# What happen if doing (3x24V panels in parallel) then series with 1x12V to make 36V?

Registered Users Posts: 8
Hi,
I have 1 12V 68W Unisolar flexible, and buying 3 24V 128W Unisolar flexible more.
I wonder if I can do:
- The 24V panels in parallel
- Then put them in series with the 12V panel
- Doing a 36V total to a MPPT charge controller, for a 12V battery bank.

I know the V will sum up, but what happens with the current?, because 3x24V in parallel will make ~9A, then that will flow in series thru the 1x12V panel which has ~3A...
- I guess the output current to the CC will be 3A finally?

Other way I can put all panels in series, making 84V and ~3A total, but I'm not sure of a MPPT charge controller under my budget wich can handle that to a 12V battery bank.

Background:
Why do I have this configuration?
I'm from South America, where solar equipment is very pricy, and mostly 12V appliances (that's why the 12V battery bank). I have been flying to USA twice a year, so each time I bought some thing. The only type of panel I can bring on the airplane are the Unisolar flexible.
I already have 1x68W 12V, a Xantrex C40, and a 12V Inverter.
I'm buying 3x128W 24V which are at a good price now, and a Rogue MPT-3024 for them.

But I wonder if I can connect all of them together to make them work under just one controller.

Sorry for the long message and explanation,
Thank you all.

• Banned Posts: 17,615 ✭✭✭
Re: What happen if doing (3x24V panels in parallel) then series with 1x12V to make 36V?

The information needed to give an accurate response to this would be the exact panel specs (Vmp, Imp). Particularly the current, because it will be limited by the lowest Imp rating in the string.

The three 24 Volt panels in parallel will have current 3X their individual rating. It is likely this will be far more than the one 68 Watt panel will handle.

Rough estimates: 128 Watts / 35 Vmp = 3.6 Imp and 68 Watts / 17.5 = 3.8 Imp
So the three in parallel become 10.8 Imp, and then the one smaller panel chokes it down to 3.8 Amps. Net results: 452 Watts of panel producing 199 Watts of power.

If you get two more of the 68 Watt panels you could make three strings of one 128 Watt and one 68 Watt each: 189 Watts per string, 52.5 Vmp 3.6 Imp
Three of those in parallel would give you 567 Watts. This would be over the Rogue's capacity on 12 Volts and would probably exceed its V max in.

Again, based on rough estimates of the panel specs not the exact numbers.
• Registered Users Posts: 8
Re: What happen if doing (3x24V panels in parallel) then series with 1x12V to make 36V?

both, 24v 128w and 12v 68W have
STC: Imp=4.1A
NOCT: Imp=3.4A

The reason for buying 128W instead of 68W is, currently they are almost at the same price, and due to my limited space on the airplane I cannot bring more than 2 (or 3 at most) panels.

I thought using the Rogue for the 3x128W, and the Xantrex C40 for the 1x68W which I can use also to expand in the future. Both CC in parallel to the 12V battery bank.

Your suggestion of strings of 128W(24V) + 68W(12V) is a good one. Currently I bought 2x128W(24V) and I already have 1x68W(12V) at home. I can buy 1 more 1x68W(12V) and make 2 strings. I'll loose 60W (128-68), compared to buying 1 of 128W.
I'll check if the Rogue can handle that Vmp.

Thanks
• Solar Expert Posts: 1,973 ✭✭✭
Re: What happen if doing (3x24V panels in parallel) then series with 1x12V to make 36V?
Galecra wrote: »
Hi,
I have 1 12V 68W Unisolar flexible, and buying 3 24V 128W Unisolar flexible more.
I wonder if I can do:
- The 24V panels in parallel
- Then put them in series with the 12V panel
- Doing a 36V total to a MPPT charge controller, for a 12V battery bank.

I know the V will sum up, but what happens with the current?, because 3x24V in parallel will make ~9A, then that will flow in series thru the 1x12V panel which has ~3A...
- I guess the output current to the CC will be 3A finally?

Yes, the 12V module will throttle down the current to 3A. You'll only get about 110 of your total nameplate 452 Watts from that arrangement.
• Solar Expert Posts: 5,183 ✭✭✭✭
Re: What happen if doing (3x24V panels in parallel) then series with 1x12V to make 36V?

You probably are better using a cheap PWM Cc on the small panel and a MPPT CC on the larger ones. Rogue MPPT?

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep