Battery QTY

seantseant Registered Users Posts: 9 ✭✭
I’m about to purchase new batteries and am going back and forth between 8 and 12 or going from 24 volt to a 48 volt system 

I currently am at 24 volts and have a small mighty max bank.   

When I plug my volt meter in/ turn all lights and TVs/boxes/we boost/ my draw sits 320/340.  It will spike if my DC water pump comes on 

outside I have 8 265 watt Kyocera panels

and a midnight solar 150 CC

at my elevation in Central Washington,March/Oct, I see 5/8 hours of sun a day 

I don’t leave my inverter on, at the most Monday thru Friday, we may use it for 3 to 4 hours in the evening .  Weekends up to 10 hours

My question is, will 8 Rolls Surret L16 380 amp hour batteries be enough.  I’m looking for 2 days on no sun without charging 

I’m aware I will probably have buy 2 more panels 

reasons why I don’t want to switch to 48 volts

new step down,  new charger, and new inverter

thanks for the help

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,909 ✭✭✭✭✭
    You are looking for a balanced system. I'd suggest with 10 - 265 watt panels 8 -380 ah batteries (a bank of 760 ah at 24 volts) would be about right. Certainly wouldn't want to go to 12.

    Generally you would want your array to be able to provide 10-13% of your batteries capacity. A 10 panel made up of 265 watt Kyocera panels would typically provide 2650 watts÷ 24 volt charging = 110 amps, but in normal situations when hot they will only produce 75-80% of that or around 88 amps about right for 760 ah battery bank.

    You can look at your Normal Operating Cell Temperature values on your info sheet, these may be your panels;

    https://www.solar-electric.com/lib/wind-sun/KU265-6MCA.pdf

    What size battery bank are you replacing/have you had in the past?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    edited March 2020 #3
    You are getting close to the "break point" for choosing 48 volt over 24 volt battery bank... If you are not planning on a larger battery bank down the road (more loads in the future), and your existing system meets your needs (heavy enough wiring for 24 volt bank, enough battery bank to supply your present loads), then changing is probably to 48 volts may not be worth it.

    If (when) your AC inverter fails, you may wish to thing about 48 VDC AC inverter and rewiring your batteries into a 48 VDC bank.

    My suggestion is that when you battery bank needs gets over ~800 AH (i.e., 800 AH @ 24 volts), it usually makes sense to go for the next higher voltage battery bank (i.e, 400 AH @ 48 volts). Reducing the wiring size/voltage drop at high currents (i.e., 80 amps @ 24 volts vs 40 amps @ 48 volts).

    Obviously, there is an advantage to 24 volts if you want to "fractionally" increase battery bank capacity... 8 vs 12 batteries (6 volts) gives you a 50% increase of bank capacity. With 48 volts, you only have the 8 vs 16 battery choice (same battery AH capacity) and a 100% (doubling) of battery bank capacity (doubling of solar array suggested, etc.). 2x large battery bank step (at 48 volts), may be more than you wish (2-3x 24 volt strings, vs 1-2 string step @ 48 volt bank).

    Note: I messed up the following. Got confused between 8x batteries @ 24 volts and wired for @ 48 volts. Will correct the following equation for 4x series x 2x parallel strings or 24 volts @ 760 AH (same storage as 380 AH @ 48 volts).
    Is an 8x 380 AH @ 6 volt batteries system, 2 days storage, 50% discharge with 340 Watt load:
    • 24 volts * 2 parallel string * 380 AH bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge (for longer battery life) = 3,876 Watt*Hours per day
    • 3,876 WH per day (ideal storage for 2 days) / 340 Watt average load = 11.4 hours of load support per day (at 340 Watt average loads)
    Does appear to be a relatively good match for your needs... Does it seem to meet your expectations?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • seantseant Registered Users Posts: 9 ✭✭
    edited March 2020 #4
    I ordered the 8. And will start putting the 48 volt stuff on order.  Would these batteries strung at 48 provide me with more power vs 24 volts? 

    Ordered the surret 487 AH L16s 
  • PhotowhitPhotowhit Solar Expert Posts: 5,909 ✭✭✭✭✭
    seant said:
    Would these batteries strung at 48 provide me with more power vs 24 volts? 
    There won't be 'more power' Power is measured in watts.

    The basic equation is Watts = Amps x Volts

    In series the voltage adds, but the amperage remains the same.
    In Parallel the amperage adds and the voltage remains the same.

