will come up with a 120/240volt unit to sell in the us.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Here's another, inverter/charger and battery in one unit: http://www.tritec-energy.com/en/complete-systems/tri-cell-the-efficient-storage-system-for-solar-power-c-176/
  • Chuck46Chuck46 Solar Expert Posts: 95
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Here is a link to some folks that are living in a bus with LiFePO4 batteries

    http://www.technomadia.com/category/life-on-the-road/technology/lithium-ion/

    And here is a response from MidNight Solar when I inquired about using said batteries with their charger

    Aloha Charles,As long as the Li battery's BMS allows it to be a source as well as a sink, there should be no problems.Cheers,TomTom Carpenter Technical Sales 360-403-7207 Ext.150On 10/29/2012 1:07 PM, [email protected] wrote:
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    Chuck46 wrote: »
    Here is a link to some folks that are living in a bus with LiFePO4 batteries

    http://www.technomadia.com/category/life-on-the-road/technology/lithium-ion/

    Great link. Thanks!
  • nut17nut17 Registered Users Posts: 5
    Re: Pros & Cons of Lithium-ion batteries for solar application

    This is a link to the NZ supplier that I recently purchased a 200 AMP / Hr Lithium Iron Phosphate Yttrium Battery from: http://www.aasolar.co.nz/AA%20Solar%20Lithium%20Deep%20Cycle%20Batteries.html I have had the battery installed and in regular use since April, and compared to the AGM,s I was using before this battery is absolutely stunning.
    Main advantages so far:
    Compact size & weight.
    Accepts huge charge amperage (best I can provide is around 40 amps) right up to 100% state of charge.
    High discharge loads cause little voltage drop even when battery is down to 20% state of charge.
    Hi current charging or discharging has little effect on battery life. (10 year pro rata warranty)

    The only draw back is the initial cost, but if expressed in dollars, per usable amp / hr over the life expectancy of the battery, the LiPo4 comes into its own.

    newbattery001.jpg


    newbattery004.jpg



    Cheers Chris
  • newlnewl Solar Expert Posts: 53 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    The prices are certainly out of my bracket at the moment. The number of cycles and DOD capacity is massive! Might have to sell a property just to do my full blown system properly with batteries like that. =)
  • BB.BB. Super Moderators, Administrators Posts: 29,708 admin
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Is there any Battery Manage System (cell to cell management) with your setup?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nut17nut17 Registered Users Posts: 5
    Re: Pros & Cons of Lithium-ion batteries for solar application
    BB. wrote: »
    Is there any Battery Manage System (cell to cell management) with your setup?

    -Bill

    Hi Bill, I answered this question on my "newbie" thread, but in short, I have no automated monitoring system for cell balance, but now check manually about once per month and the 4 cells are always within 0.01v, which is even better than the supplier said they would be. Cell balance is apparently no longer an issue with the latest versions of this technology.

    Cheers Chris
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    THis months home power has an article about Lithium Ions with the pros and cons. The big issue that stood out as a con was that the BMS's currently offered lack some critical features
  • BB.BB. Super Moderators, Administrators Posts: 29,708 admin
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Here is a link to the article that Peakbagger typed about (I think, don't know how long it will be available):

    https://homepower.com/articles/lithium-ion-batteries-grid-systems

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    BTW here is a chance at a Lithium Ion battery for cheap. Of course no BMS or TMS unless you can adapt the existing. Scrap the car out for parts which should cover purchase price and shipping and get your battery for free.

    http://cgi.ebay.com/ebaymotors/130826602917
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    peakbagger wrote: »
    THis months home power has an article about Lithium Ions with the pros and cons. The big issue that stood out as a con was that the BMS's currently offered lack some critical features

