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Old 21-02-2018, 06:22   #1
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Solar 4x4 cell grid wiring (is this logical?)

Dear CF community,

I am sure everyone has had enough series vs parallel wiring discussion, but here is a tricky and interesting one. Let's enter the matrix...

I like to set up a 4x4 grid out of 50 Watt cells. Each cell has a bypass diode included. Is should be small cells to achieve suffiecient string voltage for charging my 48V battery system efficiently. After "Gone with the Wynns" educated us about the effects of shadowing I wonder how to wire the cells up. Should it be 4 series strings in parallel or 4 parallel strings to get one series string?

My goal is to have good output even with a possible diagonal or straight boom shadow. First parallel seems to be far superior. Can someone confirm that there is no logical mistake?

For easy discussion I made a drawing of the two options with my assumptions.


Any advice would be appriciated.
Thanks,
Peter
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Old 21-02-2018, 07:49   #2
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Re: Solar 4x4 cell grid wiring (is this logical?)

First Q why 48V?

I would **start with your solar controller**, which you don't even mention here.

Is it a pricey fancy unit or a cheapie like MPT-7210A*?

The simplicity of a 1:1 ratio with a reasonably priced SC will best handle partial shading, each panel optimized individually by its own MPT calculation.

The key to value is buying the panel to maximize the SC's output, that includes finding panels in the optimum voltage range to suit the SC, so no need to serial multiple small ones.

The input voltage from the panels maybe a completely separate issue from the bank voltage.

IMO also consider the option of overpanelling.
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Old 22-02-2018, 03:41   #3
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Re: Solar 4x4 cell grid wiring (is this logical?)

48V is needed because of 2 10kw electric drives. More would even be better.

I expect 4x 200 Watt panels to be much more impacted by shadowing because of the overall lower number of bypass diodes in the system than using 16x50W. (Warning assumption!) Also they would need to be run in series to achieve a good voltage for charging 48V. With any full cell shadow on any panel this would lead to no power output at all.

Sure a quality controller is mandatory. But at the end what the controller will see is different Power over Voltage (P-V) curves for both wiring options. Actually this P-V curve is the sum each single P-V curve of all cells. But which one is better (=higher)?

Let's assume the controller will always find the MPP and track it: What will be the more robust wiring in terms of partial shadowing?
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Old 22-02-2018, 05:39   #4
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Re: Solar 4x4 cell grid wiring (is this logical?)

Dear all,

luckily I found a thesis dealing with this question:
Modeling and Reconfiguration of Solar
Photovoltaic Arrays under Non-Uniform Shadow
Conditions by
Dung Duc Nguyen

https://repository.library.northeast...2/fulltext.pdf

The two setups are called Series-Parallel (SP) and Total-cross-tied (TCT) arrays. See page 44ff.

Simulation results (page 60ff) cleary show that the TCT (=4 parallel 1 series) has higher output over the whole range of non uniform shading configurations.

This setup should be superior to any setup with a smaller amount of stronger panels. There the small shadows would cause more power damage. Assumption seemed to be right.

Feels like I entered this forum by just talking to myself. Hope you enjoyed.
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Old 22-02-2018, 05:45   #5
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Re: Solar 4x4 cell grid wiring (is this logical?)

Quote:
Originally Posted by PeterSch View Post
I expect 4x 200 Watt panels to be much more impacted by shadowing because of the overall lower number of bypass diodes in the system than using 16x50W.
Not if you can get to 1:1 SC/panel ratio, where partial shade has zero impact on any other panels.

Diodes have a power cost, while each panel getting a separate MPP is a boost in overall output.

Quote:
Originally Posted by PeterSch View Post
Also they would need to be run in series to achieve a good voltage for charging 48V.
Why? I'm talking about going to single larger panels with a higher VoC, say 70-120V.


Quote:
Originally Posted by PeterSch View Post
What will be the more robust wiring in terms of partial shadowing?
Easy enough to A/B test at commissioning time.
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Old 22-02-2018, 05:51   #6
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Re: Solar 4x4 cell grid wiring (is this logical?)

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Sure a quality controller is mandatory.
My point is to select a relatively inexpensive SC (within your "quality" requirement, say features required)

And then select the panel by Watts and Voltage to optimize the SC output at a 1:1 panel ratio.

For example, Victron 150/30, look for a 100-130 VoC panel in the say 4-500W range.

The exact model of SC being your starting point, not an afterthought.
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Old 22-02-2018, 08:02   #7
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Re: Solar 4x4 cell grid wiring (is this logical?)

Quote:
Originally Posted by PeterSch View Post
I expect 4x 200 Watt panels to be much more impacted by shadowing because of the overall lower number of bypass diodes in the system than using 16x50W. (Warning assumption!)
I would look at the actual bypass diode configuration of the various panels. For example, the two different 100W panels I am familiar with have two bypass diodes per panel. I have seen larger panels with three or more bypass diodes (panels are effectively cut into multiple shorter series-cell string sections, with a bypass diode for each section). There will be no advantage to a smaller panel if it has only one diode.

