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Searching on internet i've found some articles like this : https://earthship360.com/what-is-the-advantage-of-a-24v-system-over-a-12v-system/ that is in favor of higher voltage system.

But on other articles , i've read that is better 12V or there's no significant differencies.

So , Is there any advantage choosing one or other system ? Thank you !

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    Higher voltages are used for running cable over long distances (transmission lines). But no real advantages. – Josh Jobin Mar 20 '16 at 18:55
  • @Josh Jobin According to that article , what about 1) Better input regulation and 2)Better inverter efficiency and regulation ? – Ferdi Mar 20 '16 at 19:02
  • Really depends on the inverter. Do you have inverters in mind? – Josh Jobin Mar 20 '16 at 19:04
  • ok , what do you think about this 24V inverter : powerwalker.com/?page=product&item=10120209&lang=en – Ferdi Mar 20 '16 at 19:08
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    That earthship360 article appears to be written by a knowledgeable industry professional. Everything in there seems to be accurate. The point about line regulation is that if you lose 1V in a 24V system, that is a small loss (on a percent basis) compared to a 1V loss in a 12V system. – mkeith Mar 20 '16 at 20:16
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As the inverter power level goes up, 12V inverters become totally impractical due to the required wire diameter. For example, if you have a 4kW inverter, it would be really ridiculous to design it for 12V. 4kW/12V = 433A. Even at 1kW, you are pushing limits with a 12V inverter.

There are a lot of really junky inverters out there. If you see a high power inverter that takes 12V, there is a good chance that it is a piece of junk, and that the ratings are wildly optimistic.

For off grid home use, I would recommend you work with the highest battery voltage that is practical (which is generally 48V). This will allow you to use more reasonable wire diameters without power loss. Power loss in wire is a function of I squared, so it makes a big difference. And copper is expensive. And fat cables are difficult to work with. Etc.

If you can't or don't want to work with 48V, then 24V is the next best thing.

  • The wire size makes a big difference, I have only set up a few solar systems but 48v was the best option, I would use the highest voltage your array can support.+ – Ed Beal Jun 24 '18 at 18:56
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The 24 volt system might be a little more efficient, but the emphasis is on the word little. It's a little bit easier to design for smaller currents, but 2x difference isn't that much after all. Real efficiency benefits would be gained from having a 400 VDC (or something around that - not really sure what the exact voltage should be) system, which would eliminate the need for a step-up stage in power inverters.

12 volts, on the other hand, has the advantage that there's a lot of equipment that can run directly from 12 volts. Stuff like cellphone car chargers, lighting equipment, car televisions etc. And 12 volt equipment such as inverters for example are generally more common and thus cheaper than their 24 volt counterparts. The boost in efficiency in using 12 volt equipment comes from not having to step up and invert the voltage from 12 volts to 110 or 230 volts before being able to use the equipment. You can run lights, watch TV, charge your cellphone and even use a laptop computer without switching on the power inverter.

Possibly dangerous hint regarding laptops here: Many laptops with 18 volt input can be run directly from 12 volts (that happens to be the voltage of their internal batteries). I'm successfully running a couple of low end laptops, for example HP 530 this way at a summer cottage PV system. The laptop constantly shows a systray battery icon, not charging and the charge level stuck at 60%. I don't recommend that you try this with a new or good laptop since I can't guarantee that it won't break up or explode, but you may want to see if you can use your old laptop this way.

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There are two issues. A) the inverter itself and B) the cables to connect it to the batteries.

The Inverter

Other things being equal, I would expect the 24v inverter to have a slight efficiency advantage over 12v. This is due to a wider range of FETs being available that will handle the higher voltages, and lower currents in the supply wires. But the difference will be small, and could easily be exceeded by any particular differences of a particular model and manufacturer.

A 12v inverter may well have worse regulation than 124V, though need not have, it depends how much copper has been put in to carry the current. There will always be the temptation to skimp, which will do less harm on a 24v input than 12v.

