12, 24 or 48 Volts?

[tcrenshaw]

I have searched the board and I'm sure this has been hashed before but I can't find any postings. What are the pro's and con's of connecting my PV's in 12v, 24v or a 48v configuration? I was pretty much set on going with a 12v parallel setup because my panels are all 12v design. That would keep things simple. Yet I could easily go two panels series and then parallel those for 24v, just don't know which way would be best. I haven't purchased my charge controller yet.

[drdongle]

If your starting from scratch use 48V, smaller wire ( lower amps), longer transmission distance ( higher voltage).

Carpe Vigor

Dr.D

[Victor]

It mostly depends on the amount of power that you are going to be moving, storing , etc.

Personally I would go to 48 volts rather quickly, but this means buying solar panels in groups of four and 6 volt batteries in groups of 8. For a small demand this may be a bit overkill.

 Charge controllers are rated by amps so an MX60 for example will control 3000-3600 watts on a 48 volt system (60 amps X 50 to 60 volts) 1500-1800 watts on a 24 volt system and only 750-900 watts on a 12 volt system. This same economy applies to all of your current handling componants, wire, breakers, fuses, etc.

 48 volts will shock you, usually not much more than a stong tickle, under the wrong circumstances lethally.

 Long wire run in particular are much easier to swallow at 48 volts.

Make the wind fun!

Victor Creazzi

Aerofire Windpower

www.aerofirewind.com

[richhagen]

I would agree with the posts above for all but the most simple installations, where only one panel is used, or if you have specific use for power of a specific voltage like powering pre-existing 12 Volt devices, or 24V motors ect., I would use the highest voltage for which components are commonly available, which is 48V.  The reason is that the amount of power moved through a circuit is equal to the product of the voltage and the current.  The power lost in transmitting the energy over a wire is linearly related to the current only, and is independent of the voltage.

In other words,  Voltage Drop = Current multiplied by resistance, and Power = Voltage Drop Multiplied by Current.  The voltage drop and power lost is independent of what the starting voltage is so long as the starting voltage is sufficient that the output voltage would still be positive.  The resistance is generally a linear function of the area of the conductor for wires.  Also, for other components, such as diodes and rectifiers, the cost is usually much less for components rated for lower amperages.  

If you were to use a load or a diversion controller such as a Trace C-40 and move 30 amps through it, for the same cost of the device, you would be able to move 360 Watts through it at 12 Volts and 1440 Watts through it at 48 volts.  Hope this helps, Rich hagen

[richhagen]

One thing I forgot, at higher voltages such as 48 volt, it does become more important to have bypass diodes on your system as to limit the voltage drop across any one panel or portion if it were to become partially shaded.  In a higher voltage system, the voltage drop has the potential to be much higher and would thus be more likely to cause damage to the PN junctions on the cells.  Many new commercial panels come with that feature pre-installed, and if not, diodes can usually be added fairly easily.  Rich Hagen

[jacquesm]

Second that. But there is one pretty big 'But':

Higher voltage inverters are pretty pricey... (and usually they are also much better quality!).

[tcrenshaw]

Thank you all for excellent explainations. After taking all the info here into consideration and looking at cost of equipment I'm leaning towards a minimum of a 24v system. The 48v charge controllers and the need to put 4 of my panels together is kind of shying me away from 48v, but 24v looks to be the same cost.

[Trivo]

not sure about US or Canada but in Australia the MAX voltage that does NOT require a qualified electrician to do all the electrical work is 32v. if you use 48 v and there is a fire or someone gets killed you are in big trouble if you did the wiring

and no insurance

[BT Humble]

Home Power magazine (http://www.homepower.com) has had this discussion from time to time.  I'd agree with their conclusions, which were:

• For a Cabin or Trailer, use 12V (usually a small system, and equipment is cheaper);
  
• For a house use 24V or 48V (longer runs of cheaper wiring, less copper loss);
  
• For a grid-tied system (ie. feeding power back into the grid) use the highest voltage inverter available to you.
  
  

One interesting thing I've noticed is that 24V inverters are fairly common on e-bay, but fetch much lower prices than 12V inverters of equivalent wattage.  This is good news if you're buying! ;-)

BTH

[tcrenshaw]

The states are pretty easy. My father was Chief County Building Inspector for Napa and Yuba Counties for just about forever. My Uncle builds houses in Arkansas. In most states under federal code (UBC) you can do the work yourself and be your own contractor. You must pass inspection though to ensure that the work you do is safe and properly done. The use of a licensed contractor is supposed to protect the home owner and in many cases it does, sometimes not. And then it's different from state to state. Such as in California the inspections are very rigorous while in Arkansas there are few to no inspections at all for homes builders.