That is an interesting study you found, but it appears that the author is assuming one bypass diode per panel (I just skimmed the paper, I could be wrong).
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Old 22-02-2018, 08:05   #8
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Re: Solar 4x4 cell grid wiring (is this logical?)

Quote:
Originally Posted by PeterSch View Post
Dear CF community,

I am sure everyone has had enough series vs parallel wiring discussion, but here is a tricky and interesting one. Let's enter the matrix...

I like to set up a 4x4 grid out of 50 Watt cells. Each cell has a bypass diode included. Is should be small cells to achieve suffiecient string voltage for charging my 48V battery system efficiently. After "Gone with the Wynns" educated us about the effects of shadowing I wonder how to wire the cells up. Should it be 4 series strings in parallel or 4 parallel strings to get one series string?

My goal is to have good output even with a possible diagonal or straight boom shadow. First parallel seems to be far superior. Can someone confirm that there is no logical mistake?

For easy discussion I made a drawing of the two options with my assumptions.


Any advice would be appriciated.
Thanks,
Peter
All parallel is the best Option. Use some cheep MPPT step-up converter.

https://de.aliexpress.com/item/MPT-7...693879749.html

Input Voltage: 12-60V Output 24-72V / 10A
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Old 22-02-2018, 10:33   #9
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Re: Solar 4x4 cell grid wiring (is this logical?)

Check out Pacific Yacht Systems series on setting up solar on YouTube. His company does hundreds of these installations. He is an Electrical Engineer and a boater. The information in his YouTubes is invaluable on all the factors of setting one of these up.



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Old 22-02-2018, 12:28   #10
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Re: Solar 4x4 cell grid wiring (is this logical?)

Using a cheap boost converter

especially **instead of** a proper charge controller (is that what you meant, really??)

will not be nearly as effective, very crude and inefficient setup.

but also just in addition to a SC

will consume quite a bit of its power output.


DC-DC voltage conversion is a small part of what even the cheapest MPPT SC does, and should be designed by the SC engineers as integral to that overall functionality.
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Old 22-02-2018, 12:40   #11
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Re: Solar 4x4 cell grid wiring (is this logical?)

Quote:
Originally Posted by john61ct View Post
Not if you can get to 1:1 SC/panel ratio, where partial shade has zero impact on any other panels.

Diodes have a power cost, while each panel getting a separate MPP is a boost in overall output.

Why? I'm talking about going to single larger panels with a higher VoC, say 70-120V.


Easy enough to A/B test at commissioning time.
Do you have a reference to such panels?
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Old 23-02-2018, 00:32   #12
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Re: Solar 4x4 cell grid wiring (is this logical?)

AUO BenQ Solar SunForte PM096B00 330 Watt - 96 Cells,


Power (Wp): 330
Vmp (V): 54,7V
Imp (A): 6,04A
Isc (A): 6,52A
Voc (V): 64,9V
max string Voltage (V): 1000
STC: 20,3%
Cell-Type: 96 high-efficiency back contact cells
Tolerance: 0/+3 %
Size (LxWxH) (mm): 1559 x 1046 x 46
Weight (kg): 18,6
Cells: 96
Connector: MC4 connectable
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Old 23-02-2018, 00:37   #13
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Re: Solar 4x4 cell grid wiring (is this logical?)

Quote:
Originally Posted by john61ct View Post
Using a cheap boost converter

especially **instead of** a proper charge controller (is that what you meant, really??)

will not be nearly as effective, very crude and inefficient setup.

but also just in addition to a SC

will consume quite a bit of its power output.


DC-DC voltage conversion is a small part of what even the cheapest MPPT SC does, and should be designed by the SC engineers as integral to that overall functionality.
It will be even then more efficient than the grid wiring above with the 50Wp cell modules. If you want a professional setup, dont use cheep 50Wp panles, use a professional panel and a professional controller.
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Old 23-02-2018, 02:51   #14
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Re: Solar 4x4 cell grid wiring (is this logical?)

You may want to check out the AltE website. They have many videos on their site that are very helpful.
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Old 23-02-2018, 09:23   #15
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Re: Solar 4x4 cell grid wiring (is this logical?)

The 50-60Voc range seems more common these days at the order-online suppliers, which should be fine to give MPPT a decent working range.

It's the wattage output you want to get right up near SC's max, or a bit past for overpaneling if the price is right.

The fact OP is looking for 48V output means most SCs will be very expensive, personally I'd try that DROK MPT-7210A first

https://m.banggood.com/MPT-7210A-Alu...p-1056572.html

pdf http://www.yampe.com/images/pdf/2907.pdf

see what kind of charging power it delivers boosting from a single appropriately matched panel, maybe a nominal 24V one, should be 38-46Voc, this SC only talks about Boost conversion not Buck, so don't go too high.

Those should also be easier to find, maybe even Grape / Renogy mass-market if local opportunities aren't cheaper.

Repeating, the goal here is 1:1 panel per SC for best partial shade handling, max say 400-550W per pair. Going so cheap means you can carry spares.

If you want to go fancier choose the SC first and we can help identify a panel that helps maximize its output.
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