batteries needed

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Have 1100 watts solar power, on a 12 volt system, batteries need replacing, would it be beneficial to go 24 volt system and how many batteries would be needed.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: batteries needed

    that depends on exactly what you're going 24v with, just the pvs or both the pvs and the batteries. keeping the batteries at 12v and feeding with a 24v or higher pv system through a downconverting mppt controller will allow you to keep your 12v loads like lights or inverters while reducing resistive losses through the pv wires. switching to a 24v battery bank as i supposed you to mean means changing your loads to suit as you won't be able to use a 12v light or inverter on a 24v battery bank. if you planned on changing inverters and such other loads to 24v anyway then a 24v battery bank will have the benefits of reducing losses through a higher voltage there too.
    now as to the number of batteries in a 24v system, that would depend on what each of your battery's base voltage is. if it's 6v then 4 in series is needed and if 12v batteries there will be 2 in series. to get the proper current you will parallel more of these series strings of 24v batteries until the needed ah rating is attained. most times the same number of batteries will be used provided it is an even number of batteries. if you presently have an odd number of batteries you may need to add 1 additional 12v battery or 2 6v batteries to allow for the last 24v battery string to be formed for paralleling. this often means that doubling the voltage allows you to have half of the ah rating needed as the wattage would be identical.
    hope you followed this without my confusing you.
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  • TnAndy
    TnAndy Solar Expert Posts: 249 ✭✭
    #3
    Re: batteries needed

    "would it be beneficial to go 24 volt system"

    Maybe....mabye not. Too little info provided for an answer.

    Will your charge controller adjust to 24v ? Are you using an inverter ? Is it 12v and would have to be replaced if you reconfigure the battery bank ?

    "and how many batteries would be needed"

    Depends on what you're doing with them......but at a minimum, 2-12v, or 3-8v, or 4-6v or 12-2v........
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: batteries needed

    The singular reason to go with 24 volts is to reduce wiring losses by raising system voltage. After that, the choice of battery voltage is largely related to how and why you are going to use them. If you are running 12vdc load like auto/truck/rv hardware then staying with 12vdc makes sense. If you are going to invert to 120/240vac then it really doesn't make much difference except for wire size.

    The biggest question is how much hardware you are willing to change our with your batteries,,, charge controllers, chargers, inverters, appliances etc.

    Tony
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,893 ✭✭✭✭✭✭
    #5
    Re: batteries needed

    I often design between 24V and 48V. Besides wiring the reason for 24V offgrid is all the appliances/equipment that can run directly off 24V. For smaller systems it is the way to go. It can save thousands of dollars.

    48V is where my user has a big budget and has less of a concern about phantom loads, wall warts, and all the small losses.

    12V battery systems are from the old days! If you have them and are happy with them why change? Why did your battery fail? Are you offgrid?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
    Re: batteries needed

    David,

    Just out of curiosity, what 24vdc appliances are you referring to? It has always been my impression that 12 vdc units are more readilly available due to the
    RV market.

    Tony
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: batteries needed
    SEMOsolarstore wrote: »
    I've been told that a 24 volt DC system more efficiently inverts into 120 AC than does a 12 volt DC system doing the same thing.

    I think someone is telling you stories ! The little Moningstar SureSine 12 - 120V inverter is about the most efficient one anywhere. A little bit of engineering got nearly all the sine inverters (grid tie & stand alone) into the 93% ballpark, regardless of input voltage.
    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 ,

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,893 ✭✭✭✭✭✭
    #8
    Re: batteries needed

    David,

    Just out of curiosity, what 24vdc appliances are you referring to? It has always been my impression that 12 vdc units are more readilly available due to the
    RV market.

    Tony


    OK here is my List for small to medium home.

    24V DC freezer and refrigerator, current favorite is the Stecca
    24V El Sid solar hot water pumps
    24V Wattsun solar tracker power
    24V outdoor fluorescant lighting
    24V 1mA system voltmeter
    24V attic fan
    24V evaporative coolers
    24V Shureflo Extreme Sensor fresh water pumps
    0V Crystal cold 18cu ft propane
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
    Re: batteries needed

    David,

    Thanks. I had thought of pumps,, and in fact I run my shurflo on 24vdc with a voltage doubler from 12vdc. .

    Tony
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