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Old 21-08-2019, 13:07   #1
TCL
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New Solar Installation - Odd Results?

I'm hoping for some constructive thoughts on diagnosing what seems to be odd results on my first solar panel installation.

I finally got my solar panels mounted and wired in, along with the solar controller, monitor, etc., Monday evening. Granted, yesterday was overcast all day and itís only been low-angle morning sun this morning, but Iím seeing what appears to be an odd result. Note: I'm not focused (at this point) on the total volts/current produced but the amounts relative to one another. Namely, if my understanding is correct, the outputs read as if theyíre wired in series, but Iím almost 100% certain theyíre correctly wired in parallel (as I intended).

My understanding is:
Multiple panels wired in series = voltages additive, amps stay the same
Multiple panels wired in parallel = voltages stay the same, amps additive
In other words, two 170W-rated panels at 12V:
Series Ė 24V, 14 amps
Parallel Ė 12V, 28.33 amps

To wire in series, positive terminal of one panel to negative terminal of second panel
To wire in parallel, connect the two positive terminals together and the two negative terminals together

I intended to wire in parallel. For each panel, I connected the 12AWG panel wire from the positive terminal to a 12AWG red wire using an MC4 connector; and the 12AWG panel wire from the negative terminal to a 12AWG black wire using an MC4 connector, then used ring terminals on the opposite ends of each of the red/black wires to connect to a junction box. At the junction box, I connected 10AWG red (positive) and yellow (negative) wires from the junction box to the solar controller.
Iíve attached photos.

The positive and negative terminals on the panels are clearly marked (hard to see from photo without zooming, but Iíve annotated); they correspond to male and female MC4 connectors, respectively.
Itís hard to see from the photo, but I just quadruple-checked that the positive wires are connected to my red wires.
The photo of the junction box shows that all the red(+) are connected to one post and all the black/yellow (-) are connected to the second post.
So I believe that this is the correct way to wire in parallel.

But the photo of the results from the Victron Connect app shows 27.03V, 6.3A Ė which for two 12V panels, seems like itís adding voltage, not amps.

Any thoughts to help make sense of this would be greatly appreciated.

Additional details:
- (2) SunPower SPR-E-Flex-170 170W semi-flexible panels
- Victron SmartSolar MPPT 100/30 controller
- Victron MPPT control
- (6) 6v / 225 Ah lead cell batteries, wired in series/parallel, i.e., 12v / 225 Ah * 3 = 12v / 675 Ah battery bank
Attached Thumbnails
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Old 21-08-2019, 13:25   #2
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Re: New Solar Installation - Odd Results?

It depends on the voltage rating of the panels. There should be an open circuit voltage on the panels. The low angle of the photo makes it difficult to count the cells but it looks as though they might be 48 cell panels which are nominally 24 volt panels, but you have an MPPT controller so all is well. Given the conditions you describe getting 50% of their rated power is quite good.
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Old 21-08-2019, 14:11   #3
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Re: New Solar Installation - Odd Results?

Agree. If you have two 24-28 volt panels, that's exactly what you want to see. The Victron display upper half info is the panels (parallel combined in your case) and the lower half is what it's doing for charging the 12v nominal house bank.

Edit: https://us.sunpower.com/sites/defaul...-170w-4x12.pdf Shows them as 29.9v panels.

Did you do any voltage drop calculations with your 12 awg? You may get more power from a larger wire.
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Old 21-08-2019, 14:55   #4
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Re: New Solar Installation - Odd Results?

A quick googling tells me what the plate on the panels should have told you


Model SPR-E-Flex-170
Nominal Power(Pnom) 170
W Power Tolerance +/–3%
Rated Voltage (Vmpp) 29.9 V
Rated Current (Impp) 5.79 A
Open-circuit voltage (Voc) 34.8 V
Short-curcuit current (Isc) 6.10 A
Power Temp Coeffiecient –0.30%/į C
Voltage Temp Coefficient –83.7 mV/į C
Current Temp Coefficient 3.5 mA/į C
Max.System Voltage 45 V
Series Fuse Rating 15 A


So they are nominal 24V panels and you do have them wired in parallel.


And as Captain Bill says, that output is good for the conditions you describe.
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Old 21-08-2019, 19:16   #5
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Re: New Solar Installation - Odd Results?

Thanks, all. I obviously misunderstood what I was supposed to be seeing. Much obliged.
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Old 22-08-2019, 08:58   #6
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Re: New Solar Installation - Odd Results?

Just one comment on the installation. I first did mine the same as yours with white zip ties. They died in the sun almost as fast as I installed them. A little longer if they were shaded by the panel. Black ones last better but the best I have found are stainless steel. They last like you would expect them to. Check Amazon for them and also you tube for installation video.
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Old 22-08-2019, 16:18   #7
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Re: New Solar Installation - Odd Results?

+1 on the stainless ties-- Harbor freight has them as well just be careful because they can have some sharp edges . good luck with your new setup
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Old 22-08-2019, 16:32   #8
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Re: New Solar Installation - Odd Results?

Quote:
Originally Posted by TCL View Post
I finally got my solar panels mounted and wired in...
It could be an optical illusion, but those panels look like they will pool water they way they are installed. At the very least, they look like they are going to very quickly lose output by becoming covered in crud. Just the dust in the air combined with condensation in the morning will probably knock 20% or more off their output in no time.

I think you should find a way of supporting them in the middle to improve drainage and self cleaning.
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Old 22-08-2019, 16:40   #9
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Re: New Solar Installation - Odd Results?

The power out of the panels is going to be the same, series or parallel. In Series your voltage doubles in parallel your current doubles. Your panels are 24v panels but put out close to 30 volts. Series your at 60 volts make sure your charger will take that. If not go parallel and feed them parallel for 30v.
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Old 22-08-2019, 21:08   #10
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Re: New Solar Installation - Odd Results?

Quote:
Originally Posted by ohgary View Post
Your panels are 24v panels but put out close to 30 volts. Series your at 60 volts make sure your charger will take that. If not go parallel and feed them parallel for 30v.

Not a problem. He is in parallel so a max of 35V and 12.2A.



He also said he has a "Victron SmartSolar MPPT 100/30 controller" which is good for 100V and 30A so he has plenty of capacity whichever way he wires them.
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