# 12 volt vs. 24 volt



## TxGypsy (Nov 23, 2006)

I had originally thought I would build my system with 12 volt panels, but I have had several people tell me to go with 24 volt panels. Of course several of these folks were trying to sell me 24 volt panels at the time  

Is there a reason to use one rather than the other? Are there complications or additional equipment necessary? Advantages or disadvantages?


----------



## 12vman (Feb 17, 2004)

The choice of voltage depends on how you want to use the power. If you are thinking of inverting to 120 v.a.c., then a higher voltage would make more sense. If you want to use smaller d.c. items, then 12 volts is a common voltage to work with. JMO..


----------



## Nimrod (Jun 8, 2010)

What system are you planning? Grid tied or off grid? A charge controller and batteries? 

If the voltage the panels puts out is higher then the wire from the panels to the charge controller can be a smaller size (bigger guage number) so it costs less. There are charge controllers that take a higher voltage from the panels and converts it to 12 volt for chargeing the battery bank. 

You can wire 12 volt panels so the whole array puts out higher voltages too.


----------



## wy_white_wolf (Oct 14, 2004)

My basic rules
12 volts is for toys and RV&#8217;s
Panel wattages 300 watts to 1000 watts use 24 volt battery
Panel wattages higher than 1000 up to 4000 use 48 volt
Higher voltages allow for the use of smaller wiring and have less voltage line loss.

Charge controller can handle higher wattages at higher voltages. So you need less of them on a larger system.

If you're going to use a MPPT charge controller then I would look at panels intended for grid tied applications. Because most systems built are for grid tied they are cheaper. They can be wired in series for higher voltages and most quality MPPT charge controllers will accept up to 150VDC from the array.

WWW


----------



## Studhauler (Jul 30, 2011)

If a guy is not going to grid-tie, and run household lights and other necessities on a 12 vdc system, and have an inverter for 115 vac system for power tools and such; would you still recommend the 48 volt system? 

Someday I plan on using one or two small windmills and a small solar panel array.


----------



## Gray Wolf (Jan 25, 2013)

24 volts DC is about as high as you can go and find household things to run directly, like ceiling fans. 24 volts is what our off-grid system is: 8 panels at 235 watts and 16 batteries at 6 volts each. It powers our efficient 3,400' house by inverter and is set up to run 7 DC ceiling fans at 24 volts each. Fat city when the sun shines. Generator city after a couple of stormy days.

If you don't care about running things, 48 or higher in your system would be better from an efficiency standpoint. It might be hard to find high wattage 12 volt pannels these days and with a MPPT controller the pannel voltage doesn't matter much anyway. I'd look at 24 volt pannels (they aren't really 24 volts but that's the way to think of them) and you can wire them to be 24, 48.... to match your inverter and charge controller.

I stopped at 24 volts for another reason though - fear of high voltage/amperage DC in a large battery bank like us people living off-grid always have. Accidents happen and I think you are pretty dead holding on to anything more than 24 DC, and need a bit of luck even with 24 volts. I'd like to hear more on this from somebody who actually knows though. I could be wrong about the whole thing and should have gone 48. 

In any case, DC doesn't "let go" of things and people like AC does. That is why you should use DC rated switches, breakers, etc.

Fear also drove me to heavily plastic dip all but the head of hand tools used near the system so a wrench dropped across the wrong spot won't arc.

Yes, I'm conservative to say the least.

Don


----------



## 12vman (Feb 17, 2004)

Quote.. WWW..

My basic rules 

12 volts is for toys and RV&#8217;s
Panel wattages 300 watts to 1000 watts use 24 volt battery
Panel wattages higher than 1000 up to 4000 use 48 volt
I'll disagree with #1.. 

I built my metal roof, my rabbit hutches, my chicken coop, cut all of my lumber remodeling, ect, ect. using 12 volts and a 400 watt inverter to charge my cordless hand tools. 

I plan to grow my system this summer to 900 watts, using an Outback MPPT charge controller with series connected 12 volt panels @ 48 volts input. My working house voltage will remain at 12 volts because I have 20+ yrs. of development designed around 12 volts..


