diy solar

diy solar

Paralleling solar panels

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SubnetMask

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This is going to be a dumb noob questions... I've been running a Harbor Freight 100w solar panel for a small experiment setup and just grabbed a second one with the intent being to parallel them (They say not to use in series - any ideas why?), but they don't say anything about parallel. When the sun was shining good and bright, one panel was putting about 90w through the renogy MPPT controller, and it seems both panels are putting out pretty much the same wattage for a given light level when alone, but when the single panel was putting out 90w and I connected the second panel, the wattage only went up by about 50% - with both panels putting out 90w, I would have expected it to go up to around 180w. So is there something special that should be done when Paralleling solar panels, or are my expectations incorrect?
 
Post the full specs of the panels and the solar charge controller (SCC). Tell us what gauge and length of wire is running from the panels to the SCC.

Also note that if the battery nearly full and there are no loads then you won't get much out of the panels because there's no use for the power.
 
The panels are these from Harbor Freight. Can't really give any more specs on the panels other than 100w 18-19VDC because the info doesn't seem to be there. The controller is a Renogy RNG-CTRL-RVR40-US, wiring is all 10Ga, from the panels to the controller is 10', maybe a tad longer and from the controller to the batteries is maybe 4' (battery is not in the same box as the controller). Using MC4 connectors, not the connector that came on the solar panel.

The main battery I've been using is a Duracell 35Ah sealed/AGM deep cycle, and the thought if the battery not needing the energy had crossed my mind as it was only showing about 30w when I first started with adding the second panel, so to test that theory, I shut it down, disconnected that battery and connected four paralleled 18Ah batteries that were in the 50-60% SOC range to test the theory and that's where I was able to get more wattage flowing, but still not what I expected with the two panels.
 
SubnetMask said:
The panels are these from Harbor Freight. Can't really give any more specs on the panels other than 100w 18-19VDC because the info doesn't seem to be there. The controller is a Renogy RNG-CTRL-RVR40-US, wiring is all 10Ga, from the panels to the controller is 10', maybe a tad longer and from the controller to the batteries is maybe 4' (battery is not in the same box as the controller). Using MC4 connectors, not the connector that came on the solar panel.

The main battery I've been using is a Duracell 35Ah sealed/AGM deep cycle, and the thought if the battery not needing the energy had crossed my mind as it was only showing about 30w when I first started with adding the second panel, so to test that theory, I shut it down, disconnected that battery and connected four paralleled 18Ah batteries that were in the 50-60% SOC range to test the theory and that's where I was able to get more wattage flowing, but still not what I expected with the two panels.
Click to expand...
Not only will the SCC not put power into a full battery, but batteries can only suck up so much power at a time. Even 4 18Ah batteries can't suck up much due to the lack of plate mass. I think if you were wanting to really try to load test those panels, grab your big battery, an inverter, and something like a heat gun and really put some load on the battery. You should see the panels really ramp up then if they've got good light.

Still, getting 90w out of a panel, especially a HF panel, is pretty impressive!

FWIW, the only specs it gives in the manual are Rated Output 18 VDC / 100 W / 5.56A which I'm guessing means 18VoC and 5.56Imp. That's odd considering the product page says DC Volts24???
 
Also, after doing some digging, you're not the first person to have this issue:

These are pretty good panels, finally. Glad to see they are getting away from the the plastic frame temporary stuff and offering something with a more serious build quality to it. I've purchased seven (7) of these and really like them. Their portability is excellent. I get a maximum of 96W out of each panel. I tried them in parallel but the numbers don't combine to get full power. They actually increase in a decaying order. So I connect them in series (4 on a string) and get great numbers that way. But had to use some 10 awg wire for combining them and extending to my charge controller. The SAE connectors are ok, but they need to be replaced with the water proof MC4 type. I haven't done this upgrade yet but it's pretty easy with the right tools. The mounting hole on the backs of these work well with the Z-bracket kits you can get from Amazon. Oh, and it looks like they sell really well. Usually have trouble finding them in stock. And the price just went up from $109 to $119. So there's that.
Click to expand...

Maybe rewire in series and give the MPPT controller a shot at them?

I'm glad I found out about this now before I re-did the 12v system on my brothers pop-up. I was planning on 2 of those in parallel so I could face them different directions. :(
 
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Well, the label on these panels say not to connect in series.... They have a box on the back that looks like it should contain a bypass diode, so I don't know... Any ideas why?

So I'm guessing there's nothing special that needs to be done to parallel the panels like diodes or something, and my results are just typical of just not being able to suck up enough power?

