Linking solar panels together

#1
On top of my camper I have a single solar panel. I cannot identify how many watts or what mfg or anything. It does appear to work, although not great. I also have an Overland Solar folding 90 watt panel, that lives with the camper in it's case. Currently I hook up the folding panel when we are going to be stationary.
If I were to mount the folding panel permanently to the roof, what would be the best way to tie the two systems together? They both have their own controller and now I just attach each independently to the battery. Should this stay the same or is it better to splice them in together somehow.
I am all ears, as I don't know much about this stuff. Thanks for your advice.
 

java230

Adventurist
#2
It depends.

You really need to know the voltages of the two panels. (sticker is on the back usually!) If one is for example 12v and one is 24v, it will get necked down in the controller to the lower voltage.

Now if they are the same, there are two options, parallel or series. And this will depend on the controller. MPPT that can handle the higher voltage, go series.
 
#3
Connecting your panels in parallel I assume. I was talking with Renogy 3 yrs back about adding a 50 watt panel to my 100 watt & they mention solar panel with the lowest rated voltage determines the voltage output of the whole system. What they were saying my 100 watt would be cut down to 50 watt, l I'll have 100watts of power to my system. I went ahead & ordered a another 100 watt folding panel which gave me 200 watts.
 
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Code Red

Adventurist
#5
If you have an mppt controller, you might see better efficiency if you connect them in series. A PWM controller will pretty much be limited to nominal 12v (18-22 or so on the panel). An mppt works by playing with the overhead between the 14.4v or so your battery needs and what the panels are providing. So they will actually perform better if you give them more volts (within specs) to work with. You can also run thinner wires because you are using more volts and less amps to move the same watts.

I don't think the panels need to be the same size, so you might be able to connect them in series and see a benefit. i.e. you might be able to connect a 12v panel to a 24v. panel and feed 36v (or 48 or 96 or whatever) to the controller as long as you stay below the controller's maxv.

I bought a Victron mppt controller to replace the PWM controller that came with my Overland Solar panel. I got it more for the bluetooth monitoring than any performance gain, and honestly don't think there is much with only a single 12v panel. But it will take up to 100v @ 15 amps. I have been toying with the idea of getting another panel and running them in series. Internet wisdom (and we all know what that's worth) is that the mppt can get you another 30% or so from the same panels if it has enough overhead to work with. Not sure if its true, but its something for me to geek out over and tinker with while the beer goes down.

I don't really know what I'm talking about, but I did drive past a Holiday Inn last night.
 
#8
type of panel will make a difference also, I have & like the monocrystalline solar panels they tend to perform better than similarly rated polycrystalline solar panels at low or cloudy light conditions.
 
#9
The one thing they didn't test was having each panel on it's OWN controller, instead of trying to run both of them through one controller. Jscusmcvet indicated that each of his panels has their own controller, so perhaps he should just continue to run them that way.
 
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