12, 24 or 48

VivienVivien Registered Users Posts: 6
We're trying to understand the difference between 12, 24 or 48 v systems. We use about 300 kw per month and are planning to purchase solar panels with battery back-up. We hear conflicting things about which way to go with this. Any advice? Thank you so much,



  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12, 24 or 48

    The choice of system Voltage is based mainly on how much power you use. The more Watt hours per day, the better off you are going up in system Voltage rather than increase the Amp hour capacity of the battery bank. This is to keep the current manageable.

    For instance, using the 10% peak charge rate and a 60 Amp controller you get numbers like this:
    12 Volt system, 600 Amp hours of battery = 3600 Watt hours maximum
    24 Volt system, 600 Amp hours of battery = 7200 Watt hours maximum
    48 Volt system, 600 Amp hours of battery = 14,400 Watt hours maximum

    To try to store 14,400 Watt hours of capacity on a 12 Volt system would require a 2400 Amp hour battery bank. That would want a charge rate of 240 Amps, which would require four 60 Amp controllers (or three 80 Amp ones).

    The other factor is the maximum power. If you need to supply 1200 Watts peak or less, a 12 Volt system can handle that. But as the maximum peak Wattage goes up so does the Amperage, and a 12 Volt system starts to get unmanageable current levels when you pass the 2 kW mark.

    Does that make it any clearer?
  • RCinFLARCinFLA Solar Expert Posts: 1,482 ✭✭✭✭
    Re: 12, 24 or 48

    The voltage of the battery system is based on your peak power requirements. Average kHW will not determine if you can start or run your peak loads.

    For example, if you have to start a house pump that requires a 4kW inverter to supply the starting current surge then you should go with a 48 v system.

    You could use a 24 vdc system but it would require larger wire gauge for battery cabling and possibly more stress on batteries. If you have no other devices or total peak loads then just the one short duty cycle pump then maybe a 24 vdc system is okay. Personally I would go with 48v.

    General, a good rule of thumb is 12v increments for every 1000 to 1200 watt increment in require peak power.

    kWH requirements will determine the capacity requriements on the batteries.
  • petertearaipetertearai Solar Expert Posts: 471 ✭✭✭✭
    Re: 12, 24 or 48

    Definatly not 12volts.
    Go for 24 or 48
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: 12, 24 or 48

    One difference is that batteries in series are easier to keep equally charged than are batteries in parallel. If you have 4 12V batteries, it's easier to keep them happy in series (@48V) than in parallel (@12V), even though you have the same number of Watt-hours available.

    Another difference is that high voltage low amperage systems can use smaller (less expensive) wiring than low voltage high amperage systems because conductor ampacity is independent of voltage.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 12, 24 or 48

    as the advantages of higher voltage have been explained you might then say why aren't all systems going to the highest voltage they can all of the time? it's pretty simple in that when one would go to expand in capacity, be it pvs or batteries, that you don't want to do it in higher numbered increments. for instance to expand the 48v battery bank would mean 4 12v batteries or 8 6v batteries rather than 1 or 2 for a 12v battery bank or twice that for a 24v battery bank. same goes for pvs too as a series string being added is more expensive than say 1 pv being added. it could also be battery weight or physical size constraints or even that the loads require a certain voltage.

    to summarize this, it's a juggling game between the best system physically and electrically for the costs. what voltage to go to has to be weighed and concidered and there could be more factors to consider than i have listed and can vary from one install to another, not to mention from one owner's preference to another. there are some cases that there isn't much choice too.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: 12, 24 or 48

    And there are times when 12 Volt is preferable. Small cabins and mobile applications like RV/campers. There you can get a lot of 12 Volt stuff off the shelf from the automotive world which makes set-up and maintenance easier. But it does put some practical limitations on the available power.
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