And in reality, in really good light, the SCC has reported as high as about 132W from a single panel! It only seems to do that when the light is really bright in a really clear sky and when the air temp is COLD. The cold temp probably helps them wring out a little more.
 
That post you quoted - I'm assuming the poster was referring to HF panels? TBH, I didn't read the quote at first, I read your reply, but when I re-read it, apparently the poster has hooked them up in series. Could the reason they say not to hook up in series be because they expect/intend that they'll be used with their 'charge controller' that's not meant to handle the 44 or so volts two panels (or more) could be capable of creating? Just wouldn't want to hook them in series and then damage them.
 
Yeah, that was a posted review for those panel. I'm guessing the same thing that plugging 40+v into their little SCC would be a "Bad Thing".
 
Well, I grabbed a fairly cheap inverter and gave it a test with the panels in parallel and in series and I'd say the results were pretty good. The only issue was when I stood in front of one of the panels to see if they could continue generating power with one of the panels covered, current dropped to zero. If I'm not mistaken, the diode in the box on the panel is supposed to allow other panels in a series array to continue to supply power if one or more are covered for whatever reason. If that's correct, then it would seem these don't have a diode.

Screenshot_20220214-113843_small.pngScreenshot_20220214-114332_small.png
 
SubnetMask said:
If that's correct, then it would seem these don't have a diode.
Click to expand...
With 12v panels any bridging diodes, within the panel, would be redundant because if they were needed the voltage across bridged rows would be less than what the system voltage requires.... 4 rows of cells with diodes across each set of 2 rows is half Voc =10v,
In series, bypass the whole panel with a diode. In parallel skip the diodes, bypass & blocking.

Panels have max output at a certain voltage and it doesn't effect maximum power output if they are in parallel or series if V is the same across all panels in both arrays. In series the higher voltage allows the MPP CC to react over a wider range.
 
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sunshine said:
With 12v panels any bridging diodes, within the panel, would be redundant because if they were needed the voltage across bridged rows would be less than what the system voltage requires.... 4 rows of cells with diodes across each set of 2 rows is half Voc =10v,
In series, bypass the whole panel with a diode. In parallel skip the diodes, bypass & blocking.

Panels have max output at a certain voltage and it doesn't effect maximum power output if they are in parallel or series if V is the same across all panels in both arrays. In series the higher voltage allows the MPP CC to react over a wider range.
Click to expand...
I found this post regarding bypassing panels - I'm guessing this is the kind of setup I'd want if I want to be able to bypass a panel if it's shaded? What would the best way to accomplish wiring this up be?
 
Most solar panels have 2 bypass diodes. I'm sure the super cheap (not inexpensive) ones from Harbor Freight are an exception. They don't even provide full specs for their panels. The 100W panels from Renogy (not that I'm recommending Renogy) have bypass diodes.
 
Here's the box on the back of the panels - looks like it should have diodes in it... in theory...
solar bypass.jpg
 
SubnetMask said:
The only issue was when I stood in front of one of the panels to see if they could continue generating power with one of the panels covered, current dropped to zero.
Click to expand...
Was that in series and you shaded the string or parallel and the other should have picked up the slack? Normally when you shade part of a string, the whole string gets nerfed hard. That's the big advantage to parallel is shading one panel shouldn't affect the output of the other panel.
 
SubnetMask said:
I found this post regarding bypassing panels
Click to expand...
You can see the ribbon connecting the rows of cells from the front of the panel or hold it up to the sun to view from the back to see how it works.
Maybe they use the same panel with 2 diodes in the junction box that they sell as being suitable for a series array that they just leave out for your model. Open the box and see.

Edit. By opening the box you should then see the best way to bypass the panel by soldering a diode across the out terminals.
 
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Rednecktek said:
Was that in series and you shaded the string or parallel and the other should have picked up the slack? Normally when you shade part of a string, the whole string gets nerfed hard. That's the big advantage to parallel is shading one panel shouldn't affect the output of the other panel.
Click to expand...
Yes, that was in series. As a noob, based on bits I've read, I thought that in a series string, if one was shaded or not producing for whatever reason, the diodes would allow current from the other panel(s) to bypass the shaded panel and continue to power the controller/load. But of course, I may be missing something.
 
SubnetMask said:
Yes, that was in series. As a noob, based on bits I've read, I thought that in a series string, if one was shaded or not producing for whatever reason, the diodes would allow current from the other panel(s) to bypass the shaded panel and continue to power the controller/load. But of course, I may be missing something.
Click to expand...
Assuming your panels have bypass diodes (a junction box on the back of the panel doesn't necessarily mean there are bypass diodes) then what you state is how I understand it.
 
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