Which is better A/H or Volts 12 vs 24

moorsb
moorsb Solar Expert Posts: 38 ✭
in General Solar Power Topics #1
It looks like it cheaper to build 24 vdc system than a 12 vdc. Is it a trade off?
The higher cost of batteries for 24 vdc, need 2x more 6v batteries for the same A/H. Is the cost of more batteries offset by the lower cost of wire.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Which is better A/H or Volts 12 vs 24

    my comments in bold.
    moorsb wrote: »
    It looks like it cheaper to build 24 vdc system than a 12 vdc. Is it a trade off?

    that would all depend on what you are doing and with what. on the surface anything upgraded to the 24v system from 12v will see a reduction of the current to 1/2 in keeping with the same wattage. you may find the need for less wire an advantage, but some of the items to be run may cost more if on 24vdc power. in other words the 24v fan or light is more specialized and not as common and may cost more. if all loads are off a 24v inverter then it may boil down to the wire savings which will not be great in the the big scheme of things as battery and inverter costs will be similar in both.

    The higher cost of batteries for 24 vdc, need 2x more 6v batteries for the same A/H. Is the cost of more batteries offset by the lower cost of wire.

    this depends on the capacities involved and battery varieties available as well as how your setup is. if the original 12v system consists of a only 1 12v battery then yes i agree it could cost more even if the batteries bought are are now to be 1/2 of the ah as you would need to purchase twice as many batteries at 1/2 the capacity. in 12v systems that have more than 1 battery in parallel then it could be a matter of just rearranging the batteries. for example, 2 100ah batteries in parallel for 12v for could just be seriesed for 24v and no extra costs are needed. you are not losing any power in that example because when the ah down by a factor of 2, the voltage went up by a factor of 2 as that power is determined by both the amperage and voltage being multiplied together.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Which is better A/H or Volts 12 vs 24
    moorsb wrote: »
    It looks like it cheaper to build 24 vdc system than a 12 vdc. Is it a trade off?
    The higher cost of batteries for 24 vdc, need 2x more 6v batteries for the same A/H. Is the cost of more batteries offset by the lower cost of wire.

    Battery cost is the same, once you get to the point where you need more than one battery. There are many 3 & 4 parallel battery, 12V systems that would cost the same as hooking them into series, for 24 or 48V. As you get to the higher input voltage inverters, you can't get small ones. (there is no 300W 48V inverter that I know of) and so your inverter cost can be much higher.
    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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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
    Re: Which is better A/H or Volts 12 vs 24

    In general terms, net power (watts used) are the same if they come from 12 vdc or 24 or 120 volts. There are some small efficiency differences between systems, but the net/net is probably exactly the same. Depending on the number of batteries, the number of battery connections may have more cable connections in a 24v volt system than a 12 volt one. (May not though!)

    Remember VxA= Watts

    So same number of batteries, (lets say 4 225 T-105 6 volts)

    4 @ 12 volts would yield about ~450 ah or ~5400 wh (225x2. 2 strings of 2 batteries each)

    4@ 24 volts would yield ~ 225 ah or ~5400 wh! (225x1 1 string of 4 6volts)

    So in the net/net it really doesn't make much difference. The advantage of a 24 (or larger) system is the ability to use smaller wire gauges in you wiring AND have less wiring loss in the system, possibly adding a bit to system performance.

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Which is better A/H or Volts 12 vs 24

    Most often the reason for going with a higher DC Voltage is the need for greater Watts in AC output. The higher Voltage reduces the DC current and lessens the complications that are a result thereof (Voltage loss to resistance, heat generation, et cetera).

    You have to think about the over-all usage; is there any need for 12 V DC sub-systems? Is there a need for consistently high Wattage? (Over 1000, say). That would be either by a single device or several things used concurrently.

    Personally, if you're going to consistently use more than 1000 Watts it's worth considering 24 V. But if you only "peak" at less than 2000 from time to time, I'd stick with 12 V. Remember the higher Voltage system needs higher Voltage array as well. That too can put costs up.
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  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    #6
    Re: Which is better A/H or Volts 12 vs 24

    for me I regret going 12 volt because 1200 watts of panels is about all a flexmax 80 will handle @12 volts, if I want to add panels I'll need to get another charge controller, if I had a 48 volt inverter, I wouldn't need to add another cc until I passed 5000 watts of panels
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #7
    Re: Which is better A/H or Volts 12 vs 24

    Reguardless of which you choose, buy any 12 volt nominal panels in pairs so if you decide to go with a higher voltage system later you can run them in series.
    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.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Which is better A/H or Volts 12 vs 24
    Photowhit wrote: »
    Reguardless of which you choose, buy any 12 volt nominal panels in pairs so if you decide to go with a higher voltage system later you can run them in series.

    Unless you're going to use an MPPT controller, in which case array Voltage is not dependent on system Voltage.

    I started with an MX60 controller for just this reason. It has allowed me to reconfigure both system and array Voltage without having to buy a new controller.
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #9
    Re: Which is better A/H or Volts 12 vs 24

    For anything battery-backed, I hate to say "always go with 12 or 24 volt nominal panels", but, yeah -- stay away from the high voltage panels made for bipolar and HVDC systems.

    I was looking at some very sweet SunPower WHT 315's recently for a client and two in a string was all an FM-80 could accept. Kyocera has (along with other vendors, but I'm sweet on Kyocera) panels that can be strung much higher than 630 watts per series.

    In the 12 / 24 / 48 (or in between) decision, peak load and bank configuration for required storage are what I use to figure out which way to go.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: Which is better A/H or Volts 12 vs 24
    Photowhit wrote: »
    Reguardless of which you choose, buy any 12 volt nominal panels in pairs so if you decide to go with a higher voltage system later you can run them in series.

    in addition you may find some other vendors may insist upon the pairs because of extra packing when being shipped it could cost you more.
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #11
    Re: Which is better A/H or Volts 12 vs 24
    niel wrote: »
    in addition you may find some other vendors may insist upon the pairs because of extra packing when being shipped it could cost you more.

    They usually come in pairs when they are palletized. Breaking a pair is more labor because each singleton then has to be repackaged when shipped.
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