MPPT fails to find MPP when partially shaded

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kadlecp asked Jan 22, '23

MPPT fails to find MPP when partially shaded

Hello,

I have a BlueSolar 150/70 MPPT solar charger controller.

There are 4 panels connected to it. Each is 450Wp having 120 cells. They are horizontally mounted on a flat roof in 2s2p configuration.

The problem is that when panels are partially shaded then solar output is much lower than expected.

Here is a graph from a winter sunny day.

Between 9:00 and 12:30 less than 2/3 of the panels are shaded, and from around 12:30 less than 1/3 of the panels is shaded.

Here is a simulation of how they are shaded at 12:30

It's a winter so I don't expect full 1800Wp peak power output but maybe around 1200Wp should be possible maximum.

With the bypass diod in the panels activated I would expect 2/3 of the maximum to be produced when less than 1/3 of the panel is shaded (~800W), but the reality is somewhere between 100W and 200W.

It's clearly visible that MPPT controller is trying to find maximum MPP every 10 minutes, but it's failing to do so.

Any idea what could be wrong? Incorrect configuration, wrong wiring, or something else?

MPPT Controllers

1674386277209.png (98.3 KiB)

1674388247792.png (148.2 KiB)

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klim8skeptic ♦ commented · Jan 22, 2023 at 08:48 PM

Any shading of a panel is bad. Depending on the construction of the panel, results of partial shade is unpredictable.

Andy tests a solar panel. Start at 8:00.

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kadlecp klim8skeptic ♦ commented · Jan 24, 2023 at 09:09 PM

Thanks for the link. But the shading of the shingled panels in the video seems predictable.

Mine are half-cell modules with 120 cells and from what I read, it suppose to have 3 sections connected in parallel and if one of the sections gets hard shadow then whole section is out of the game. Maybe the problem is that those shadows do not trigger bypass diods but the drop in current is still significant and therefore MPPT does not have too much to work with.

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Modifications Space

Node Red Space

Answer 1 · 2023-01-22T12:48:20Z

Stefanie (Victron Energy Staff) answered · Jan 22, 2023 at 12:48 PM

@kadlecp

I'm not 100% sure but I think it has to do with your panels and how they react to shading. For example, I have a 400Wp half-cell module that switches between two MPPs in partial shading. The second basically only delivers half the Vmp. The MPPT cannot do anything about that.

When I look at the diagram, it looks the same as mine.

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Answer 2 · 2023-01-22T21:29:32Z

gerard-van-seventer answered · Jan 22, 2023 at 09:29 PM

See also here

I think the generic mppt algorithm isn't suitable for all situations. Hence my question if the algorithm should be configurable so that we can finetune is to our environment.

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Answer 3 · 2023-01-23T06:00:01Z

nesswill answered · Jan 23, 2023 at 06:00 AM

Remember in the winter the sun is less than one quarter of its strength in the summer and depending on the angle of the panels you will only be looking at a very short time your panels are at the sweep spot (best angle v sun's hight in sky)

See solar energy

Hope this helps a bit...

Dave.

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Answer 4 · 2023-01-23T18:48:15Z

kadlecp answered · Jan 23, 2023 at 06:48 PM

Thanks all for the input.

I'm aware that winter sun hours and irradiation is much lower, but still it shouldn't be in the range of 100W - 200W at noon with full sun for 1800Wp. Also considering that at 13:30 it's as high as 500W.

I still think it must be either something with MPPT algorithm or strange behavior of the panels when shaded.

Is it possible that MPPT blocks bypass diods from being activated?

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nickdb ♦♦ commented · Jan 23, 2023 at 07:30 PM

MPPT’s do their job well. If you’re not getting what you expect, is has everything to do with either your panel choice or how they have been installed. Or both.

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Answer 5 · 2023-01-24T06:12:48Z

nesswill answered · Jan 24, 2023 at 06:12 AM

I have a similar setup on my x9 550w panels facing south @ 35 degrees, at this time of year some will be part shaded like yours, this time of the year i will get less than 1/4 of what i get in the summer. I also have x9 of the same panels facing south @ 55 degrees just to take advantage of the winter sun and this works well. I have a total of x30 panels facing different directions at different angles to ensure no matter what time of year i get a good all year round generation.

I have not seen any problem with the MPPT's i use, sorry i can not help.

Dave.

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Answer 6 · 2023-01-24T06:57:38Z

nesswill answered · Jan 24, 2023 at 06:57 AM

here is a basic example, top row @ 55 degrees, bottom @ 35 degrees (second in from left was a foggy day) the others where sunny. The other two trackers on the other MPPT was similar to the bottom row.

Note to other's i did say a basic example so please don't shoot me down... (yes i did get to 100% on each day)

Cheers Dave.

35-v-55.jpg (18.3 KiB)

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