How much oversizing is too much?

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sylk asked Feb 21, '23

How much oversizing is too much?

Hello everyone!

I am a newbie, currently i have an offgrid system in a cabin with 4 320wp solar panels with a blue solar 150-35. 48 volts, 4 x pylontech us2000c.

During 3 months of winter i have bad shading because of a tall hill nearby, so mostly indirect lighting. Unfortunately is the only option, no grid nearby.

I ordered 12 jinko solar 420wp (37.96Voc, 14.01Isc). I want to make 4 series x 3 in parallel.

When i checked "oversize 135%", Victron calculator recomended me my exact charger, 150-35, and it said 253% oversized.

I ll be happy to keep using it, but how good this is for my system? And what charger do you recommend instead?

Thank you!

MPPT Controllers 48v battery solar sizing

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Answer 1 · 2023-02-21T22:12:45Z

kevgermany answered · Feb 21, 2023 at 10:12 PM

It will be ok if the calculator signed off on it. But the configuration sounds wrong. Four parallel sets of three in series sounds safer. Otherwise the panels may exceed the MPPT max input voltage.

This makes me wonder if you entered some parameters incorrectly.

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Answer 2 · 2023-02-22T04:52:01Z

Alexandra answered · Feb 22, 2023 at 04:52 AM

@Sylk

As long as you dont break the rules of not exceeding the input voltage limit (at your lowest temperature- so temp are important) and the short circuit current for input (string combo), you can panel up. Good to slightly over panel for low light/irradiance, but a total waste in good sun otherwise.

You will be slightly over the isc on the 35A.

12 x 420W is 5040w at STC (assume thats the stats you are using) so at 48V you will need at least 100A mppt charger, so you dont peak shave in good light.

I would use 250/100. Or 250/85 if overpanel was the aim.

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Answer 3 · 2023-02-22T05:55:25Z

sylk answered · Feb 22, 2023 at 05:55 AM

Thank you for your answers!

I attached the pdf from the calculator.

If i am not mistaken, i won t be able to take full advantage of the entire array in the summer, but will it help in winter in low light conditions?

Also, will it be safe to run it like this for a couple months until i change the mppt?

mppt_calculator_2_22_2023, 7_43_43 AM.pdf

mppt-calculator-2-22-2023-7-43-43-am.pdf (721.9 KiB)

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JohnC ♦ commented · Feb 22, 2023 at 06:19 AM

@Sylk

You forgot the *minus* sign on the V Temp Coeff. You'll need to rerun it. Forget what you have now.

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sylk JohnC ♦ commented · Feb 22, 2023 at 06:29 AM

@JohnC Thank you! That was the problem! Now it correctly recommends me 150/85 for 3s 4p, and 250/85 for 4s 3p.

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Answer 4 · 2023-02-22T06:01:03Z

Michelle Konzack answered · Feb 22, 2023 at 06:01 AM

Good morning,

why not use a RS450/100 for it and use optimizers on the shaded panels?

This would boost the solar output enorm in the winter.

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nickdb ♦♦ commented · Feb 22, 2023 at 07:01 AM

As mentioned, optimisers are not supported, so please don't recommend things which aren't supported if you are unfamiliar with the products.

Also, the RS is a lot more expensive and way over the required spec.

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JohnC ♦ commented · Feb 22, 2023 at 06:23 AM

@Michelle Konzack

Victron don't recommend panel optimizers on their mppts. I can't speak for the RS, but unless you've seen it expressly stated that it's ok, then it's probably not.

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Michelle Konzack JohnC ♦ commented · Feb 22, 2023 at 06:30 AM

I am talking especially about this ones:

Huawei SUN2000-450W-P

Maybe someone @Victron can give us more info's. I use on one of my SmartSolar MPPT 250/100-Tr VE.Can two of them because two of the 6 panels get 1/3 shaded in the morning for around 3-4 hours.

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Michelle Konzack Michelle Konzack commented · Feb 22, 2023 at 06:32 AM

I am talking especially about this ones:

Huawei SUN2000-450W-P

Maybe someone @Victron Energy Staff can give us more info's. I use on one of my SmartSolar MPPT 250/100-Tr VE.Can two of them because two of the 6 panels get 1/3 shaded in the morning for around 3-4 hours.

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JohnC ♦ Michelle Konzack commented · Feb 22, 2023 at 06:56 AM

@Michelle Konzack

The official line from https://www.victronenergy.com/live/drafts:mppt_faq is..

There's also a few threads here you could chase down.

Not saying you couldn't make a particular type work, like if it were just on one panel string of several and Vmp outside the tracked range. Recommending it broadly perhaps not a good idea.

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1677048477773.png (5.5 KiB)

Answer 5 · 2023-02-22T06:46:42Z

nesswill answered · Feb 22, 2023 at 06:46 AM

I agree with the suggestions above (mostly), i use Smartsolar MPPT RS 450/100 x2 with one set to the panels @ 55/60degrease for winter sun facing due south (in some shade) and one set for summer sun @ 35/40degrease south/west (no shading issues).

If in shade / cloudy conditions you can produce enough WPh to cover your usage and charge your batteries a bit the rest will take care of its self.

You need to use what fits best your situation and what affordable to you.

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nesswill commented · Feb 22, 2023 at 08:50 AM

Here is what i get on a cloudy wet day in the uk when setup correctly (i think) to give you an idea for your setup.

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screenshot-20230222-084013-chrome.jpg (312.9 KiB)

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