Proposed Battery Bank

northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
I have been considering using Aquion's AHI batteries after my current set of lead acid batteries expire. I am also aware that one of the main issues with the AHI battery is that they have relatively high internal resistance and considerable voltage range. There could also be an issue with voltage sag under loads, kicking out the inverter prematurely. I see that in another system, they have set it up in such a way that the generator will come on line, when significant loads appear at the same time the battery SOC is relative low. It sounds like they are using the generator to handle the voltage sag of the AHI bank, at a lower SOC with loads.

I am seriously considering going the AHI route, and was thinking of going with a slightly smaller AHI stack quantity than originally planned. To deal with voltage sag, I would put in place a small LiFePo4 pack, that is set up to engage (ie put in parallel) with the AHI pack, thus, boosting the voltage and preventing the inverter from prematurely kicking out at lower SOC's.

For example, I would install say qty 10, S20 stacks into a 48 volt bank. This equates to roughly 20kwh of storage. If voltage of this pack under load drops below an adjustable preset level, I would engage the LiFePo4 pack, which would be sized to handle sub C currents with typical loads that come on. For handling a 3 to 4 kw load, a relatively small 100 ah pack @ 48 volts would suffice. The LiFePo4 pack would only engage when the load is present, and disengage shortly after. The relay used to connect the LFP pack to the main bank could also double as your LVD. And the relay for charging the LFP pack could double as your HVD, where charging could be redirected to the main pack from a separate smaller CC and panel setup.

I think that the two chemistry's could do very well together. Maybe it was meant to be? embarrassed.gif The only concern I have is it may be desirable when cutting in the LFP bank to do it softly rather than full on?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Assuming the AHI batteries have fairly high resistance/low surge capabiliities--I would think that you would need a "two or three source" AC inverter... AHI battery, LiFePO4 battery, + genset.

    The bad thing about AHI in parallel with LI is that AHI has a very wide output (and probably input) voltage range--Whereas the LI has a very narrow voltage range. Pure parallel would mean that the LI would sink/source a large amount of current when in parallel with an AHI bank--With the only "limit" being the fact that the AHI has high resistance--High enough to "safely" parallel with a LI voltage source? Don't know that answer.

    The simplest would be to have diode isolation for each battery bank... That way, neither battery could be recharged by the other--And if the AHI "nominal operating voltage" is higher than the LI -- The LI would then be the "floor" for surge current support... But of course, each battery bank would need its own charging source (and may need its own charging source).

    The only way I can think of making a possible AHI+LI AC power source from off the self hardware... Starting with the AC load:

    1. connect the AC load to a XW/Outback inverter with AC support. The inverter operates in "pass through" normally, and if AC power exceeds programmed input limit, this Inverter goes into "AC support" mode. This buffers AC surge with LI battery bank.

    2. Connect the first AC inverter to a second AC inverter upstream. This second AC inverter would have the AHI battery bank. Its output current is rated for continuous use, and low to no surge current.

    Connect the #2 AC inverter to your small genset. Connect #1 inverter to your "large" genset for very large AC loads/emergency backup.

    Of course, each battery bank has its own AC charger (inverter-charger). And you would need separate solar battery charger for each battery bank. Or use Inverter #2+solar to recharge Inverter #1 with solar power via AC interconnect from upstream #2 inverter + solar + small AC genset..

    With multiple inverters, you have increased losses (conversion losses/charging losses)--But the #1 inverter should not use that much Watt*Hours because it is for surge support--So it is possible that the extra conversion losses are less of an issue (20%-30% extra losses * a small(er) amount of WH is still a small amount).

    Anyway--That is my first pass of thinking about a "versatile" AHI+LI system and attempting to keep over all battery costs low (AH for WH, LI for Watt Peak, don't need to "oversize" AHI bank for surge).

    Whether or not a 2x larger AHI bank would cost more than second AC inverter + smaller LI bank--Not sure...

    Longer term--If AHI become popular (or to help them become popular)--An inverter with dual battery input/support (AHI+LI) would seem to be reasonably possible. Perhaps funded by AHI folks to increase market share.

    My first thoughts on the AHI+LI questions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    Bill, I think it could be done with just one inverter. I'm thinking that the only time the LFP bank will normally be engaged (ie paralleled with the AHI pack) is under 2 conditions. One is when a substantial load is detected. The other is when the AHI battery pack falls below an adjustable preset level. This will be acting like a boost and will prevent the inverter from kicking out prematurely under load. Also, because the Ir of the LFP pack is so low, when it is engaged, it will take on the majority of the load, There may be some current flow as well from the higher voltage LFP pack to the lower voltage AHI pack, but I don't think it would be substantial due to the relatively high Ir of the AHI pack, and the fact that the voltage of the AHI pack will rise higher, as the LFP pack takes the load. And besides it wouldn't hurt to provide a little extra charging to the relatively low SOC state of the AHI pack.

