lithium battery capabilities

mahendra
mahendra Solar Expert Posts: 188 ✭✭✭
in General Solar Power Topics #1
Ok i would really like an experienced professional to chime into what i am going to ask here.I think i may be over doing it but i have to clarify.
For a period of time i have been researching on lithium batteries for off grid storage and i have came across something repeatedly and that is the capability for lithium to accept very high charge rates (based on c20 /other ) and also discharge ratings e.g c5/c10 etc

Now my question

If lithium are capable of such higher charge and discharge rates as compared to lead chemistry is it possible to run larger constant loads as of those recommended for lead acid batteries? i.e no load beyond 1000w for 12v systems /no load beyond 4000w for 48v systems.
So say can i run like say 6000w loads on 48v system with out hurting the battery assuming i have the wiring and over current devices for such system?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: lithium battery capabilities

    The current load limit in respect to system Voltage has nothing to do with battery type. It has to do with the outright Amperage pulled for a given amount of Watts output.

    You can use loads above 1000 Watts on a 12 Volt system and loads above 4000 Watts for 48 Volt systems. I don't know where you got those numbers from.

    Instead look at it based on current handling for system Voltage. 4/0 AWG wire can handle 300 Amps. On 12 Volts that's 3600 Watts. On 48 Volts that's 14,400 Watts. Providing the battery bank has the capacity to provide that much current (total current; conversion efficiency and inverter consumption included) it would work with either type of battery. But I don't think you'd want to press any wire to that sort of limit for a continuous load.

    The higher charge/discharge rates of both AGM and Lithium means you can come closer to those max rates for a given Amp hour capacity.
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #3
    Re: lithium battery capabilities
    mahendra wrote: »
    For a period of time i have been researching on lithium batteries for off grid storage and i have came across something repeatedly and that is the capability for lithium to accept very high charge rates (based on c20 /other ) and also discharge ratings e.g c5/c10 etc
    SOME LiFePO4 batteries (lithium iron phosphate) batteries can accept those charge rates. No lithium ion battery that I know of can accept them. (And of course primary lithium cannot.)
    If lithium are capable of such higher charge and discharge rates as compared to lead chemistry is it possible to run larger constant loads as of those recommended for lead acid batteries? i.e no load beyond 1000w for 12v systems /no load beyond 4000w for 48v systems.
    Not really. You have two problems:
    1) Voltage sag caused by internal battery resistance. LiFePO4 batteries may help with this.
    2) Voltage sag caused by resistance in wiring/protection/inverter. Batteries will not help with this.

    With very good (i.e. low internal resistance) batteries you may be able to reduce the amp-hour rating of your battery bank below inverter manufacturer's recommendations. But you still need to be able to supply the energy and power needed, and your wiring/protection has to handle the current without excessive losses.
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #4
    Re: lithium battery capabilities

    well honestly speaking i have a 12v system that is efficient but not adequate for my usage and i normally run load above 1000w on this system .
    The reason i am asking this question is because i was told on an earlier post right here on this forum that it is not wise to run continuous load of a certain amount on the mentioned systems,since it is not good for the batteries regardless if the wiring and capacity of the batteries were above recommendations.
    So second question since my concern is with 48v systems -

    What is a realistic maximum battery bank and load can i have designed for a 48 volt system. I am looking for around an 8000w or 10000w system that can run efficiently and safely
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: lithium battery capabilities
    mahendra wrote: »
    well honestly speaking i have a 12v system that is efficient but not adequate for my usage and i normally run load above 1000w on this system .
    The reason i am asking this question is because i was told on an earlier post right here on this forum that it is not wise to run continuous load of a certain amount on the mentioned systems,since it is not good for the batteries regardless if the wiring and capacity of the batteries were above recommendations.
    So second question since my concern is with 48v systems -

    What is a realistic maximum battery bank and load can i have designed for a 48 volt system. I am looking for around an 8000w or 10000w system that can run efficiently and safely

    Outback Radian is an 8kW 48 Volt inverter. At that power level it will pull about 186 Amps (at 48 Volts; less with the system at higher Voltage). If you need greater output than that you would need to parallel a couple of these or XW6048's et cetera. Then each inverter would have its own wires.

    But they would all draw from a common battery bank. That bank at 10kW AC output would be delivering approximately 232 Amps. Wit standard flooded cells you would need at least 2,320 Amp hours (10% draw). With AGM's you could technically draw 20%, but the quantity of power over a given amount of time remains the same. As such trying to use a smaller AGM battery bank means you will deplete it faster because of the higher current rate. In other words you reach the 50% DOD mark sooner.

    Some flooded cells such as forklift batteries, certain lithium batteries, and some other technologies like NiFe can take deeper than 50% DOD.

    So you have to look at all three aspects: Amp hour capacity, DOD maximum, and discharge rate.
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