# What is the difference between a 12V, 24V, 48V solar System?

hmong2017
Registered Users Posts:

**35**✭✭
For an off grid Solar panels, breakers, controller, batteries and inverter.... Whats the REAL difference to choose from a 12V, 24V and 48V system? Why do others choose a specific system vs others?

I only see that they all produce electricity and makes 110 and 120volts....

Is bigger ones like 24v and 48V just simply charge batteries faster or what?

I only see that they all produce electricity and makes 110 and 120volts....

Is bigger ones like 24v and 48V just simply charge batteries faster or what?

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## Comments

4,451✭✭✭✭✭A 12v system would also require 4x the charge controller capacity. Eg. 1200w would be 100a out from12v controller, likely needing 2 units. 25a out from a 48v controller easily handled by one. A 60a controller handles ~ 60x12v=720w of panel, same 60a controller is ~ 60x48v=2880w on a 48v system.

So, for larger systems, higher nominal voltage makes more sense. Offsetting this is, for smaller loads and systems, lower system voltage tends to be more efficient and cost effective.

There is no best choice, it depends on loads.

Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

30,037adminFor example, we say that roughly 100-150 Amps for the battery bank current, then for a 12 volt bank, I would suggest the largest AC inverter or DC loads would be roughly (ignoring losses and variable battery bank voltage) in the range of:

- 100 amps * 12 volts = 1,200 Watts maximum suggested
- 150 amps * 12 volts = 1,800 Watts not to exceed if avoidable

For 24 and 48 volt banks:- 100 amps * 24 volts = 2,400 Watts max suggested
- 150 amps * 24 volts = 3,600 Watts not to exceed...
- 100 amps * 48 volts = 4,800 Watts
- 150 amps * 48 volts = 7,200 Watts not to exceed

In reality, if you heavier (and paralleled) copper DC cabling, you will find 12, 24, 48 volt inverters that are larger than the above recommendations, and they can work... But exceed the max suggested is better done with higher voltage battery buses (24 and 48 volts).Sending 100's of Amps at 12 volts--Really only leaves you about 0.5-1.0 volts of drop on the DC battery bus for a "workable" system... For 24 volts, 1-2 volts, and 48 volt 2-4 volts drop--So you have more "headroom" with the higher bus voltages (and allows a larger DC load if needed and properly designed).

Similar issues for charging your battery bank... For example a good quality MPPT controller can output 80 amps... At 12/24/48 volts. So, a higher voltage battery bank means a larger solar array could be supported... For example, our rules of thumb would suggest the maximum array for an 80 amp charge controller:

- 80 amps * 14.5 volts charging / 0.77 panel+controller deratings = 1,506 Watt maximum "cost effective" array
- 80 amps * 29.0 volts charging / 0.77 panel+controller deratings = 3,013 Watt maximum "cost effective" array
- 80 amps * 58.0 volts charging / 0.77 panel+controller deratings = 6,026 Watt maximum "cost effective" array

The same $600 controller can support much larger arrays with higher battery bus voltages.Anyway, details matter here. The above are good rules of thumbs to estimate a workable system without going into a bunch of detailed design issues. But they can be modified as needed.

-Bill

5,101✭✭✭✭If you are looking for inverter sizing, you will find that inverters that are UL1741 (for home use) rarely are far from the sizes Bill has mentioned above. Magnum makes a 2800 now 3000 watt inverter for mobile use and it only carries UL458 (mobile use) They do make the MS2000 12 volt which I think is rated for 2000 watts continuous. They also make a 4000 watt 24 volt, largest I'm aware of in 24 volt. I believe there are a couple 8000 watt 48 volt inverters, Outback's Radian, and Schneider? larger than that and you would have to 'stack' inverters. So just to be 'legal' you may find these ranges.

1✭30,037adminI would suggest that you start a new discussion (thread) about your system needs.

Off grid solar power is pretty expensive--Something like 5-10x the cost of utility power. So you want to 1) make sure your power needs are reduced to the minimum amount you need through conservation/new energy efficient devices, etc. And 2) you need to measure your loads (average Watts, Watts*Hours per day of usage, etc.) so you can size the system to support your needs.

The voltage and Amp*Hour rating of your battery bank are based on the amount of energy you need per day. Fork lift batteries are among the longest life batteries (10-15+ years), but there are not cheap, and they are very large/heavy to move (1,000-2,000 lbs or so typically). Plus they need a larger solar array (+~30% larger) and need more maintenance (checking electrolyte levels and adding more distilled water) than other lead acid batteries (they tend to be "less efficient" and use more distilled water than other FLA (flooded cell lead acid) Batteries.

Any way, start a new discussion about your system needs and tell us more about your energy needs, and we will go from there.

-Bill

298✭✭✭2,903✭✭✭✭12 volts - under 800 watts.

24 volts - between 800 and 1600

48 volts - living full time off grid with full complement of amenities - over 1600 watts of panels. The wiring is twice as efficient when voltage is doubled as has been pointed out. Better battery layouts are easier to achieve (says the guy experimenting with four strings - and loving it so far).

79✭✭475✭✭✭30,037adminAlso, tends to be easier to find smaller wattage AC inverters at low voltage... 48 Volt inverters tend to be larger anyway. Although, in the last few years, the lower power 48 volt input inverters are at least available now.

Our host has a 48 VDC inverter down to 250 Watts:

https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_input_voltage=439

https://www.solar-electric.com/victron-phoenix-48-250-120v-nema-5-15r-inverter.html

- Output AC voltage: 120VAC +-3%
- Output frequency: 60Hz
- Continuous output power at 25oC: 250VAC
- Peak power output: 400W
- Max efficiency: 88%
- Output Socket: NEMA 5-15R
- Dimensions(h x w x d): 3.4" x 6.5" x 10.2"
- Weight: 5.3 lbs
- Warranty:5 years

The 12 volt version of the same above inverter is only 4.2 WattsZero load power: 7.9 Wattshttps://www.solar-electric.com/lib/wind-sun/Phoenix-Inverter-VE.Direct-250VA-1200VA-DS.pdf

Not a huge difference... And for larger systems (which 48 volt systems tend to be), not going to make much of a difference.

-Bill