    The extra solar charging circuit for the LFP pack would be relatively small and once the charging of the LFP pack is complete, the panels could be switched over to the main AHI charging network (using a relay).

    Charging the LFP pack by generator through the inverter could also be done, but thinking it may be easier using the small MPPT solar charger. (ie tapping in to the generator output, rectifying it, and feed in to the MPPT). That way you can easily control charging using the generator.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,838 ✭✭✭✭✭
    I think if you really feel this way go ahead and test this for us! Short of that, have you ever tried operating with a single string lead acid battery system. It often solves alot of problems offgrid!
    Good Luck
    northerner wrote: »
    Bill, I think it could be done with just one inverter. I'm thinking that the only time the LFP bank will normally be engaged (ie paralleled with the AHI pack) is under 2 conditions. One is when a substantial load is detected. The other is when the AHI battery pack falls below an adjustable preset level. This will be acting like a boost and will prevent the inverter from kicking out prematurely under load. Also, because the Ir of the LFP pack is so low, when it is engaged, it will take on the majority of the load, There may be some current flow as well from the higher voltage LFP pack to the lower voltage AHI pack, but I don't think it would be substantial due to the relatively high Ir of the AHI pack, and the fact that the voltage of the AHI pack will rise higher, as the LFP pack takes the load. And besides it wouldn't hurt to provide a little extra charging to the relatively low SOC state of the AHI pack.

    The extra solar charging circuit for the LFP pack would be relatively small and once the charging of the LFP pack is complete, the panels could be switched over to the main AHI charging network (using a relay).

    Charging the LFP pack by generator through the inverter could also be done, but thinking it may be easier using the small MPPT solar charger. (ie tapping in to the generator output, rectifying it, and feed in to the MPPT). That way you can easily control charging using the generator.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    High current DC relays can be expensive. And if you don't have latching relays, you will be pulling something like 6 watts per relay while "on".

    Also, if you use diodes--Running somewhere around 0.2 to 1.0 volts drop (depending on diode type and current flow)... 200 amps * 1 volt = 200 Watts--Lots of heat sinking required.

    Lastly, the more complex the system is, the more wild and wonderful ways it can fail (relay welds a contact, Diode fails shorted or open, etc.).

    Be really careful--You are dealing with substantial DC Voltages (upwards of 60 VDC) and possibly insane levels of available current in the event of a short circuit/dead short/switching AHI+Li at the "wrong time/voltage levels".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    I think if you really feel this way go ahead and test this for us! Short of that, have you ever tried operating with a single string lead acid battery system. It often solves alot of problems offgrid!
    Good Luck

    Dave, I'm looking at getting away from lead acid batteries. Still contemplating the route I will take, but AHI may prove out really well in the long run. They do have drawbacks, however, and just looking at them.
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    BB. wrote: »
    High current DC relays can be expensive. And if you don't have latching relays, you will be pulling something like 6 watts per relay while "on".

    Also, if you use diodes--Running somewhere around 0.2 to 1.0 volts drop (depending on diode type and current flow)... 200 amps * 1 volt = 200 Watts--Lots of heat sinking required.

    Lastly, the more complex the system is, the more wild and wonderful ways it can fail (relay welds a contact, Diode fails shorted or open, etc.).

    Be really careful--You are dealing with substantial DC Voltages (upwards of 60 VDC) and possibly insane levels of available current in the event of a short circuit/dead short/switching AHI+Li at the "wrong time/voltage levels".

    -Bill

    Bill, I am aware of the cost and issues with high current relays. I wouldn't consider using diodes, as I don't think they would be necessary. I know that LiFePo4 systems often use a relay as a LVD, so It would be along those lines. The advantage of the relays I would use, is they would normally be open, and would only draw current occasionally when a load comes on at low SOC. I was also thinking about using a soft start, ie a 2nd relay that would employ a large resistor temporarily before the direct line is engaged. It could also be used for the disconnect procedure. The soft start would reduce the amount of sudden current transfer.

    Not sure how bad the voltage sag issue is with AHI, but it is the only major drawback that I see with these batteries. They have the potential of very long cycle life,
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Another approach would be to use the AHI battery as bulk storage, have a charger that charges the LFP battery from the AHI battery and have the inverter running exclusively off the LFP battery.