    The one problem which seemed the hardest to deal with is that there are currently no standard Charge Controllers which can accept an external LVD signal from the BMS, nor is there a good way to handle the situation of pack voltage dropping and/or current increasing when the BMS bypasses several full cells.
    In principle, I think that you could get a situation in which the CC is sending current full blast into a pack with all of it going through the bypasses and heating things up.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,708 admin
    Re: Pros & Cons of Lithium-ion batteries for solar application

    And from what I little I have read, the BMS setups cannot handle more than a few amps of bypassing current--If a non-integrated charger tries to continue to pump C/10 or C/5 current into the cells, the BMS will fail or or the fail safe will open (if one is present).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mtdocmtdoc Solar Expert Posts: 600 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    I'm not sure I understand the issue here. In the ebike and DIY EV (cars and motorcycle) world there are thousands of people using Lithium batteries with intergrated BMS and external chargers that do not communicate directly with the BMS -but use a constant current, constant voltage type of charge profile (basically bulk and float) without problems. Why should it be any different with a RE system?

    If there was the need to have the CC end bulk charging with an external signal - I think the Midnite Classic can be set up to do this - I believe Midnite is implementing the ability to send a logic signal into one of the Aux ports to do just that.
  • duggggdugggg Registered Users Posts: 1
    Re: Pros & Cons of Lithium-ion batteries for solar application

    My feeling is that although cell-level voltage monitoring is important, automatic balancing is not. The operating theory is, at reasonable charge and discharge currents, properly matched cells should stay in reasonable balance---and the need for manual balancing, if required, should be rare.

    I will be using a standard Morningstar TS-45 controller to charge my LiFePO4 bank. I will disable temperature compensation, float, and equalization. I will set the setpoint to 13.8 volts. And most importantly, enable the High Voltage Disconnect to occur at 13.4V and Reconnect at 13.0V---staying well away from the 2.8/4.0V endpoints where all the drama is.

    For cell-level monitoring, even a simple $20 Junsi CellLog 8 can be set to alarm if any cell is outside the 3.15-3.45V normal range---as well as fire a disconnect relay if outside 3.0-3.5V. The relay can, in turn, trip a shunt trip circuit breaker, totally isolating the battery from excessive charge or load.
  • hlim103hlim103 Registered Users Posts: 1
    Re: Pros & Cons of Lithium-ion batteries for solar application
    RCCola wrote: »
    Thanks for the response, the power router unit is exactly what I am looking for. Off the shelf inverter/charger that is compatible with 3rd party lithium ion battery systems. This one looks ideal and has the added advantage of having the mppt built in. Hopefully they will come up with a 120/240volt unit to sell in the us.

    BUMP. it has been about 9 months later and I am very interested in small batteries powering the house and appliances, ultimately using solar.

    What products have solved all the problems? What products are best?
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    nut17 wrote: »
    Hi Bill, I answered this question on my "newbie" thread, but in short, I have no automated monitoring system for cell balance, but now check manually about once per month and the 4 cells are always within 0.01v, which is even better than the supplier said they would be. Cell balance is apparently no longer an issue with the latest versions of this technology.

    I think you found out something fundamental like I did. Don't treat your house bank like you would an electric car where eeking out the last drop of capacity may cause a balance issue in the first place as you try to hypermile it home!

    I'm doing small-scale testing $$ with a low-current misapplication of Shorai Lifepo4 powersports batteries before committing to something much larger and the bms / no bms speculation goes on endlessly and so I put it to the test.

    What I discovered is this - assuming that one purchases *quality* cells that are closely matched in internal impedance to each other, (you can order them this way I believe) and stays within both the voltage charging specs, and low voltage discharge specs, the balance is extremely close - until you operate in either one of the "knees" above or below the flat charge / discharge profile. Typically this is about 80 - 10% DOD.

    I had to do some digging, but finally found a reference from Shorai stating why they don't use a bms. It is because they utilize quality matched cells, and designed the battery to be operated within the 10 - 80% DOD range on a regular basis. I have purposely taken my Shorais to the limit, and even when operated well into the knees (95% DOD to 14.8v overcharge - testing only, NOT recommended!) they are STILL relatively well balanced. Solution - don't operate at the extremes. It was only until later did I find that info from the factory and was pleased that it agreed with my own testing.