    So if you change the configuration from 760 amps at 24 volts to 380 amps at 48 volt you end up with the same power/wattage of  24x760=18,240watthours and 48x380=18,240 watthours.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.BB. Super Moderators, Administrators Posts: 32,804 admin
    Seant,

    Please note, I bunged the above post #3. I corrected it to show 8 batteries @ 6 volts @ 380 AH per battery. You can wire them either as 24 volts @ 760 AH (4x series for 24 volts times 2 parallel strings for 760 AH)... Or you can wire them as 48 volts @ 389 AH (8x batteries in series for 48 volts @ 380 AH).

    The theoretical answer about which bank will supply more energy (i.e., battery capacity in Watt*Hours)--Both are identical.

    The theoretical answer regarding which bank will supply the most power (Watts or highest peak/average load draw)--Again, the batteries are still 8x organized differently, but will have pretty much the same performance... So no difference there.

    Then there is the universe of practical answers... First, to get (say) 10% current draw on the banks, one bank will be 760 Amps * 10% = 76 Amp draw. The other would be 10% * 380 AH bank = 38 Amp draw.

    2x the current, means 2x heavier wiring (more $$$ copper), and potentially more charge controllers... Typical larger charge controllers are rated for 60-90 amps or so... So, if you had a 10% rate of charge for a 24 volt @ 760 AH bank , then you would need 2x 60 Amp charge controllers (@ 76 amp rate of charge), or a larger 80 Amp+ solar charge controller.

    So, from a hardware design point of view, there are cost adders for running a large (I suggest >~800 AH) battery bank at 24 volts vs a 400 AH bank at 48 volts.

    So, if you plan on a 13%+ rate of charge at 24 volts (760 AH) vs 48 volts (380 AH):
    • 760 AH bank * 0.13 rate of charge = 98.8 amps (very few solar charge controllers at ~100+ amps, need 2x 50+ Amp solar charge controllers)
    • 380 AH bank * 0.13 rate of charge = 49.4 Amps (lots of solar controllers in the 60-80+ Amp range)
    And you have to look for your inverter (or inverter+charger). It used to be difficult to find any "smaller" 48 VDC inverters (smaller than ~4,000+ Watts). So, getting a 24 volt "smaller" AC inverter (or inverter+charger) may have been a better choice (1/2 wattage 24 volt inverter is ~1/2 the price of the larger 48 volt inverter). Larger inverters generally have higher "tare losses"--Basically a smaller inverter may take 20 Watts "just turned on". A larger inverter may take 40 Watts "just turned on". If you run your inverters 24 hours per day (common for larger systems), the energy cost of the larger inverter could be something like:
    • 40 Watts * 24 hours per day = 960 Watt*Hours per day
    Almost as much energy per day that a full size refrigerator consumes per day (typically 1,000 to 1,500 WH per day for an energy star efficient fridge).

    So, knowing your load requirements (do you need a 500 Watt AC inverter, or a 5,000 Watt inverter, any "surge loads"--Typically AC induction motors/well pumps/etc.) is job #1.

    Then start going through and find AC inverters (or inverter-chargers--Combined AC inverter and 120/240 VAC genset supported DC Battery charging function) that meet your needs and bus voltage (get price).

    Your max loads (DC and AC inverter input), and your maximum charging current (whichever is higher), define your wiring/battery bus current, size of fuses/circuit breakers, and even supported length of wiring (you can send more power longer distances at 48 VDC vs 24 VDC or 12 VDC).

    There is no one "right answer" that one of us can give you... It all depends on your power needs, price points, do you want fancy stuff (like bluetooth/Internet monitoring/backup genset/etc.)... Do you want 2x 60 Amp charge controllers, or 1x 80 amp controller (or 2x 80 amp, etc.).

    I suggest you look around at the various inverters and charge controllers to get an idea of what's out there (our host, who started/pays for our little forum here is: https://www.solar-electric.com/ out of Flagstaff Az). You can also look at Ebay/others too for some possibly less expensive options--No problem for us.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 1,753 ✭✭✭✭✭
    BB. said:

    I suggest you look around at the various inverters and charge controllers to get an idea of what's out there (our host, who started/pays for our little forum here is: https://www.solar-electric.com/ out of Flagstaff Az). You can also look at Ebay/others too for some possibly less expensive options--No problem for us.

    -Bill
    Less expensive maybe for some of the lower quality lesser known brands. I've found NAWS has very competitive pricing on all the quality products they sell. They really don't offer the junk brands so you can rest assured your purchase from them will be a quality product.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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