How many Kwh does my battery bank system have?

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fisherus
fisherus Registered Users Posts: 3 ✭
in Off Grid Solar & Battery Systems #1
I need some clarification to see if I configured my battery bank system correctly. I have 15 Toshiba SCiB LTO 64.8V 45AMP batteries wired parallel. Currently, I am using a Sol-Ark 12k set at 60V Nominal and 48V Minimal. By having the batteries in parallel, I am assuming that I have a total of 675AMPS in my bank. To configure the total Kwh of my battery bank system do I multiply the total amount of AMPS by the nominal figure of 60V (which is the maximum amount they will be charged) or by the maximum amount of the battery capacity of 64.8V? 
Presently I have 16 360W panels in two paralleled series of 8 panels going into one charger and a series of 8 370W panels going into the second charger. This is a total of 8720W of maximum solar per maximum sun hour, averaging 3.7 hours per day. I have a water heater and small hot tub connected to use the overages of power being produced with a switching system that I can redirect the power to my well pump to fill my 2500 gallon storage tank. 
Can someone please advise me what the total capacity of my battery bank system is in Kwh?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Fisherus,

    Can you give a link to your battery pack/bank/configuration? Something like this?

    https://www.scib.jp/en/product/module/2p12s.htm
    https://www.sol-ark.com/sol-ark-12k/

    You are talking about having batteries in parallel--But is it the Toshiba or the Sol-Ark bank you are asking about?

    And the normal rules, batteries connected in series string "add voltage".

    Batteries (strings) connected in parallel "add capacity / Amp*Hours".

    Going with the basic equations:
    • Power  (rate of energy usage) = Voltage * Current
    • Energy (storage) = Voltage * Current * Time (Hours in our case)
    A 200 AH @ 6 Volt Golf Cart battery:
    • 200 AH * 6 volts = 1,200 Watt*Hours of storage (simple look)
    And the same physical size of 12 volt lead acid battery would have similar Watt*Hour capacity:
    • 100 AH * 12 volts = 1,200 Watt*Hours of storage
    And the conversion from Watt*Hours to kiloWatt*Hours is the 1/1,000 factor (kilo):
    • 1,200 WH = 1.2 kWH
    The details are that batteries at "full" have a higher voltage vs discharged batteries... A typical 48 VDC inverter will run from 42 Volts (battery cutoff for Lead Acid type) to 50.8 volts (full/resting voltage).

    Rate of discharge, your actual battery operating voltages (for example, one of Li Ion battery systems runs from ~60 volts to 40 volts (full to empty). The 40 volts is below most AC inverter's cutoff voltage.

    And many batteries will run more charge/discharge cycles (and not age as fast) if you run from 90% State of charge to 20% state of charge (less cycling range, longer cycle life).

    So the energy equation values can depend on temperature, state of charge, how fast of discharge (high current causes battery and wiring voltage drop), what the beginning and ending voltages are, and how deeply you cycle the battery...

    Simple is to take the voltage at the middle of the range, and the AH capacity at the rated discharge rate (C/100, C/20, C/10, C/5, etc.)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Mike_in_PA
    Mike_in_PA Registered Users Posts: 12 ✭✭
    edited April 2021 #3
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    If you have the 45 amp  unit shown here: https://www.global.toshiba/ww/products-solutions/battery/scib/product/module/2p12s.html then that is 45 amp in the 27.6 volt nominal configuration, where there are two strings of 12 cells in parallel 2p12s, but you have them in 1p24s so that is 22.5 amps at 55.2 volts nominal, or ~ 1.2 kwh per unit.  Then  15 of those would give you ~ 18 kwh of LTO storage.

    Have you had a chance to operate the system?  How are the units behaving in parallel?
    48 GEPV-110, 2 SMA 2500U, 7 AE32s since 2004 
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