Combining Somewhat Dissimilar [12v] Panels in Parallel

carbon60

Explorer
Hi All,

I'm not quite clear on this piece, so I'd like to get your collective input.

I have a pair of 100W Renogy "suitcase" panels that I run in parallel or separately depending on my requirements and the vehicle combination I'm using. The specifications for these units are as follows:

100W Renogy Eclipse "Suitcase" PanelRNG-KIT-STCS100MB-NC-BC
Vmp17.6V
Voc21.6V

This setup works really, really well. Next, I would like to add a fixed panel to the roof of my trailer and possibly to my truck as well. I can fit a 160W panel in those locations and, well, more is always better, right? But the 160W Renogy panels have slightly different specs:

160W Renogy FlexibleRNG-160DB-H-BC
Vmp19.1V
Voc23.0V
160W Renogy RigidRNG-160D-SS-BC
Vmp20.2V
Voc22.9V
100W Renogy FlexibleRNG-100DB-H-BC
Vmp18.9V
Voc22.5V
100W Renogy "Eclipse" RigidRNG-100MB-BC
Vmp17.7V
Voc21.2V

My question is can I wire one, or more, of these permanent panels in parallel with one, or two, of the existing portable panels despite the small voltage differences?

Thanks for your help,

A.
 
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rayra

Expedition Leader
I wouldn't think the controller would care. All it 'sees' is voltage / amps at the input. Doesn't care what the source(s) are, as long as they're within the acceptable range. If the controller has somewhere to put it, power flows.

/but I'm not a 'Solar Expert', despite having stayed in a Holiday Inn Express recently
 

dreadlocks

Well-known member
if your running both fixed and portable, it'd be better to run two seperate controllers.. then its moot.

since both will be in different locations, both cant be expected to have the same lighting conditions.. with blocking diodes this means the partially shaded panel on your roof wont be doing much of anything whereas it could be scavenging at least something if it was on its own controller.
 

carbon60

Explorer
if your running both fixed and portable, it'd be better to run two seperate controllers.. then its moot.

since both will be in different locations, both cant be expected to have the same lighting conditions.. with blocking diodes this means the partially shaded panel on your roof wont be doing much of anything whereas it could be scavenging at least something if it was on its own controller.

Very good points. So maybe I run EITHER the roof panel OR the portables, depending on conditions.

Thanks for your reply.

How close do they need to be, in reality, to run in parallel?
 

dwh

Tail-End Charlie
If your controller is PWM a small diff in Vmp doesn't matter since the solar will be operating at battery voltage instead of Vmp anyway.

If MPPT it's gonna find a voltage value to get max watts, which will end up being an average. So say it chooses 18v - the 17v panels will be running a volt over their Vmp and the 19v panel a volt under.

A small loss in overall efficiency, but not really any worse than you'd accept by flat-mounting a panel in the first place. In other words, not enough to worry about.

If you're gonna do it, just try to keep the Vmp diff to a minimum.
 
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dwh

Tail-End Charlie
The question is...are the controllers on the suitcases going to be able to handle the extra watts?

Dunno. But for a permanently mounted fixed panel, I'd want a permanently mounted controller as, well.

So yea, you'd probably be better off getting a controller for the fixed panel on the trailer so it can work full time when there is sun. Same if you put one on the truck as well. Then just add the suitcases with their controllers on an ad-hoc basis when needed.
 

luthj

Engineer In Residence
Plus minus 10% in vmp is fine, but don't forget about shading effects on a single panel pulling the other down.
 

carbon60

Explorer
If your controller is PWM a small diff in Vmp doesn't matter since the solar will be operating at battery voltage instead of Vmp anyway.

I only use PWM controllers, so that's perfect advice. And I didn't really understand that point, so thank you for the explanation.

A small loss in overall efficiency, but not really any worse than you'd accept by flat-mounting a panel in the first place. In other words, not enough to worry about.

If you're gonna do it, just try to keep the Vmp diff to a minimum.

The above makes sense to me.