The Supply

If you want to run the inverter at any distance from the batteries, the difference between (say) 70A at 24v and 140A at 12v will be quite significant. Don't forget double the current will need 4x the copper area for the same power loss in the cables, and fractional regulation at the inverter.

For a fixed system, 24v is the obvious preference over 12v, as it requires less copper to supply it. If you want to be mobile, then you may want to choose 12v for use from a single car battery. If you have the option, then it's worth looking at 48v, less supply copper again.

  • Actually , i want to use with pairs of car batteries , never from a car.According to article , what about 1) Better input regulation and 2)Better inverter efficiency and regulation ? – Ferdi Mar 20 '16 at 19:02
  • Thank you for your answer. But please can you explain to me the problems with wires ? Because the batteries are almost in the same place with inverter (20cm distance ) , and in the output both inverters produce 220V. So for what wires are you speaking ? – Ferdi Mar 20 '16 at 22:53
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One thing that should be noted, is that it depends somewhat on the grid voltage in your country. In America, where the grid voltage is around 110VAC, your conversion ration is about 1:10. In Europe and in Africa, where we use 230VAC, that ratio is a lot larger, and 24V or even 48V inverters are favoured. Efficiency is usually better for the lower ratios, but as the other answers have noted already, it is only a little better.

The main problem remains the size of your cables. 12V is simply unworkable for anything above about a kilowatt. 24V is good up to about 3 kilowatt, and for anything above that you want 48V.

Cable size isn't the only problem. Parallel battery strings also come with drawbacks, not so much on discharge, but particularly on recharge. If the strings aren't perfectly balanced, one string overcharges while the other(s) is undercharged and dies of sulfation: The worst of both worlds. With a single string, you're limited to maybe 1000Ah. At a C5 rate, that's 200 Ampere, which is around 2.5kw. In other words, high power levels on a 12V system are impossible without parallel strings.

I personally own a 24V Victron Multiplus. I picked 24V for my system as it strikes a good balance between the aforementioned cabling requirements, and the amount of equipment you have to buy. With a 48V system, you have to buy everything in multiples of four. With a 24V system, you buy in multiples of two, which is often much easier on the pocket.

I hope that helps :-)

  • Thank you for your answer. But please can you explain to me the problems with wires ? Because the batteries are almost in the same place with inverter (20cm distance ) , and in the output both inverters produce 220V. So for what wires are you speaking ? – Ferdi Mar 20 '16 at 22:58
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    I think we are all talking about the required wire diameter for the DC side of the inverter. The current will be half in a 24V inverter compared to a 12V inverter. And that can make a big difference in terms of required fuse and wire diameter. For example, 600 Watts = 50A at 12V, but only 25A at 24V (at 100% efficiency). For 50A, you might need #6AWG wire, but for 25A, you might need #10AWG. The #6AWG is a lot more difficult to deal with. – mkeith Mar 21 '16 at 0:51
  • If you are talking for the wires between batteries and inverter , these are wires less than 1 meter. We can get wires with needed diameter , and i don't think we have to spend much more money for just 0.5 meter cable. – Ferdi Mar 21 '16 at 1:55
  • What is the maximum sustained DC current in the wire? What wire gauge do you plan to use? You should calculate the voltage drop in the wire under sustained load conditions. If you end up using large diameter cables to avoid voltage drop, they can be more difficult to terminate or require special tools. That is the only drawback I can see. But make sure you go through the calculations. You definitely are going to need something larger than #12AWG. – mkeith Mar 21 '16 at 4:05
  • I have 35mm square cables on my 24V 1.6KVA inverter. That is one size oversized, but it is good to oversize to compensate for low battery voltage conditions when current goes even higher. Largest cable you can buy at the local hardware store is around 50mm square. This is on 24V, sized for peaks of 3kw (my inverter can handle that). Now imagine having to double the size of that cable for your 12V inverter :-) – izak Mar 21 '16 at 10:06

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