adding a solar panel of different wattage

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overland asked Apr 29, '22

adding a solar panel of different wattage

Hello, I have an off grid system that is using the Victron MPPT 150/85 solar charge controller. On top of our RV we currently have four 300W Renogy Watt Monocrystalline Solar Panels. I would like to add another panel or two but Renogy is no longer making the 300W panel. They are now only making a 320 Watt panel. Can I add that to the array or because it is a different wattage would it be a problem? Would it be better to go with a different brand and stick to 300 Watt panels? My current 4 panels are running in Parallel going into the MPPT 150/85 solar charge controller. Please advise! I need more solar to run the Air Conditioner this summer. Thanks

Solar Panel

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Answer 1 · 2022-04-30T04:18:01Z

kevgermany answered · Apr 30, 2022 at 04:18 AM

Ideally, no, but if the new panel Vmpp is close to the existing panels, it will work, with some reduction in overall performance.

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Answer 2 · 2022-04-30T05:24:00Z

overland answered · Apr 30, 2022 at 05:24 AM

Thanks so much for the response.. I did a little research and learned that the Vmpp is the voltage when the power output is the greatest. I guess that would mean it would be better to use a different 300W brand of Solar panel rather than the upgraded 320W Renogy panel. I wonder if the reduction in performance would negate the gain of adding an additional panel? The Optimum Operating Current of my 300W panels is 9.32 A. and the Optimal Operating current of the upgraded Renogy 320W panels is 9.79A.

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Answer 3 · 2022-04-30T09:03:18Z

elvis answered · Apr 30, 2022 at 09:03 AM

Can you add your new panel's to an additional new smaller MPPT?

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Answer 4 · 2022-05-02T04:04:08Z

overland answered · May 02, 2022 at 04:04 AM

I couldn't easily do that. I don't have any room in the box where all the electronics are and I would have to run a lot of new wire down the wall. I was hoping to just be able to add at least one additional panel to what I already have as it would be so much simpler. Truth is I think the 320W Renogy panels are all sold out too now. It's crazy I can't find any 300W 24volt panels out there for sale.

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klim8skeptic ♦ commented · May 02, 2022 at 05:39 AM

305w Victron monos are pretty close ;).

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Answer 5 · 2022-05-02T22:57:08Z

overland answered · May 02, 2022 at 10:57 PM

nice. I tried to find an online dealer of the Victron panels 305W 24V but can't seem to find any of those either.

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kevgermany ♦♦ commented · May 03, 2022 at 05:34 AM

What are the Vmpp voltages of the old/new renogy panels

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Answer 6 · 2022-05-03T06:08:04Z

n-dee answered · May 03, 2022 at 06:08 AM

I did the same. working well.

I have these 325er modules:

and I added these 340er

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1651558059252.png (60.1 KiB)

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Answer 7 · 2022-05-03T22:55:46Z

overland answered · May 03, 2022 at 10:55 PM

The Optimum Operating Current of my 300W panels is 9.32 A. and the Optimal Operating current of the upgraded Renogy 320W panels is 9.79A.

1651618472889.png (203.4 KiB)

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klim8skeptic ♦ commented · May 04, 2022 at 01:06 AM

Looking at the data sheet I would think any mono panel with 60 cells ~ 300w would suit.

Second hand panels are cheap as. What country are you in?

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overland klim8skeptic ♦ commented · May 05, 2022 at 08:21 PM

I'm in California USA. I'm not sure where to find used panels but I will check ebay.

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Answer 8 · 2022-05-03T22:57:29Z

overland answered · May 03, 2022 at 10:57 PM

I can't clearly find the Vmpp listed on either product but I did find the max Amp output

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kevgermany ♦♦ commented · May 04, 2022 at 05:22 AM

I just downloaded a Renogy data sheet for the 24V 300W panel. They use the term Optimum operating voltage with the abbreviation Vmp. It's the same as Vmpp. Sorry for the confusion.

A little background. The MPPT adjusts itself to draw max power by adjusting the resistance the panels the panels push against. In parallel wiring, the voltages must match/be close In series the currents must match/be close.

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Answer 9 · 2022-05-04T04:49:30Z

Paul B answered · May 04, 2022 at 04:49 AM

if you are connecting in parallel then the the same OCV is quite important as the MPPT use this but if its within say 5% it should be fine.

now if you go to series string then the amps must all be the same (or close ) and voltage does not matter.

if its on top of a van then series would be better overall as you get more out of the panels in the mornings and evenings and more on cloudy days, and as there would be no shade on average on the panels you should be fine.

so sum the OCV voltage of all the panels and then make sure that that figure is LOWER than the max voltage for your MPPT unit.

there are lots of different ways of doing setups for diferant reason - so maybe find a good solar shop that can advise you on your best senario for your van - good advise now could save you a ton of money latter.

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Answer 10 · 2022-05-05T20:27:41Z

overland answered · May 05, 2022 at 08:27 PM

can anyone tell me the max voltage of the Victrom MPPT 150/85? Assuming that I keep them all in Paralle I would need to find another panel that has a optimum Voltage within 5% of 32.2 Volts right? Any suggestions on where to find a panel like that new or used. I've been searching with no luck.

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