Quick MPPT Nominal PV Power Question

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winnie asked Apr 30, '21

Quick MPPT Nominal PV Power Question

I'm looking to purchase a Victron SmartSolar Charge Controller 250/100.

I currently have six 12v lithium batteries and four 24v 320w solar panels (4×320=1280 total watts). The 250/100 manual states that the Nominal PV Power for a 12v is 1450 W and that the Nominal PV Power for a 24v is 2900 W.

My question before purchase: Since my solar panels (PV) are 24v, does that mean I could increase my solar panel total wattage up to 2900 W or is it capped at 1450 W because of my 12v batteries running a 12v house electrical system?

To avoid confusion, please note that I DO understand that I would also need to stay under the Maximum Open Circuit Voltage of 250 V (that maximumPV wattage isn't the only concern) and that the SmartSolar Controller is capable of converting 24v PV to 12v batteries.

Thanks for your time. I can't afford to make a mistake here, so I just want to be sure that I can add more 24v solar panels in the future.

MPPT Controllers MPPT SmartSolar

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jackyben answered · May 06, 2022 at 01:51 PM

Thanks to Matthias I now understand where the nominal PV power values come from. However going back to the original question from Winnie and the screen shot of the specifications. Where it says "Nominal PV power, 24V 1a,b)"

The footnote 1a (see above) says that the MPPT can handle more power. And I understand the limit of the voltage and max current to the MPPT. I want to know how much more power? By adding extra strings, one can stay within the voltage and current limitations, but still have substantially more power installed. One might want to do this if one wanted to extend the charging hours in a day. I want to know if there is an ultimate limit to the installed panel power, or if one just observes the limitations applicable to the current and voltage inputs, one can install whatever power is desired.

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wkirby ♦♦ commented · May 06, 2022 at 02:35 PM

There is no real limit to the amount of PV power that you install in front of the MPPT. It will take as much power from the array that it can until the limit of the output are met, either 100A battery current or Absorb Voltage limit.

More PV power will help on cloudy days and also, as you say, extend the day a little bit more. There is a sensible limit though, too much more becomes wasteful and at that point you should think about splitting the array into two separate controllers.

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Answer 1 · 2021-04-30T00:13:24Z

rslifkin answered · Apr 30, 2021 at 12:13 AM

The nominal wattage is based on battery voltage. A 250/100 can output up to 100A to the batteries regardless of panel voltage. For future growth, you can always add a second controller.

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winnie commented · Apr 30, 2021 at 02:11 AM

Thanks, rslifkin. The 100A output limit to the battery is certanly important information. For those unfamiliar, the second number on a Victron MPPT is the max output from the solar controller to battery(ies). So 250/100 denotes a 250V Open Circuit Limit and a 100A output max from the solar controller to batteries.

My original question could have been better worded. To clarify, I've included a screenshot of the Nominal PV Power information from the 250/100 manual. I'd like to know if I can add up to 2900W in PV on one 250/100 solar controller so as to minimize the cost against buying another expensive solar controller. As a reminder, my solar panels are 24V but my batteries are 12V (as is the AC inverter I was given).

I really appreciatet any help. Thanks.

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Matthias Lange - DE ♦ winnie commented · Apr 30, 2021 at 06:09 AM

The panel voltage doesn't matter. You have max. 100A to the battery.

100A x 14,2V (absorption voltage of the most LiFePO4 batteries) = 1450W

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winnie Matthias Lange - DE ♦ commented · Apr 30, 2021 at 12:53 PM

Thanks a lot, Matthias! You're been a big help.

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winnie Matthias Lange - DE ♦ commented · Apr 30, 2021 at 12:57 PM

I'm new to this forum and I can't quite figure out how to select the answer Matthias gave as the accepted answer to this question. Also, I don't see an option to reward Matthias with reputation points. I'll keep trying. Regardless thank you, Matthias!

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Matthias Lange - DE ♦ winnie commented · Apr 30, 2021 at 01:29 PM

That's because it is a comment to rslifkin's answer but his/her answer is also right.

But if you want I can convert my comment to an answer.

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winnie Matthias Lange - DE ♦ commented · Apr 30, 2021 at 11:30 PM

Thanks for the explanation. If you'd like the reputation points, then you could convert your comment to an answer. If reputation points don't matter to you, maybe just leave it as is since any reader will be able to follow along regardless. Thanks, again.

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Answer 2 · 2022-05-06T15:11:43Z

jackyben answered · May 06, 2022 at 03:11 PM

Thank you wkirby! One more question. Does this "unlimited" PV power ability also apply to 2015 Blue Solar MPPT's? I don't see the foot note in the manuals there. (I have a client with one) or is it an upgrade to the more modern Victron MPPTs?

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