    I have the factory balance charger. And a Fluke 87V for verification, which I consider the minimum for accuracy here. I also do solar charging with my Morningstar Prostar 15 pwm. Unless I abuse it by purposely draining an individual cell via the balance port, these things stay within an acceptable balance to me even when charged via the standard two + / - terminals.

    I learned another trick - just don't charge them to 100%. Ie, just charging up to about 14.2 or so is fine, since there is very little power in the last part of the miniscule absorb - this will help to retain balance.

    Here's the real kicker - in addition to the factory charger, I like to have a backup, and picked up an Optimate TM-291 Lithium charger specifically for what it does to handle balancing which fascinated me:

    Just charge up to 14.3v, a little bit under a full charge, and repetetively cycle the voltage from about 14.1 to 14.3v - since the battery is not fully charged, this will allow those cells that are a bit low to come up on their own. Interesting! I'm doing that now on a pair of Shorais paralleled together so I can watch the balance delta over time and see how far it may diverge.

    Again, quality matters so no el-cheapo duct-tape wrapped cells here. That's been one of my biggest questions and it may have been answered by this small test setup - a bms may just be covering up poor cell quality construction, and that the answer may actually lie in producing a good quality battery in the first place, and operating it within the 80-10% DOD window.

    Stay out of the charge / discharge extreme knees, (an LVC may be handy here), use quality cells and chargers to begin with, operate within voltage specs - just like my beloved Pb batteries. By not treating my house bank like an electric car, but willingly giving up a miniscule amount of overall capacity, the whole balance issue may be overblown and just needs common sense monitoring now and then.

    Ok, just my opinion, so take that for what it's worth - which may be far less than .02C. :)
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    PNjunction wrote: »
    I had to do some digging, but finally found a reference from Shorai stating why they don't use a bms. It is because they utilize quality matched cells, and designed the battery to be operated within the 10 - 80% DOD range on a regular basis. I have purposely taken my Shorais to the limit, and even when operated well into the knees (95% DOD to 14.8v overcharge - testing only, NOT recommended!) they are STILL relatively well balanced. Solution - don't operate at the extremes. It was only until later did I find that info from the factory and was pleased that it agreed with my own testing.

    Thanks for the testing and explanation... a very informative post.

    But isn't the BMS as much a safety device as a charging system?

    Analogy: I built my solar power system utilizing quality parts and equipment. The quality is so high that I don't need fuses or circuit breakers (of course, I have them anyway).

    Isn't that what Shorai is saying... they don't need the safety of a BMS because their quality is so high?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Good point. The question is should the battery manufacturer have to build in safeguards that cover all the forms of charge / discharge abuse, or should that responsibility lay with the quality and maintenance of the bike or end user?

    My beloved Odyssey tppl agm's didn't come with a bms, and although a faulty regulator may not immediately kill it, it IS damaging the battery. So one may not notice the effect immediately, but it will catch up with you later on. Still, the fault lies with the bike, not the battery's ability to handle abuse.

    It is much like Rolls-Surrette or any other battery manufacturer demanding that one stay within specifications. To my knowledge, staying within spec is basically your bms! :)

    Actually Shorai does have a *limited* overvoltage protection (not a true bms) so that you won't suffer immediate failure as long as you don't exceed 15.2v - to the best of my knowledge. However that is NOT a green light to live with a faulty regulator. It just gives you some time to fix the problem. Wide open reg failure is not part of that plan however.

