PV low (~half) wattage into MPPT during bulk

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elijahnotfound asked Jul 5, '23

PV low (~half) wattage into MPPT during bulk

I am receiving lower voltage and current than expected when panels are connects to my MPPT 100/50. Full sun.

4 x 150w Panels (Voc = 20.9, Isc = 9.39) each tests around 20 volts and 5.5 amps when not connect to the MPPT.

Here is the reading for the whole system as diagrammed. When not connected to the MPPT each pair of panels in series reads 40V. The power is about half of expected.

For simplicity I also tested just one panel to the mppt through the fuses and breaker. Reads 20V at the leads before connecting them into the MPPT, however when connected the voltage reads at 15 and I get about half the expected current in bulk:

Is there something I am missing that I can test? Could this be an MPPT hardware issue? Thanks for the help!

MPPT Controllers Solar Panel voltage power

screenshot-2023-07-05-124029.png (22.6 KiB)

screenshot-20230705-114009.png (127.9 KiB)

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Answer 1 · 2023-07-05T16:49:55Z

mvas answered · Jul 05, 2023 at 04:49 PM

Do you think your input voltage is too low?
Hint: read the manual.
What if ... all panels are connected in SERIES?

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elijahnotfound commented · Jul 05, 2023 at 05:07 PM

The voltage of one panel is 20v measured. The voltage in 2series/2parallel is 40v measured. Both meet the threshold of "5V above the battery voltage" as stated in the manual.

Hint: read the post.

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mvas elijahnotfound commented · Jul 05, 2023 at 05:16 PM

I read your post.
Another hint - Your Voc is irrelevant when using your MPPT controller.
Again, read the manual regarding input voltage.

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elijahnotfound mvas commented · Jul 05, 2023 at 05:21 PM

Check out the screenshots. Well above the "5V" threshold, still only about half the expected power. I've read through the manual and have not found a solution, hence why I'm posting here.

If you're here to help people, you can probably work on the tone. I'm not here claiming to know everything hence why I'm asking questions. If you're here just to be rude, hint: try Twitter instead.

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Answer 2 · 2023-07-05T17:15:27Z

elijahnotfound answered · Jul 05, 2023 at 05:15 PM

Here is the reading for the whole system as diagrammed. Again, when not connected to the MPPT each pair of panels reads 40V.

screenshot-20230705-131309.png (135.5 KiB)

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Answer 3 · 2023-07-05T17:41:00Z

kevgermany answered · Jul 05, 2023 at 05:41 PM

Let's get this on track.

If your panels aren't reaching Voc in full sun, then they're not going to deliver full output. The panel specs are for 25C and pretty high irradiance. The lower voltage suggests you're not getting the light you think you are.

To give you an example, my system with 600W panels gives a max of about 500W in the South of Germany, but not much more than half of that in the UK.

Series/parallel connection may help, especially at the ends of the day and when it's very cloudy.

Solar panels have a big voltage drop under load and with lowish light. The MPPT will optimise it's draw from the panels, based on the max power it can get from them, not based on voltage. Your drop from 20 to 15V suggests that there's not enough light to fully drive the panels, but the MPPT is doing its best.

There are some web sites around that will give estimated solar yields by geographical location.

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elijahnotfound commented · Jul 05, 2023 at 05:53 PM

I appreciate the input. However, I am reaching Voc of 20 across each panel when measured and NOT connected to the MPPT (Voc of 40 across the pairs in series).

Full sun, perfect solar conditions. I don't anticipate squeezing every watt of the optimal 600, but I am receiving less than half of it in near perfect conditions.

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Answer 4 · 2023-07-05T19:07:32Z

elijahnotfound answered · Jul 05, 2023 at 07:07 PM

Haven't solved the issue but a little bit of an unfortunate update:

The 4 x 150w panels are most likely 120w panels. I should have done a bit more research given the dimensions, but after testing everything for this post and getting about 110w from each of them isolated, I have a strong feeling they are not 150w panels.

That being said, I am still nowhere near the 400w + that I should be getting at the controller and I can't account for the difference.

1688583877105.png (188.2 KiB)

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kevgermany ♦♦ commented · Jul 06, 2023 at 09:14 AM

18*8.34 is 150W.

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elijahnotfound kevgermany ♦♦ commented · Jul 06, 2023 at 11:48 AM

That is the spec listed for the panels, but they aren't operating near that. Additionally, if they were 150w given their dimensions, they would have an efficiency rating of 24.2% which is VERY high.