I think I'm going to go with 24vfrom the panels to the charge controller and 12v from the battery bank to the inverters which will be just on the other side of the wall in the battery shack. From there of course 120vAC into the house.

What has surprised me is that with three of my panels putting out about 40 watts each in full sunlight I'm still only getting about 70vAC out of my 220 watt inverter. This is no load output. So if it takes say six panels to run the inverter at full power, I'm thinking this little inverter is pulling some juice just to set their idle. Of course this is not with the battery bank in place. Now I'm understanding why there are remote shut off's for the larger inverters!

[ghurd]

""I think I'm going to go with 24vfrom the panels to the charge controller and 12v from the battery bank to the inverters which will be just on the other side of the wall in the battery shack. From there of course 120vAC into the house.""

Charging a 24v bank, and using them seperate at 12v is going to cause big problems.

The 70vac of a mod sine wave inverter could be the meter can't read it right.

Is it a 220w or a 220v?  Most of my cheaper meters show a 110v MSW inverter at around 90 to 100VAC, but it varies by the meter.

They all pull juice just sitting there, some a lot lot more than others. Some have a sleep mode, or load sensor that means if no load is present, the inverter is 'almost' off.

G-

[tcrenshaw]

I think you're mis-understanding. I'm going 24v from the panels to the charge controller. The charge controller will output 12v into the 12v battery bank. The drop from 24v to 12v is at the charge controller, not at the battery bank. Since the panels will be about 70 feet from the charge controller I want the higher voltage there right? Once I reach the charge controller which will be right next to the battery bank I won't need the higher voltage to help cover the distance because there really will only be a few feet between the charge controller and the batteries. The inverters will tap off there to, running 120v into the house. Or am I all mixed up on this?

I see what you're saying, the meter may have trouble with the interver because it's a modified sign wave intverter? The meter itself is fine, reads very well for normal AC house and DC batteries. No it's a 120v 220w unit. I've used it for several years now.

I'm sure my inverter doesn't have a sleep mode and it does seem to pull a lot of power while idle. It's pretty old so I expect it's not as efficent as modern units. I'll have to see what it'll do when I can actully provide it with 220w from the panels.

 

[ghurd]

Hold on! Couple problems here.

You will do a LOT better running 12v nominal to the controller using a larger wire.

Double the power actually.  Half the voltage, and therefore half the power will just be gone.  70' is not extreme.

Most 12v controllers will have a max Vin well below the 45-ish volts 24v of panels can reach.  25 or so volts will cook most of them.

Some people will say a max power point tracker controller will solve all your problems.  I say they read the brochure too many times.  Testing shows a gain of 4 to 8% usually.  Given the cost of those puppies, I say the same money is much better spent on more panels for a much bigger gain.  There could be some uncommon exceptions.

Most meters will not read MSW very well.  It gets them confused.

Old 220w inverter? Is it a big heavy Tripp-Lite?  They are not very efficient, but they seem almost bullet proof.  Very reliable.  Expensive.

How many watts and what kind of solar do you have?  I could give some more specific information if I knew about the panels.

G-

[pyrocasto]

If the charge controller converted the 24v to 12v(doubtful) it would double the amperage, but from the sounds of it that's not what he has.

Also, the gain of a traker depends solely on where you live. You can get almost 0 gain from them, or you can get over %100 more power. Also when you get one for free, like I did with my satilite dish, it's very nice power boost compared to the price of more panels.

[ghurd]

I think we are confusing trackers with trackers.  

I was talking about an electricial box (24v to 12v).  You are talking about a mechanicial box (moving the panels).

If he has 10 12v 1a panels. Connected in 12v, he has 10a.  Connected in 24v he has 5a.

A MPPT controller takes the 24v, converts it to 12v and doubles the amps to 10a.

Either way he only has 10 amps.

Why spend $350 for a MPPT to do what a $50 controller can do?  That frees up $300 for more panels, which will surely give him 4+ more amps.

The idea behind them is for times like when the PV can only make 10v, it will boost it to 13v so a little charging can happen.  Or like when the PV can supply 1a at 14v or 1a at 15v, it will convert the 15v to 14v at a little over 1a.

In most systems the gain is trivial.

I can sure see how the other tracker pointing the PVs toward the sun will increase output.  I think your design looks more reliable than the factory builts. Way Cooler.

G-

[pyrocasto]

Haha, my mistake.

What he said.