    Another manufacturer, AntiGravity doesn't use a bms. They use cylindrical A123 cells instead of prismatic, however I'm sure that they don't just grab cells from a plastic bucket and wire them together either. Unfortunately, I've seen camps on both sides basically rehash the old Odyssey flat-plate vs Optima spiral cell drama, which I've grown tired of. Choose the proper capacity and size for your application and be done with it. Toss in country-of-manfucturing drama, (usually misguided about the real facts), and the comparison with the automotive agm theater is complete. I grow tired of that drama and instead of watching, I'll buy BOTH and put them on the bench! Marketing vs reality becomes immediately apparent - both pro and con.

    I don't want to turn this into a Shorai advertisement - I just picked them since I could get them over the counter to test with. However they don't just slap random cells together, but match them at the factory prior to assembly, which is part of the labor cost. There's more to the story but I'll leave that to the bike threads.

    An additional clue to LiFepo4 battery care was demonstrated by the Optimate Lithium charger - when below 80% DOD, it applies a very low current (somewhere around 0.1C or so) until the battery reaches that stage, and then continues on with full current charging. It makes me wonder how many guys that are bottom balancing near the very limits of capacity are killing cells with an immediate application of full charge current at that low SOC? That dovetails nicely into how I revive an overdischarged Odyssey AGM with very low current and not trying to hammer them back to life - which doesn't work. Ok, different chemistry, but seems like an overall logical thing to do.

    The Optimate also compares internal resistance, so it is much smarter than just basing logic on voltage. That's something I won't be able to do when I build my larger pack, but that clue of not hammering a LiFepo4 at under 80% DOD is something I'll adopt. The best bet is not to go further than that. I'm not trying to hype Optimate, but what it does do seems so logical I'll try to emulate that.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    Just a reminder - this is not about specific manufacturers, and is only about my LiFepo4 tests with stuff I could obtain off the shelf for some hands-on as a common-man in preparation for something much larger. I really didn't want to turn it into a bike thread.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application
    PNjunction wrote: »
    What I discovered is this - assuming that one purchases *quality* cells that are closely matched in internal impedance to each other, (you can order them this way I believe) and stays within both the voltage charging specs, and low voltage discharge specs, the balance is extremely close - until you operate in either one of the "knees" above or below the flat charge / discharge profile. Typically this is about 80 - 10% DOD.

    My understanding of battery balance is that it is the balance in SOC combined with differences in storage capacity, not the difference in voltage between the cells. Any imbalance in the SOC and storage capacity of the cells will lead to a difference in the cell voltages of differing magnitude depending on how unbalanced the cells are, their SOC and the difference is storage capacity.

    If we have two perfectly matched cells with exactly the same capacity but one has a SOC of 60% and the other has 50% both will have the same cell voltage to within maybe 10 millivolts because they are in the middle of the very flat part of the charge curve but are very unbalanced. If we now charge them both slowly with 40% of their rated capacity the SOC of the cells will be 100% and 90%. At this point the cell voltages could be around 3.6 volts and 3.4 volts. If we put another 1% of charge into the cells you could get the voltages being 4.0 volts and 3.41 volts and so on. The same thing but in reverse happens if we discharge the cells.

    The balancing process is simply a case of balancing the SOC of the cells. In the above example we balance the two cells by putting 10% more charge into the second cell than the first. After balancing, if we charge them from 50% to 100% of their capacity, they could both read around 3.6 volts and we could utilise a full 100% of their capacity (not that we would) if they are in series. This process is the same as Equalising Lead Acid batteries, the only difference being that Lead Acid batteries will self balance if we push the voltage high enough to start breaking down the water in the cells into Hydrogen and Oxygen whereas LiFePO4 batteries need to have the charge imbalance dealt with externally.

    The main benefit i can see of having cells closely matched in capacity is that it means that the cell voltages will not diverge from each other over the whole range of SOC, think of the above example. I think one has to look at the extra cost and work out if it is worth it.

    Internal cell impedance matching is probably not as important in off-grid systems with the low charge and discharge current requirements compared to electric vehicles with their high charge and discharge current requirements.
    I had to do some digging, but finally found a reference from Shorai stating why they don't use a bms. It is because they utilize quality matched cells, and designed the battery to be operated within the 10 - 80% DOD range on a regular basis.