    With the equipment you already have, you could set up two 24 volt AHI batteries each being charged by one of your CCs. These would be hooked up in series to make a 48 volt battery. You would need a 48 volt to 24 volt charger and BMS, with enough output to supply your average power requirements over a 24 hour period to charge the 24 volt LFP battery. You might be able to use a small MPPT solar controller to do this job. The size of the LFP battery would have to be enough so the maximum load from your inverter is around 2C. Your thoughts of a 100Ah LFP battery would be about right for your inverter. The inverter would be connected to the LFP battery. You would use your current generator to charge the LFP battery or supply power for your loads or both when the LFP battery is empty.

    Another option for 48 volt systems would be for two 48 volt AHI batteries giving a combined output of 96 volts. This 96 volts DC should be usable with a large number of standard switch mode 110 volt AC battery chargers.

    Unless the price of the AHI batteries has come down since I last looked I can't see that they work out cheaper than using just LFP batteries.

    Simon
    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
     

  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    karrak wrote: »
    Another approach would be to use the AHI battery as bulk storage, have a charger that charges the LFP battery from the AHI battery and have the inverter running exclusively off the LFP battery.

    Thanks for the suggestion karrak and that would be another way of going about it. The main issue I see is that you would have yet another efficiency drop running all your bulk storage energy through the charger.

    Another method would be to create a small 48 volt LFP bank as previously mentioned, but feed this through the Midnite Classic that would send charging current to the main (24 v) bank when needed, but again you would lose some efficiency from the small bank.

    Yet another method is having 2 separate inverters (I think Bill alluded to this method) and tie them in on the AC side through a transformer. The inverter on the LFP side would normally be in sleep mode until tasked with a heavier load. Of course that would mean buying a second inverter.

    I still like the original plan, however, need to look at just how much current the AHI bank could draw from the LFP bank? If significant, then would be a no go for that approach.
    Unless the price of the AHI batteries has come down since I last looked I can't see that they work out cheaper than using just LFP batteries.

    Not sure what you pay in Australia for both types of batteries, but I figured out that price of the AHI based on "cycle life" is actually cheaper now than LFP in NA, and price of AHI is expected to drop. Of course actually battery life is highly speculative at this point, but I don't plan to wait 20 or 30 years to find out! I have read that Aquion will drop the price from about $500 US /kwh now, to about $350 US /kwh by the end of this year, and eventually down to $200 US /kwh..8)
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    Thought about this some more and figure that running a small LFP bank through a charge controller such as the Classic, in order to "boost" the AHI battery might be the best approach. The CC could also double to charge the LFP bank during the day when the sun is out.

    There would be a slight efficiency loss going through the CC, but at least one could limit current flow out of the LFP battery. Question though, how much higher would the LFP battery voltage be above the AHI bank, in order for the mppt charger to work efficiently? I'm sure one or two extra cells should be enough to raise LFP voltage enough. Using a battery for charging supply is not the same as using solar panels. The LFP battery will have a relatively fixed voltage, but very high current capability. Thoughts?
  • mike95490mike95490 Solar Expert Posts: 8,466 ✭✭✭✭✭
    You need more than 5V, but less than 3x the battery full voltage. Above 3x battery voltage, you get a lot of loss in the MPPT, 2x battery voltage is a good point.
    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 ,

  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    mike95490 wrote: »
    You need more than 5V, but less than 3x the battery full voltage. Above 3x battery voltage, you get a lot of loss in the MPPT, 2x battery voltage is a good point.


    Not sure if you can switch battery bank voltages without manual input with the Midnite Classic (ie between 24 and 48 volts)? 5 volts should be doable I would think. One or perhaps 2 extra LFP cells should do it?

    The other option would be to put in dedicated PWM charge controllers. One for charging the LFP pack and either one or two for boosting the AHI pack. Will have to check out various models to see if one can limit current flow through a PWM charge controller to preset levels?
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    northerner wrote: »
    The main issue I see is that you would have yet another efficiency drop running all your bulk storage energy through the charger.

    This is not necessarily true. During the day when there is input from the solar panels, the power to charge the LFP battery would come via the main charge controller, bypassing the AHI battery. The only inefficiency would be that the power to charge the LFP battery would go through two charge controllers. MPPT controllers should be more than 95% efficient so this is not a large loss.

    The arrangement outlined in my previous post could actually be far more efficient as we would only ever be drawing power from the AHI battery at a very low rate which increases the overall efficiency of the AHI battery. We could also set things up so that the LFP battery is charged during the day and only charged from the inefficient AHI battery when there is not enough sun and the LFP battery gets below say 20-30% SOC. With some thought you might be able to setup a standard MPPT controller to do this.