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pwfarnell commented · Jul 06, 2023 at 10:08 AM

How are your panels mounted, are they flat or angled to the sun, are they clean, are they on a surface which allows cooling air to flow over them or under them. My boat in UK midlands with 700W of panels flat on the roof without a space underneath normally peaks at 450W and at most I have seen 600W usually after a rain shower in full sun.

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elijahnotfound pwfarnell commented · Jul 06, 2023 at 11:49 AM

They are clean. They are also flat, so I do expect that to impact the production somewhat (although I'm not sure how much). We are close to peak sun angle of the year so hopefully it is somewhat mitigated.

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Alexandra ♦ elijahnotfound commented · Jul 06, 2023 at 12:00 PM

They are rated at 1000w/m² STC as is every other panel. If you don't (and you are not likely to) have that kind of irradiance, then you won't get the power shown on the sticker. Even less if the panels are warmer than 25°C.

You are testing 5.5A from a potential 8\9A. so your irradiance is at about 60%

600 x 60% is 360w if your panels are 25°C. They are likely hotter since they are flat so even less power.

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Alexandra ♦ Alexandra ♦ commented · Jul 06, 2023 at 12:07 PM

Is there a reason why you didnt run them in a string of 4 panels rather than 2s 2p?

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elijahnotfound Alexandra ♦ commented · Jul 06, 2023 at 12:28 PM

There were two reasons. The first, according to a calculator the temperature compensated array voltage could peak at 108V, which would make my 100/50 inadequate. Second, I wanted to preserve some of the power generation if one of the panels happened to be slightly shaded.

I don't imagine four in series would account for too significant a difference would it?

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Alexandra ♦ elijahnotfound commented · Jul 06, 2023 at 12:49 PM

The start and end voltage is affected, so longer 'solar' days.

What temp compensation coefficients were you entering? And low temps like colder than -20°C?

It is unusual for 86.4voc to reach to 100voc at least in my experience. (I haven't installed everywhere in the world though.)

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elijahnotfound Alexandra ♦ commented · Jul 06, 2023 at 01:10 PM

Ah that makes sense with the start and end voltage! Didn't think about that - may reconsider the layout in that case to catch a bit of extra charge time.

Battleborn recommended no temperature compensation so I kept that off.

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elijahnotfound Alexandra ♦ commented · Jul 06, 2023 at 12:33 PM

the 5.5A is when the panels are disconnected from the controller. When connected to the controller they drop to about 5A and the voltage across them drops from 20V to 15V. I'm really just trying to figure out if this difference between connected/not connected is expected.

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pwfarnell elijahnotfound commented · Jul 06, 2023 at 02:34 PM

When you measure the voltage with a multimeter the current flow is very small so the voltage goes to maximum and the power produced is near to zero. However, when you start drawing power, the voltage reduces below the maximum and current increases. My voltage max is about 80V but when running it is around 65V.

From what has been shown there is nothing wrong with your Victron controller, you have panels that are perhaps optimistically rated and you are seeing the normal production being lower than spec as we rarely see the rated irradiance whilst panels remain cool.

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Answer 5 · 2023-07-06T05:28:26Z

Graham Owens answered · Jul 06, 2023 at 05:28 AM

What are your battery settings? What is your charge current limit set to?

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elijahnotfound commented · Jul 06, 2023 at 12:24 PM

Battery settings set to default LiFePo4 with current limit set to the default hardware limit of 50a.

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Answer 6 · 2023-07-07T11:22:03Z

pln answered · Jul 07, 2023 at 11:22 AM

Hello, I'm facing exactly the same issue!

New 110W ETFE flexible panel, Bluesolar MPPT 75/15

I measured and tested the panel with the optimal beam angle, at the best hour (sun at the zenith), without clouds, but the power is half the nominal value.

Measurement: Voc 22V, Isc 5,2A

Official value from sticker: Voc 23,4V Isc 6,14A Pmax 110W Vmp19,5V Imp 5,64A

(batterie settings and charge current checked)

But the Victron only outputs 55W maximum. It should be more.

Can we imagine a software or hardware issue of the controller?

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elijahnotfound commented · Jul 08, 2023 at 06:03 PM

Unfortunately I haven't had much luck.

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kevgermany ♦♦ commented · Jul 08, 2023 at 06:29 PM

Like @elijahnotfound you're not seeing the sticker values on the panel. So either too little light (most likely) or faulty/oversold panels.

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