    I agree with vtmaps on this, rather like fuses and other safety equipment the BMS will hopefully just sit there and never have to do anything but ...
    As a bare minimum i would have something that monitors the voltage of the individual cells and will alarm if any go out of the comfort zone, this should be connected to something that disconnects the power source in the event of overvoltage or disconnects the load for undervoltage.
    Just charge up to 14.3v, a little bit under a full charge, and repetetively cycle the voltage from about 14.1 to 14.3v - since the battery is not fully charged, this will allow those cells that are a bit low to come up on their own. Interesting! I'm doing that now on a pair of Shorais paralleled together so I can watch the balance delta over time and see how far it may diverge.

    I can sort of see the logic in this, I would be interested in your results
    the whole balance issue may be overblown and just needs common sense monitoring now and then.

    I would agree with this, for my system I do it manually, for a friend who is not very technical I have set up an automatic system.
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    I think we're pretty much on the same page. In my off-grid low-current application, and not going into the charge-discharge extremes, I've willingly sacrificed some capacity for manufacturing / aging headroom.

    I just started my parallel Shorai testing. I have modified my 80% DOD to match what they show in their faqs - 12.866v after a rest for a static SOC determination. I plan to never go beyond that. After an initial charge with the factory balance charger on each, I've been through about 8 or so cycles in parallel and charged via the Optimate Lithium using the standard terminals only. So far no major balance problems on individual cell measurements. It's too early to tell, but It seems to be passing the infant mortality test.

    From a protection standpoint, then maybe the EarthX brand with it's built-in bms protections would be a good bike battery. Then again, from say a Shorai or Antigravity standpoint, perhaps the safety is incumbent upon the manufacturer / end user to ensure that they are operating within spec. I tend to agree with the latter, as I'm very used to staying within design parameters, and if the battery croaks due to my abuse, or application failure, I'm going to fix it from that standpoint, and not blame the battery for failing to fix / protect against external conditions beyond it's control.

    I guess the thing that will never be resolved is that some prefer a nanny internally, and others will just do what they have to do externally to make sure they are operating in a quality environment. I can see it both ways. For a BMS, it is a matter of trust to ensure that it is actually of quality manufacturing and specifications, and not really another point-of-failure in the chain.

    My biggest fear about balancing circuits is that there are many manufacturers who DO care about their product and end user and want the best, and there are others that will duct-tape their product together and include a poor-quality balancer giving them a license for shoddy manufacturing yet give them a marketing bullet-point.

    For now, I'm going the KISS route with no bms and staying within paramaters. I just feel I've got to be able to do this and understand the ramifications should I actually go with a much larger system, say made of (CALB / Winston / Sinopoly whatever) and my BMS, should I decide to use it, croaks.
  • dak664dak664 Registered Users Posts: 13
    Re: Pros & Cons of Lithium-ion batteries for solar application

    My take is not to balance, but take corrective action only when a cell drops below some low voltage alarm level.

    Li cells are kept at half charge for longest storage life so you would expect longest service life by bracketing 50% DOD on every cycle. That requires knowing beforehand the amp-hours needed, not hard for electric vehicles on a fixed route. If the typical use is 30-80% then over time unbalanced cells might go from 0-50% or 50-100%, a little harder on the lifetime of those cells but still less bad than balancing all cells at 100%

    But when one cell hits the low voltage alarm its time to bring it up again, preferably with a single cell charger, next best by shunting all the other cells during the entire charge cycle, next best by reducing charge current and shunting high cells when they reach 100%, and absolute worst by cycling a high current charger on and off, momentarily overwhelming the shunts then allowing them to bleed off excess voltage. Unfortunately most BMSs use the last method. A compromise might be to shunt at 90%, but only when the longer life is more important to the end user than a reduced capacity. And of course shunting reduces the overall coulombic efficiency.