    Simon

    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
     

  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    karrak wrote: »
    The arrangement outlined in my previous post could actually be far more efficient as we would only ever be drawing power from the AHI battery at a very low rate which increases the overall efficiency of the AHI battery. We could also set things up so that the LFP battery is charged during the day and only charged from the inefficient AHI battery when there is not enough sun and the LFP battery gets below say 20-30% SOC. With some thought you might be able to setup a standard MPPT controller to do this.

    Simon

    Simon, I think your suggestion could work efficiently, however, you would be asking a relatively small battery size to handle a lot of cycling. I was thinking of having just enough LFP battery to handle the power demands, and only when needed, so was thinking of a relatively small battery for that. Also one would be putting a lot of dependence on maintaining a balanced LFP battery. If it was the other way around, the LFP battery would only be there to assist when needed, and if something did go astray, you wouldn't be faced with a system shut down. I'm thinking that the AHI battery will give a good overall cost advantage, and thus think it is best placed center stage. We just pray that cycle life works out in practice.

    I think your idea could work well, but depends on system demands and one's focus.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    northerner wrote: »
    you would be asking a relatively small battery size to handle a lot of cycling. I was thinking of having just enough LFP battery to handle the power demands, and only when needed, so was thinking of a relatively small battery for that.

    LFP batteries have been made to handle lots of cycling. From my understanding calendar ageing is as large a factor in the life of an LFP battery as wear through cycling. I think it is more than likely that you will get say ten years of use cycling an LFP battery around 60% daily and the same life span cycling say 30% daily.
    Also one would be putting a lot of dependence on maintaining a balanced LFP battery.

    From my experience over nearly two years with an LFP battery, I think maintaining a balanced LFP battery is a non issue.
    If it was the other way around, the LFP battery would only be there to assist when needed, and if something did go astray, you wouldn't be faced with a system shut down. I'm thinking that the AHI battery will give a good overall cost advantage, and thus think it is best placed center stage.

    I think that doing it this way around not only adds to the complexity, but also means that you are not making use of one of the main benefits of LFP batteries, being the overall efficiency of >95%, which could be used to counter the poor efficiency of the AHI batteries.

    Simon

    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
     

  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    karrak wrote: »
    LFP batteries have been made to handle lots of cycling. From my understanding calendar ageing is as large a factor in the life of an LFP battery as wear through cycling. I think it is more than likely that you will get say ten years of use cycling an LFP battery around 60% daily and the same life span cycling say 30% daily.
    Simon

    If I had a small LFP pack in place, I would likely be looking at deep cycling on a daily or perhaps even twice daily in winter basis. The rating of 2000 cycles to 80% only works out to a little over 5 years life. I guess one could put in a larger LFP battery, to compensate.
    From my experience over nearly two years with an LFP battery, I think maintaining a balanced LFP battery is a non issue.

    It could be more of an issue with a small LFP battery as it is seeing heavier usage to deeper depths of discharge. My concern is that a cell imbalance could shut down the system when I'm not home. If that happens in winter, my place could freeze up.
    I think that doing it this way around not only adds to the complexity, but also means that you are not making use of one of the main benefits of LFP batteries, being the overall efficiency of >95%, which could be used to counter the poor efficiency of the AHI batteries.

    The biggest expense with batteries is replacement cost, and I'm placing my bets on AHI for overall cost performance. That's why I'm thinking of putting the AHI center stage, to handle the majority of the cycling.

    The difference in efficiency would only be about 10% or less, particularly if one limited heavy current flow from the AHI battery. That could be countered by adding one or two extra solar panels in my case. It appears that the efficiency of the AHI is similar to the flooded lead acid batteries I have now, so I wouldn't see much change there. I'm more concerned about saving on cycling life than on efficiency, for overall economy of operation.

    As for the complexity, It could be done using 2 relays (actually make that 3 relays, another one to switch the extra panels over to the others), a voltage detection circuit, and a current (load detection) circuit. Not really that complex, and a failure with the LFP system wouldn't impact my power system.
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    northerner wrote: »
    I would likely be looking at deep cycling on a daily or perhaps even twice daily in winter basis. The rating of 2000 cycles to 80% only works out to a little over 5 years life.

    If the Winston/Balqon documentation can be believed, and there are some glaring inconsistencies in their documentation, 60% cycles should get you around 10 years use.
    My concern is that a cell imbalance could shut down the system when I'm not home. If that happens in winter, my place could freeze up.