----------



## Studhauler (Jul 30, 2011)

I am staying away from cordless tools except one cordless drill because it is so handy. Cordless tools, specifically the battery only last about 5 years, then it is about the same price to buy a whole new tool than to replace 2 or 3 batteries. Corded tools last a life time or two. :hijacked:


----------



## Studhauler (Jul 30, 2011)

Thanks 12vman and WWW for the info so far. On a 48 volt battery bank system, is it possible / practical to take 12 vdc from the battery bank to use for lights and fans? Then at the same time use the 48 vdc battery bank to run an inverter?


----------



## 12vman (Feb 17, 2004)

_"On a 48 volt battery bank system, is it possible / practical to take 12 vdc from the battery bank to use for lights and fans? Then at the same time use the 48 vdc battery bank to run an inverter?"_


Sure 'nuff..  Example..

http://www.newmartelecom.com/DC-DC-Converters-Rackmount/Rackmount-DC-Converters.html

You would need to have some idea of how much 12 volt load that you would ever need/expect and match a units output limits to fit your loads. I have one 30 amp fuse in my main power buss that carries everything that I normally use. (Lights, TV's, Pumps, Radios, Stereos, Ect..) I never popped that fuse. My 2000 watt inverter is on a seperate circuit direct to the battery and is fused accordingly..


----------



## Jim-mi (May 15, 2002)

That link 12man put in is too the 'upper end' kind of Tell-Com equipment. 
Excellent----but----pricy.
There is a big bunch of more moderately priced converters for 24 to 12 volt.....

For years I have been using a Vanner Voltmaster 100amp 24 to 12 converter . . .really good stuff. . . .tho pricy....

I have heard some peoples tap the battery bank at 12 volts and run loads like a 1000watt coffee pot...................

This is a very bad practice and will lead to a much shortened battery life.........


----------



## jwal10 (Jun 5, 2010)

TxMex said:


> I had originally thought I would build my system with 12 volt panels, but I have had several people tell me to go with 24 volt panels. Of course several of these folks were trying to sell me 24 volt panels at the time
> 
> Is there a reason to use one rather than the other? Are there complications or additional equipment necessary? Advantages or disadvantages?


 
Makes a big differece what you want in the end. Large power uses or small direct 12 volt uses. 24/48 volt can use smaller wire, give longer runs. More equipment=more cost. I am all 12 volt. I charge my cordless tools through a 12 volt vehicle type charger here but I have a 110 charger if it is available....James


----------



## TxGypsy (Nov 23, 2006)

I should have explained more about my specific needs. Sorry about that. I've been researching 'whole' system set ups....folks describing what they have and what they use it for. I've come to the conclusion that I need far less power than I had originally thought when I was looking at solar power dealers sites.

At first I am going to run a very efficient refrigerator and a couple of dc lights in an RV(fema trailer, so not built in dc) while I build a very small cabin. Probably 800 ft or less. Once I have the cabin built I plan to use as many dc devices as possible. My lights will be LED's. I'll be running a couple of 02 cool fans. A couple of small dc water pumps. A laptop, and I'll need to recharge cell phone and kindle from time to time. The major draw will be my vitamix blender which will be one of the few AC items in the house. I'll also have a dc swamp cooler(on 12v it uses 73 watts). For power tool use I plan on running the generator. So not a whole lot of stuff compared to most folks. 

I love to travel and it would be awesome if I had a system that would travel with me.


----------



## Gray Wolf (Jan 25, 2013)

Somewhere - there is a break point where the cost of 12 volt appliances and lighting is greater than the cost of doing the whole thing at 120 AC - run smaller wire, you can use standard AC outlets and switches, buy lightbulbs and household appliances at the corner store etc. And perhaps easier resale and/or financing with a 120 house.

You're going to have an inverter anyway and the power loss of a GOOD inverter can be pretty small. I'd give some thought to going 120 AC.

We live off-grid on solar in a 3,400 sf "normal" house and only use 24 volt DC for 7 ceiling fans. (They cost more to buy than AC but DC motors are pretty efficient) We have a LOT of switched circuits to really use zone lighting and to kill phantom loads to microwave etc. For instance, our bedroom/bath has 7 light switches and our kitchen/living room has 8. And we are very aware of what's switched on! Recharge cordless stuff only during sunny days etc etc. Off-grid works!


----------