The question is...are the controllers on the suitcases going to be able to handle the extra watts?

My suitcase units have no controller, I only use controllers permanently installed in my vehicles. I don't understand why one would want the controller at the wrong end of a long cable, or at a greatly differing temperature than the battery bank.

Plus minus 10% in vmp is fine, but don't forget about shading effects on a single panel pulling the other down.

These panels all have "blocking diodes", does that completely prevent shading issues or just help a bit?

I think I might set up a "1,2,1+2" switch, just so I can study the output under differing conditions and school myself.

Thanks all,

A.
 

luthj

Engineer In Residence
These panels all have "blocking diodes", does that completely prevent shading issues or just help a bit?

To many variables to know for sure. Blocking diodes help a lot, but partial shading can pull a panels voltage down enough to affect he other panel depending on diode configuration. Its generally a a big deal, but something to keep in mind if every watt counts.
 

Photobug

Well-known member
I am considering doing the same. A small panel on my trucks roof to charge while driving. Then when camped out I would plug in a portable 100+ watt panel.
 

dwh

Tail-End Charlie
My suitcase units have no controller, I only use controllers permanently installed in my vehicles. I don't understand why one would want the controller at the wrong end of a long cable, or at a greatly differing temperature than the battery bank.

"The wrong end" is a common misconception. A circuit is a circle - there are no ends.

For PWM, which is just a high-speed chatterswitch, it doesn't matter where in the circuit the switch is.

For MPPT it matters, since there are two circuits operating at different voltages, one for the solar and one for the battery. In that case, having the controller closer to the battery to minimize loss due to resistance on the battery side is worth doing since the battery side operates at a lower voltage / higher amperage than the solar side.

The point about temp is a valid point, though I would question just how "great" the temp diff really is.


These panels all have "blocking diodes", does that completely prevent shading issues or just help a bit?

I describe the effects of bypass diodes and shading here...

https://www.expeditionportal.com/forum/threads/roof-solar-panels-go-2-50w-or-100w.176160/

Honestly, I'm a bit confused by this talk of "blocking diodes" and a shaded panel "pulling down" another panel. Not sure exacly what is meant by that...
 

Rando

Explorer
With both PWM and MPPT charge controllers, you want the charge controller close to the battery. The charge controller needs to sense the battery voltage in order to know when to switch between bulk/absorb/float and it senses this voltage over the same wires that the charge current is flowing on. If there is a lot of wire between the controller and the battery, the voltage drop in that wire will cause the charge controller to switch out of bulk too early and not fully charge the battery.
 
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dreadlocks

Well-known member
I am considering doing the same. A small panel on my trucks roof to charge while driving. Then when camped out I would plug in a portable 100+ watt panel.

For a truck a roof mounted panel wont provide any use driving, yer alternator will have more than enough charging capabilities.. now when you park and shut off, thats when it'll be doing its job.. for a trailer its another story, my fixed roof top panel does charge while driving, because the trailer wiring can only provide a few amps.. it was either fixed solar, or run heavy gauge charging circuit independently from the trailer plug.

Fixed panels need no setup or thought, you can park at a trailhead and go for day long hike and not worry about coming back to a flat battery or missing portable panel AND a flat battery.. you end up only deploying the portable panels when you need it, like you parked under a big tree and dont get much direct sunlight at all or the rooftop is not enough on its own.

The sweet spot for lead banks is ~200W per 100AH, unless you've got more than that.. it should not be an EITHER/OR situation.. use em BOTH.. or you are gonna be leaving free energy on the table.
 
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Photobug

Well-known member
For a truck a roof mounted panel wont provide any use driving, yer alternator will have more than enough charging capabilities..

My house battery is in the back of my truck and is not connected to the alternator. My impression is to get any adequate charge from the alternator I would need a DC-DC charger and some very heavy cable connecting the two. That is more work than i want to put into getting an alternator charge going for now as I am concentrating on solar. Since you talked me out of getting a fridge my solar needs will likely be minimal for now.
 

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