12V or 24V for Home solar system?

by Alex

Hi how are you. Is it better to use a 24volt solar system for your home over a 12 volt. thank u

MEG: Graeme says 24V has advantages: The higher the voltage, the less voltage drop you get on cabling. This saves you losing voltage over a long cable from panels to converter.

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Aug 02, 2016
Replying Eugene,
by: Chris

A battery cell is 1.5 volts and a combination makes up a "battery", 8 cells= 12V, 16= 24v etc. When they are connected together they form battery bank.
A 100AH 12v battery will supply 100Amps for 1 Hour,
2 x 100AH batteries connected in parrallel will supply 200Amps @ 12volts

2 x 100AH Batteries connected in series will give 100Amps @ 24Volts (Battery1+ --> Battery2- the output will be Battery1- and battery2+ -||+-||+

A 48V system then would be 2 x 24v in series or 4x 12V batteries connected together in series. -||+-||+-||+-||+ or 16x 400AH 3Volt.

Hope this helps

Jun 15, 2016
by: Eugene

"Instead of buying a battery which has a capacity of 1000AH at 12V, (12KWH) you rearrange the battery as a 24V 500AH (12KWH)"

Can you please explain this? How do you rearrange a 12v battery?

May 15, 2016
Cable sizes and Battery Voltage
by: Tony Clark

Ohms Law is used to calculate the current from power, or the voltage drop in a cable, or other parameters.
P=V*I Where P = Power, V = Voltage and I = Current
This can also be written as P=VSq/R (Vsq = V*V) or P=ISq*R
Also, V=IR or I=V/R or R=V/I

If you have a 100W load at 12V you will draw about 8A. If it is at 24V, 4A or 48V, 2A.

A 100W load is small as far as Stand Alone Power Systems. In our home we have a 4.2KVA inverter and a 48V battery. At full load, the inverter will draw over 88A (Inverter losses will increase this)
If my battery cables have a resistance of 0.01 Ohm, then the voltage drop will be 88
*0.01=0.88V This is not a major issue at 48V as this is only a small fraction of the battery voltage, but if you tried to supply this power from a 24V battery, the current would be 196A and the voltage drop would be 1.96V or 8% of the battery voltage.
At 12V, the current would be 384A giving a voltage drop of 3.84V which is 32% of the battery voltage.

How to overcome this?
* Use a higher battery voltage (replace inverter to allow use of a higher voltage battery) or
* Increase the cable size to reduce the resistance of the battery cables.

Would a higher battery voltage cost more?
No, The total power in the battery will be the same. Instead of buying a battery which has a capacity of 1000AH at 12V, (12KWH) you rearrange the battery as a 24V 500AH (12KWH) or 48V 250AH (12KWH). The total power available from the battery is exactly the same, but with lower losses in the cabling and inverter.

I am happy to assist in further explanations, if needed. Tony

Jan 25, 2016
RV systems
by: Anonymous

Will all of this hold true in an RV system as well? Using a 24v or a 48v to charge 12v or 24v batteries? Cable losses are very low.

Jul 31, 2015
by: Anonymous

Responding to the question:
"If I use 12V battery and my load is 100watt, which size of wire I have to use?"

That depends on how far your load is from the battery. 100 watts @ 240 volts is just over 8 amps, DC power does not like traveling very far so to answer that question you will need to post a little more info on what your running and how far it is from the batteries.

If your running a 100watt inverter you need to allow for the inverters peak load which will be greater than 100 watts. But really need to know what your running and how far from the batteries is the load.

Jul 30, 2015
wire size
by: Anonymous

If I use 12V battery and my load is 100watt, which size of wire I have to use?

Mar 31, 2015
24 volt solar panels can I use ?
by: Anonymous

I have 2x250 watt solar panels( 24 volt). I have already setup a solar system with 12 volt luminous invertor , 12 volt 150 ah luminous battery and one number of solar panels 74watt and another 85 watt. and run.

Now may i use 250x2 solar panel in this system or otherwise

Please help me.

Jun 01, 2014
Losses in low voltage power systemas
by: Tony Clark

For a specific power drawn from a battery system, lower voltages require higher current.
The main losses in battery systems are due to:
1. Battery internal resistance.
2. Cable resistance.

Cable resistance losses

As the current drawn on a 12V system to deliver (say) 480 Watts, a current of 40 amps would be needed. Any small resistance in the battery cables will cause significant loss of voltage.
eg a 0.01 ohm cable resistance will cause a voltage drop of 0.4 volts. This loss is approx. 3.33%

If a 24V system was used, due the lower current (20A) required to produce 480W from a 24v system, with the same cable resistance, the voltage drop would be 0.2V. In this case the loss is 0.0833%

For a 48V system, due the lower current (10A)required to produce 480W from a 48v system, with the same cable resistance, the voltage drop would be 0.1V. In this case the loss is 0.0208%

For all extra low voltage system, the battery and inverter low voltage cables should be as short as possible. Cables should be sized to minimise voltage drop at maximum load current, consistent with the system cost budget.

Solar panel output and battery charging voltages.

Where a solar charging regulator is used, the effective solar panel output is often about 2/3 of the rated output. This is because the solar panels are rated at a V mp of around 18v for a nominally 12V Panel. Thus when the panel is connected to the battery, the battery voltage is only raised slightly, while drawing the maximum current from the panel. Thus for a panel rated at 18V mp, 10A mp (180W), connected directly to a 12v battery, the panel can output a maximum of 140W (10A * 14V)

By using a Maximum Power Point Tracking charger, the panel voltage is maintained at the V mp for the panel and the Imp is drawn. The MPPT Charger converts the voltage from the V mp to the battery terminal voltage and the current fed to the battery is increased, delivering up to 95% of the rated panel power to the battery.
The panel delivers 18V, 10A (180W)
When the battery voltage is 12.0V, the charging current is close to 15A (close to 180W).
Another advantage of using an MPPT charger is that they are often rated for higher panel voltages, and may be suited for a range of battery voltages, often automatically configuring for the connected battery system.
Thus a string of 3, nominally 24V panels can be used to charge a 12V battery, with reduced losses in the solar panel cables.

Oct 11, 2012
12 or 24 volt
by: Glen Parkinson

Not sure when this question was posted but anyway I will give my comment just in case someone else has the same question down the track.

I would go at least 24 volt as a minimum, 48 volt is better. The higher voltage inverters tend to be more efficient with less losses. Plus your cable size not need to be as big as well as you can run longer cable runs.

The down side to the higher voltages is you need more batteries which is more costly however the higher the voltage the less amp draw on the batteries and the shallower the cycling.

I run 24 volts in my system and it works well. If I was to start all over again I would have gone 48 volts but 24 still does the job just fine.

Hope this helps.


Jul 15, 2010
Charging different battery banks
by: Anonymous

Thank you for your response on the 24 volt system. Is it easier to charge a 24v battery bank over charging a 12 volt battery bank. I am changing over my system from 12v to 24 v so I am trying to get all the possible information . Thank you

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