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robby avatar image
robby asked

How to calculate ideal position for 3 solar panels

Hi,


I have 3 solar panels 225 Wp and a 100/30 victron smart solar mppt.


Panels:


Voc: 36,7V

Im: 7,53A



The panels are second hand and come from a big factory roof. So efficiency could be -10%.


The question I have is:


How can I calculate the best setup for the 3 panels? Will all three panels to the south give me the most yield or could it also be that 1 panel to SE, 1 to E and 1 to SW gives the best yield?

The voltage of all 3 panels in series would just exceed the 100V parameter so that is no option for this controller. But maybe that's an option with different wind direction per panel?


And after reading some information it seems that parallel is the way to go of you connect panels with different wind directions or different shading?


Hopefully someone can shine some light on this :)


Thanks in advance


setup
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robby avatar image robby commented ·
Thanks @kevgermany for the answer.


Can you elaborate a little more on what the "fighting" means?

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kevgermany avatar image kevgermany ♦♦ robby commented ·
With uneven illumination, the optimum MPPT settings are a compromise between what works best for each panel. This lowers overall output.

It's why big commercial installations are rows of panels with identical alignment. Then they all need the same treatment by the MPPT.


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3 Answers
kevgermany avatar image
kevgermany answered ·

Parallel is the only way here.

Panels should all have the same illumination. Otherwise they fight the controller and output is reduced.

Wind has no effect, unless you're thinking of cooling the panels. (Output reduces with heat).

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robby avatar image
robby answered ·

Alright I understand the serie vs parallel.


But how can I calculate the difference between:


The yield of power of all 3 panels facing south in parallel VS serie? Is it the same yield but only better in series because of higher voltage so smaller wires?


The yield of the 3 panels in series facing south or the 3 panels in parallel facing se, s, SW?


Thanks

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kevgermany avatar image kevgermany ♦♦ commented ·

Should be about the same as long as your voltage is high enough to initiate & maintain charge. But with your panels and controller, you must wire in parallel.See also @nesswill comment.

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nesswill avatar image nesswill commented ·

I can only speak from what i have found with x6 550w panels facing SSE.

In 3s2p better if shade falls on one set of 3

In 6s better if no sun, higher v = higher watts.

In full sun not much difference.

But what i have found for sure is the higher panels volts above battery volts the more watts you get.

As for the direction in full sun i have not noticed much difference until the angle of the sun to the panels get to about off full face by 60% then the power will drop off quickly.

But as i say this is just my experience others may have differing views.

Good luck.

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kevgermany avatar image kevgermany ♦♦ nesswill commented ·
The increased output with higher voltages is interesting. I'd love to see something definitive. Plenty of people say that higher voltage difference reduces output. But your experience clearly different.
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nesswill avatar image nesswill kevgermany ♦♦ commented ·

Here is a quick example of watts & volts same panels (x6 550w) with no sun facing the same direction.

Tractor - F is 3s2p

Tractor - R is 6s

6x6.jpg

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6x6.jpg (161.1 KiB)
Jason - UK avatar image
Jason - UK answered ·

@Robby

Below is a link to a helpful PV generation calculator. You can input the angle, tpye and so on, to work out the generation.

https://re.jrc.ec.europa.eu/pvg_tools/en/


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