12v vs 24v

andy300z
andy300z Solar Expert Posts: 39 ✭
in Solar Beginners Corner #1
hello,
I will like to know if i am using a 60amp mppt controller and (4) ,12v panels can i make my battery bank a 24 volt system and are 24v inverters more efficient that 12v . Thanks
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #2
    Re: 12v vs 24v

    Figure at least 12v increments per 1200 watts of inverter power.

    >1200 watts should be 24v
    >2400 watts should be 48v.

    The higher the voltage the lower the cabling current and therefore the smaller the required battery cables. Copper ain't cheap these days.

    I get a chuckle from these 12v 5000 watt modified sinewave inverters that are sold. They are totally absurd.

    Generally there is a slight reduction in conversion efficiency on an MPPT controller the greater the input to output voltage differential.
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #3
    Re: 12v vs 24v
    I will like to know if i am using a 60amp mppt controller and (4) ,12v panels can i make my battery bank a 24 volt system and are 24v inverters more efficient that 12v . Thanks
    As RC suggests, if you plan on growing your system above 1000 watts, then start with a 24 volt system now. This will let you grow it to about 2000+ watts and save you money.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: 12v vs 24v
    andy300z wrote: »
    hello,
    I will like to know if i am using a 60amp mppt controller and (4) ,12v panels can i make my battery bank a 24 volt system and are 24v inverters more efficient that 12v . Thanks

    simply, yes, you can make it into a 24v system given you have at least 2 12v batteries (or 4 6v batteries) to place in series and if your controller and inverter handles that voltage. the pvs themselves would be 2 in series and then parallel the 2 in series (string) with the other 2 in series (string).
    as to efficiency the inverters themselves aren't what makes a higher voltage system more efficient, but it is overcoming the resistive losses in the wires as rc touched on by being able to use a lower current for a given wattage that does it. 12v however is highly common with lots of items that can run on it directly that aren't as common with 24v. if all of your powered items are from 120vac then availability of certain voltage items does not play a part. in reality you can make your system 48v too if you have enough batteries that you could place into series. of course this depends on the controller and inverter handling 48v. your pvs would all be in series and would be fine for a 48v system.
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  • andy300z
    andy300z Solar Expert Posts: 39 ✭
    #5
    Re: 12v vs 24v

    Is it possible to hook all the panels in series which will give me a higher voltage which will give me less of a voltage drop on my 6 gauge wire which the panels are 80 feet from the charge controller. appx 68v @ 5amps.
    It look like no matter how the panels are hooked up the wattage is the same. it seems you have to figure out which works better on your wire distance.
    Also wouldnt the mppt contoller take that high voltage and bring down to lets say 26 v to properly charge the batteries.
    Which is better for charging a battery 68v @ 5 amps or 34v @ 10amps ?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: 12v vs 24v
    andy300z wrote: »
    Is it possible to hook all the panels in series which will give me a higher voltage which will give me less of a voltage drop on my 6 gauge wire which the panels are 80 feet from the charge controller. appx 68v @ 5amps.

    Yes. So long as the Voc doesn't exceed the input maximum on the charge controller (and be aware that cold temps will increase the Voc).
    It look like no matter how the panels are hooked up the wattage is the same. it seems you have to figure out which works better on your wire distance.

    That's correct; Wattage remains the same, no matter how you divide it up into Volts & Amps.
    Also wouldn't the mppt controller take that high voltage and bring down to lets say 26 v to properly charge the batteries.

    Yes; that's one advantage of MPPT. Proper charging Voltage for a "24 Volt" system is more like 28.4, btw.
    Which is better for charging a battery 68v @ 5 amps or 34v @ 10amps ?

    It's not quite that simple. The input to the MPPT is not relevant for battery charging; it's the output that matters. There you need to achieve the proper charging Voltage and current for your battery bank. You should try to achieve a peak current of around 10% of the batteries' Amp hour rating @ the proper charge Voltage. As in: a 12 Volt 100 Amp hour battery "wants" 14.2 Volts @ 10 Amps = 142 Watts (derated; about 178 Watts really). Just an example: your actual numbers will vary.
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  • andy300z
    andy300z Solar Expert Posts: 39 ✭
    #7
    Re: 12v vs 24v

    Thanks. This thing is getting addictive!!!!
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: 12v vs 24v

    If you have no need to source 12vdc, go with 24vdc. That said, there are many items that we use off grid that are 12vdc, telephone, stereo, some lighting, as well as lighter chargers for other things like Ipods/camera batteries/laptops etc.

    It is much easier to convert 12vdc to 24 vdc for specific loads, (Like my water pump) than it is to convert 24 to 12.
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