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Solar panel Voc and capacity issues


neillherbst

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Hi All

I'm currently trying to determine whether I have an issue with my solar panels. The initial installation was supposed to be 12 x 460w (5.5 kw) panels, however, I'm contantly getting closer to 4kw total. The panels are arranged in 2 strings of 6 panels each.

My rooftop is due north at a 30° angle and there are no trees that can cause shading issues in the middle of the day.  

Is this normal to see such a big deviation from theoretical capacity? I'm not 100% sure what panels I have but I know they are Qcell with a black finish. According to some of the datasheets you would expect a Voc of about 50v per panel at normal operating conditions. Therefore the total Voc per string should be about 300V however when I measure it it is only around 244V per string? The math tells me this is closer to 5 panels per string. 

 

Could it be possible that the installer installed panels of smaller capacity? Or could it be a connection issue? Or maybe it is what is expected in a typical setup.

 

Thanks in advance.

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Winter is not the best time to be honest as the sun angle is lower - so we are all suffering in terms of PV production. I am topping out at 4kw on a 6kw install for example. If in doubt ask installer to come back  and prove the panel wattages and recheck connections

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Okay so here an example of 460W sort of close to what you mentioned above:

Standard Conditions:

image.png

*** What they sell = 6s2p = (6 x 44.89) x (2 x 10.25) = 269.34 x 20.5 = 5.521kW

Normal (including it is winter now, so might even be less)

image.thumb.png.3174e5c055db35ee12a0d4086fce411f.png

Truth:

6s2p = (6 x 42.64) x (2 x 8.08) = 255.84V x 16.16A = 4.134kW

 

Edited by Eurard
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This is essentially what I have installed. I climbed on the roof and verified the panels.

The Voc still bothers me a bit though but I the calculation of the normal operating conditions essentially matches what I am seeing. Just a bit shocked that the actual vs nominal performace is so vastly different.

Edited by neillherbst
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27 minutes ago, Eurard said:

Okay so here an example of 460W sort of close to what you mentioned above:

Standard Conditions:

image.png

*** What they sell = 6s2p = (6 x 44.89) x (2 x 10.25) = 269.34 x 20.5 = 5.521kW

Normal (including it is winter now, so might even be less)

image.thumb.png.3174e5c055db35ee12a0d4086fce411f.png

Truth:

6s2p = (6 x 42.64) x (2 x 8.08) = 255.84V x 16.16A = 4.134kW

 

This is essentially what I have installed. I climbed on the roof and verified the panels.

The Voc still bothers me a bit though but I the calculation of the normal operating conditions essentially matches what I am seeing. Just a bit shocked that the actual vs nominal performace is so vastly different.

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15 minutes ago, neillherbst said:

This is essentially what I have installed. I climbed on the roof and verified the panels.

The Voc still bothers me a bit though but I the calculation of the normal operating conditions essentially matches what I am seeing. Just a bit shocked that the actual vs nominal performace is so vastly different.

I hear you, but you can expect less this time of year by easy 35%, depending might even be less if hazy etc etc.

If you get that currently you should get what you paid for when the sun gets stronger again.

You at least have real world problems and dont sit with a max gain of 1kW from 5000W worth of panels on the roof, buying a complete dud, but they will be utilized somewhere for something when I in the future get proper panels.

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1 minute ago, Eurard said:

I hear you, but you can expect less this time of year by easy 35%, depending might even be less if hazy etc etc.

If you get that currently you should get what you paid for when the sun gets stronger again.

You at least have real world problems and dont sit with a max gain of 1kW from 5000W worth of panels on the roof, buying a complete dud, but they will be utilized somewhere for something when I in the future get proper panels.

I would much rather take my problems over yours lol. Thanks for the help and explanation.

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