12, 24 or 48 volt

[Prickley]

Hi I m new to this forum and to solar power
I have a bit of basic knowledge but would like to ask the question:

Lets say i want to install a 5kw inverter and and use 8 batteries of 12v 100ah for arguments sake
what is the best voltage to look at to make the most use out of the capacity of the battries?

Tel me if im wrong or right:
12 volt sustem i will have 800ah
24 volt system i will have 400ah
and on a 48 volt system 200ah

which wll be the best to feed such an inverter

Thank you in advance

[Sunking]

Highest voltage is always the best solution as it is the most efficient which saves you money on installation and operational cost. But your example is a very poor example because a 5 Kw inverter screams 48 volts and you cannot run a 5 Kw inverter on 8 12 volt batteries of 100 AH as that would only make a 48 volt battery at 200 AH. Minimum battery requirement is 48 volt @ 800 AH and a minimum panel wattage of 4000 watts with a 80 amp MPPT charge controller. You would never use 12 volt batteries for such a system. You would use 2 or 4 volt 800 AH batteries all wired in series. You gotta get out of the 12 volt box you are trapped in.

There are some general rule of thumbs, and is why we can easily spot problem without thinking or a thought.

Inverter Wattage roughly equals Panel Wattage is the first test to pass.

0 to 1000 watts can be 12 volts
0 to 2000 watts can be 24 volt
0 to 4000 watts can be 48 volts

Why you ask? Because the largest MPPT Charge Controller you can buy is 80 amps. A 80 amp CC has the follwing maximum power input vs battery voltage.

1000 watts @ 12 volt battery
2000 watts @ 24 volt battery
4000 watts @ 48 volt battery.

So as you can see you can run any panel wattage you want at 48 volts up to 4000 watts. Go lower in voltage and you have tighter restrictions. It is about what you need balanced with economics. You would not run a 12 volt battery system with 200 watt panel and 80 Amp MPPT controller because the 80 amp controller cost $600. You can buy a 200 watt panel and 20 amp mppt controller for less than $600.

Everything has to match up or you let the magic smoke out of the box, or empty your wallet.

[sensij]

Tel me if im wrong or right:
12 volt sustem i will have 800ah = 9600 Wh
24 volt system i will have 400ah = 9600 Wh
and on a 48 volt system 200ah = 9600 Wh

5000 W / 12 V = 417 A
5000 W / 24 V = 208 A
5000 W / 48 V = 104 A

Use 48 V.

For arguments sake, that doesn't sound like much battery to support loads that would require such a big inverter.

[Prickley]

Thanks guys
This is why i joined the form of knowledgeables.

So what size inverter would you suggest for a monthly usage of roughly 600KWh?
If my calculations are correct i would need about 1700wh per day averaged, keep in mind where i am, utility power is 220 volt

[thastinger]

Thanks guys
This is why i joined the form of knowledgeables.

So what size inverter would you suggest for a monthly usage of roughly 600KWh?
If my calculations are correct i would need about 1700wh per day averaged, keep in mind where i am, utility power is 220 volt

1.7x31 does not equal 600

[SunEagle]

1.7x31 does not equal 600

Correct. If he uses 600kWh a month then his consumption is closer to 20kWh / day. That would require a pretty big solar/battery system.

[Sunking]

Thanks guys
This is why i joined the form of knowledgeables.

So what size inverter would you suggest for a monthly usage of roughly 600KWh?
If my calculations are correct i would need about 1700wh per day averaged, keep in mind where i am, utility power is 220 volt

You are joking right? I don't think you have any idea what you are asking for. I will give you the short answer you will fully understand and become crystal clear to you.

To generate 18 Kwh per day or 600 Kwh per month will initially it will cost you $40,000 to $50,000 depending on location. Then every 5 years $20,000 to $25,000 in battery replacement cost.

Clear enough?

[Living Large]

Thanks guys
This is why i joined the form of knowledgeables.

So what size inverter would you suggest for a monthly usage of roughly 600KWh?
If my calculations are correct i would need about 1700wh per day averaged, keep in mind where i am, utility power is 220 volt

I am going out on a limb, and suggesting that you meant to say "roughly 60 kWH a month." Roughly 2 kWH a day.

[Sunking]

I am going out on a limb, and suggesting that you meant to say "roughly 60 kWH a month." Roughly 2 kWH a day.

Its all in the details. Silly decimal points and zeros.

Doesn't change my answer. Just shift the decimal point accordingly.

[paulcheung]

Correct. If he uses 600kWh a month then his consumption is closer to 20kWh / day. That would require a pretty big solar/battery system.

That is my daily consumption, I have 6920 watt solar panels, 750amp hours battery at 48 volts, 2 charge controller 80 and 60 amps. Magnum MS4448PAE inverter with grid and generator backup. Cost me $25,000 US Dollars one and half years ago with 16 4000 series Rolls 6 volts batteries. Any day I got rain or heavy overcast I have to use generator or the grid to charge the batteries.

[SunEagle]

That is my daily consumption, I have 6920 watt solar panels, 750amp hours battery at 48 volts, 2 charge controller 80 and 60 amps. Magnum MS4448PAE inverter with grid and generator backup. Cost me $25,000 US Dollars one and half years ago with 16 4000 series Rolls 6 volts batteries. Any day I got rain or heavy overcast I have to use generator or the grid to charge the batteries.

Well I would classify a 7kw of panels and a 48v 750Ah battery system pretty big and not cheap. Glad it is working out for you.

I want to make sure the OP has stated his correct usage. It is either 20kWh or 1.7kWh per day. Big difference when sizing your system hardware.

[Prickley]

Sorry guys i typed it out all wrong, it was friday afternoon at work

I use between 400 and 600Kwh per month
Giving an average of 20Kwh per day
I worked on a 12 hour average (instead of a 24hour average since usage isnt constant troughout the day) that is where i got the 1.7Kw per hour from.

Sorry my mistake saying it was 1.7Kwh per day

[SunEagle]

Sorry guys i typed it out all wrong, it was friday afternoon at work

I use between 400 and 600Kwh per month
Giving an average of 20Kwh per day
I worked on a 12 hour average (instead of a 24hour average since usage isnt constant troughout the day) that is where i got the 1.7Kw per hour from.

Sorry my mistake saying it was 1.7Kwh per day

Glad you got the math straightened out. As you can see in an earlier post by paulcheung he uses about 20kWh per day and his system is larger than what you have planned. It might cost you as much as that $25,000 he paid or more.

What ever you decide to do a 48volt battery system is the only way to go.

[Living Large]

Sorry guys i typed it out all wrong, it was friday afternoon at work

I use between 400 and 600Kwh per month
Giving an average of 20Kwh per day
I worked on a 12 hour average (instead of a 24hour average since usage isnt constant troughout the day) that is where i got the 1.7Kw per hour from.

Sorry my mistake saying it was 1.7Kwh per day

Maybe I am wrong, but I am not sure enough details have been given yet unless those in the know, know them without being stated.

Is this on-grid or off-grid? You asked about using 8-100 Ah batteries. At 48V, you would have 200 Ah, or 9600 Wh. If you use 1.7kW per hour, you would have only 3 hours of usable storage. Is this a backup for a grid-tied system? Sorry if this newbie (me) is off base...

EDIT Dereck pointed out earlier you need at least 800 Ah for a 48V 5kW inverter.

[Prickley]

Thanks guys, 48v it is then, i used the 8 batteries as an example as that is what i am able to afford at this stage, i allready spent about R20000(ZA currency) on what i have and that doesnt include an inverter, a decent sinewave inverter will cost me about another R25000