    So oversizing a lithium ion battery is an advantage, for fixed storage anyway. Used 30kWh automotive batteries would be a good match for a nominal 10kWh storage cycle, with excess PV not being wasted on balancing.
  • mahendramahendra Solar Expert Posts: 141 ✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    I don't know if it was mentioned on this forum but i was actually doing some research on lithium batteries. I am some what convinced while lithium may be the solution to our energy storage problems there is a lot more development that needs to be don't specifically for solar/wind usage.The reason why i say so ,i was looking at some RC forums and those guys are really serious when i comes to their battery and it charge parameters.Charging parameter for lithium on a solar CC is not adequate.check out RC batteries on sites like Hobbyking.com you will see what i mean.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Pros & Cons of Lithium-ion batteries for solar application

    When it comes to charging, so are we. Development has already been established for many years, but most consumers and media don't know the difference between laptop lithium-cobalt, and much safer Lithium-Iron. Note the "iron" part. Part of the consumer holdback is that they just don't know the difference, and are scared of the word lithium. It would be much like us being scared of a "lead" battery, and not knowing that additional chemistries are either unstable, or in fact quite safe. I had friends deathly afraid of the newfangled "AGM" technology. Wouldn't touch it.

    The problem is that one has to differentiate between RC, drag bike, EV, or other motive power usage, and typical low current (relatively) house-bank solar applications. One can get easily distracted by the problems that they face.

    LiFepo4 charging is even easier than lead acid. For a 12v solar setup do this:

    * Set your charge controller to about 14.1v, even though you *can* set it up to 14.4. Don't obsess about obtaining 100% charge by mandating that current absolutely drops to zero at the end of absorb. The 14.1v setting will give you some headroom for out of balance conditions at the top end.

    * Use reasonable quality gear and batteries. Duct-tape or shrink-wrapped cells of unknown pedigree are out.

    * Low current usage (<2C, lower even better) if you start out relatively balanced, will stay that way.

    * Don't discharge past 80% DOD. That would be about 12.866v for a 12v pack, or 3.466v per cell.

    * If you need *insurance* against mishaps, then a BMS that incorporates LVC, HVC, and balancing should be looked into. If you like hands-on maintenance, and use your own LVC, then invest in a quality multimeter, something of the accuracy of a Fluke 87V or better.

    * An HVC is already covered by your controller / charger's top voltage limit.

    * Look into LiFepo4-specific controllers for more accuracy. Genasun comes to mind, although high-quality controllers with good user configurability can also be used. (For simple Morningstar controllers, the tiny Sunguard 4.5a is already at 14.1v. SunSavers on the other hand would benefit by leaving the jumper set for "sealed", which is also about 14.1 / 14.2v. No need to use the 14.4v flooded jumper removal. Here we're concentrating on voltages and ignoring the Pb chemistry silk-screening.

    * Don't use automotive trickle chargers unless you have verified their accuracy. For example, Schumacher speed chargers with their built-in high-voltage desulfation routine have boiled over some friends brand new Odyssey's and Optimas. I have tracked three different versions and didn't like what I saw. If they don't publish their voltages and charge routines, track them yourself with voltmeters and ammeters and discard them as necessary. Imagine what they'll do to a LiFepo4. But why waste time with unknowns. For small stuff, an Optimate TM291 Lithium, or perhaps the CTEK lithium charger is the much better bet than using automotive tenders especially if their performance is not known.

    * And kids, DO NOT use a typical solar panel trickle-charger that you find at the automotive parts store, or behind your windshield without using a charge controller! No ifs ands or buts here as Lifepo4 does not like the 18-20v output when directly connected and it races into the final steep charging knee. This is immediate abuse.

    * Don't cheap-out by wasting time and safety with too-good-to-be-true counterfeits or junk. Lastly, like all battery chemistries, they demand respect despite their toy-like weight.
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