    The only times you notice any problems with balancing under normal circumstances is if you charge the LFP cells to more than 3.5volts/cell (SOC > ~95%) or discharge to less than 3.2 volts/cell (SOC < ~20%). As long as you make sure your battery is balanced when it is commissioned and keep an eye on any variation in cell voltages over a timescale of months you shouldn't have any problems. If you do have a problem with cell imbalance when charging all you have to do is stop charging and let the battery SOC drop until the cell voltage imbalance disappears. At the other end when the battery is at a low SOC, all you have to do is disconnect the load and put some charge into the battery until the cell voltage imbalance disappears then you can reconnect the load. You do not have to disconnect the battery until there has been manual intervention.

    My main concern with your arrangement and I think Bill touched on this is what happens if there is a fault/software glitch that leaves the relay that connects the two batteries together turned on, or turns it on at the wrong time. You will need to make sure that this can't cause any problems.

    May I ask what voltage/number of cells you intend to run the LFP battery at.

    Simon

    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
     

  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    karrak wrote: »
    My main concern with your arrangement and I think Bill touched on this is what happens if there is a fault/software glitch that leaves the relay that connects the two batteries together turned on, or turns it on at the wrong time. You will need to make sure that this can't cause any problems.

    May I ask what voltage/number of cells you intend to run the LFP battery at.

    Simon

    Maybe I didn't make it very clear, but I won't be connecting the two batteries together directly. I was planning to run the current from the the LFP battery pack through an MPPT charge controller to provide isolation and limit current flow between the 2 banks. If I used the Midnite Classic, and stayed at 24 volts, would give me about a 2000 watt boost to the AHI bank. If I switched to 48 volts, which I'm contemplating, that boost would be close to double that. The majority of my heavy loads max out somewhere between 2 and 3 kW, so even a 2 kw boost would be significant.

    Mike mentioned that I need about a +5 volt differential between the battery source and destination, in order for the MPPT to work. So if I stay at 24 volts, I would split the AHI stacks in two to give me a nominal 24 volt pack. For the AHI pack, I would go with one extra cell for a total of 9 cells and about 200 ah each. 9 cells at 3.2 volts each equals a 28.8 volt pack. If the 28.8 volt potential is not quite enough, it may require a 10th cell? If I do switch to 48 volt system, then a 100 ah LFP pack should be sufficient.

    So if the AHI pack had a voltage drop due to load below about 22 or 22.5 volts, and a significant load is detected, the system would trigger a relay to provide current to the MPPT CC, and feed it down to the AHI pack. This is the boost to compensate for the heavy load when the AHI pack is somewhere in the range of 20 to 50% SOC, thus extending the usable range, and preventing the inverter from kicking out.
  • northernernortherner Solar Expert Posts: 492 ✭✭✭✭✭✭
    karrak wrote: »

    LFP batteries have been made to handle lots of cycling. From my understanding calendar ageing is as large a factor in the life of an LFP battery as wear through cycling. I think it is more than likely that you will get say ten years of use cycling an LFP battery around 60% daily and the same life span cycling say 30% daily.
    Simon

    That's one of the main concerns I have with LFP. From what I'm hearing there may be a limited calendar life, but of course it's too early to say for sure? And with a battery bank, the emphasis is on the amount of storage (ie in order to make it through at least 2 or 3 days, in order to minimize generator run time.) So if one sizes the bank for adequate storage with LFP, cycle life may be well in excess of actual calendar life. In other words, if one sizes an LFP bank for an average daily discharge of 35% for example, the cycle life rating is about 7000 cycles, which works out to nearly 20 years if cycled once daily. Actual calendar life of the battery is likely considerably less than that, but of course remains to be seen.

    Thinking now that I may be able to get by with an even smaller boost battery, and thus the additional cost won't be quite so much. A 100 ah battery at 24 volts could still put out a considerable boost at about 0.5c. One would be extending the usable capacity of the main bank, which makes it worthwhile IMO.
  • westbranchwestbranch Solar Expert Posts: 5,163 ✭✭✭✭
    Here is a very interesting lady, who was involved with the design and construction of the Volts battery bank and more... introducing a new battery technology... the second link gives a lot of background info

    https://www.youtube.com/watch?v=sovRU7-bya8
    https://www.youtube.com/watch?v=_60SIyoZBOQ
    http://sakti3.com/?page_id=50
    https://www.youtube.com/watch?v=sv21Q7fcq3A
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • westbranchwestbranch Solar Expert Posts: 5,163 ✭✭✭✭
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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