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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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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 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.
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.
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 :-)
