33 Cell vs 36 Cell 100 Watt 12v Panels

[featherlite]

I currently have six 100 watt 12v Renogy Mono panels with the specs below: note 36 cells per panel.

I am looking at buying some 12v Rich Mono panels with the specs below: note 33 cells per panel.

I currently use a pair of Bogart PWM charge controllers.

I want to add more panels and upgrade to a Victron MPPT system and also want the flexibility of connecting the panels in various series-parallel configurations.

The Rich panels are the only panels I can find that match the existing Renogy volts and AH, and my physical size requirements. Moreover, the Rich panels are the only panels I have found that have 12 AWG wires rather than 14 AWG wires. My old Renogy panels have 10 AWG wires.

Question: Will the 33 cell Rich panels pose a problem?

PS: I still do not know if the Rich panels have any diodes. My research is ongoing.

Thank you for any input you can provide!

 

[sunshine_eggo]

In parallel, they will have no problem.

In series, the Renogy will force the Rich to operate at a slighly lower current.

IMHO, those panels are very well matched.

 

[RCinFLA]

For MPPT controller, if you are placing panels in series so the Vmp is moderately above battery voltage there is no problem.

Do not use a 32 or 33 cell panel, single or multiple in parallel if you intend to use an MPPT charger on a four-cell stack 12v LFP battery array. You need at least a 36 cell panel for this, or run two or more 32/33 cell panels in series.

There is roughly 0.45v to 0.5v per cell Vmp contribution depending on panel temp. MPPT controller requires some overhead voltage above battery voltage to work properly. Some of the overhead is for the DC to DC converter, some of the overhead is to allow the controller to search for MPPT point. 32 or 33 cell panel is okay for a PWM controller on 12v battery.

Most MPPT controllers will just drop into PWM mode operation if they cannot establish a reliable MPPT point but panel Voc is still above battery voltage.

 

[featherlite]

Thanks for the replies.
Due to my slow wittedness, I need more time to think about what is being said.
In the meantime, I am hoping you guys comment on each other's posts so that I can better understand.

Thank you!

 

[sunshine_eggo]

For MPPT controller, if you are placing panels in series so the Vmp is moderately above battery voltage there is no problem.

Do not use a 32 or 33 cell panel, single or multiple in parallel if you intend to use an MPPT charger on a four-cell stack 12v LFP battery array. You need at least a 36 cell panel for this, or run two or more 32/33 cell panels in series.

There is roughly 0.45v to 0.5v per cell Vmp contribution depending on panel temp. MPPT controller requires some overhead voltage above battery voltage to work properly. Some of the overhead is for the DC to DC converter, some of the overhead is to allow the controller to search for MPPT point. 32 or 33 cell panel is okay for a PWM controller on 12v battery.

Most MPPT controllers will just drop into PWM mode operation if they cannot establish a reliable MPPT point but panel Voc is still above battery voltage.

Normally I would agree with you, but the panel performance values are almost a perfect match.

 

[RCinFLA]

Normally I would agree with you, but the panel performance values are almost a perfect match.

You are comparing apples and oranges specs. One is for 25 degs C panel, one is for 47 degs C panel.

33 x 0.564v = 18.6v Vmp for a silicon mono cell is not possible unless cells are held to 20 degs C. The Rich spec claims 25 degs which is not realistic with sun panel heating. Maybe in wintertime cold temps. At 47 degs C, which is still relatively low panel temp with sun panel heating it would be 0.516v x 33 = 17.0v Vmp, not the 18.6v listed in their spec.

Renogy 2017 lists 18.6v Vmp for 36 cell panel and their spec is for 47 degs C +/-2 degs. That will have about 0.516v Vmp at 47 degs C x 36 cells is 18.576v which matches their spec pretty well.

Monocrystaline cells

 

[featherlite]

RCinFLA and Sunshine,

Thank you for all of your input.

RCinFLA,

Are you saying that you doubt that the Rich panels would actually perform in accordance with the Rich specs but that the Renogy panels possibly could perform in accordance with the Renogy specs?

 

[foggysail]

OK... sorry, I have not read all of the above because of time restrictions but I do have some comments.

All so called 12V panels that I am familiar with have an open circuit voltage of about 21-22 VDC and Vmp is usually around 18V.

There are good reasons to wire panels in series and that is to minimize the voltage drop in the wires between the panels and the controller. I strongly recommend the OP avoid the pulse width modulation style controllers. MPP controllers are now affordable and allow putting panels in series. The only caution one needs is to understand the so called safe voltages are those below aobut 45V. Think old telephone systems with 48 VDC huge batteries.

I wired my panels (33v) 2 in parallel in series with another 2 in parallel for my boat. Sure, I can get voltages above 70 but I can also get by with almost no voltage drop in the wiring between my total 1190W panels and my Victron controller with two strings of #10 wire.

 

[featherlite]

Thanks for all the helpful replies.

I have an existing lead acid battery bank and believe that my Bogart PWM system was the best system for my lead acid batteries. I am now building a 560 Ah Lifepo4 battery bank and will be installing Victron charging and monitoring components.

Given that Rich solar never replied to my inquiry about whether their 33 cell panels have diodes, and given the uncertainty respecting the actual specifications vs. what Rich Solar advertises, I am going to pursue other alternatives.



Thanks again!

 

[downhiller]

The only caution one needs is to understand the so called safe voltages are those below aobut 45V. Think old telephone systems with 48 VDC huge batteries.

Can you explain more what you meant by this? Thank you.

 

[foggysail]

Can you explain more what you meant by this? Thank you.

Sure---- OSHA considers all DC voltages above 50 hazardous

 

[12VoltInstalls]

Given that Rich solar never replied to my inquiry about whether their 33 cell panels have diodes, and given the uncertainty respecting the actual specifications vs. what Rich Solar advertises, I am going to pursue other alternatives.

I have 4 Rich 100W poly panels that perform very well. I’m not going to pull one off to pop open the diode/junction box but I’d be shocked if they didn’t have diodes. They play well with 4 WindyNation monocrystaline 100W panels

 

[12VoltInstalls]

Can you explain more what you meant by this? Thank you.

The “let-go” voltage of DC maxes out a bit over 50V by ‘definition.’ 40VDC can still kill you but not likely you’ll hold on long enough to do that, though it can burn you.
50VDC isn’t likely to immediately kill you either but it may and is probable it may immobilize you long enough to inflict severe injury- or kill you. 90VDC can shut vital systems down or un-time your heartbeat and may kill you dead on the spot or wack out your body that you collapse dead later or die that night in your sleep.

Is that true all the time? No. Maybe not even close- but the probabilities are a risk factor too great to ignore or take lightly. I can’t remember exactly now (not a joke, it’s just long ago) but 24VDC tingled me once. It was more than a tingle really but I suddenly became more respectful of DC is what I remember.

 

[foggysail]

Is that true all the time? No. Maybe not even close- but the probabilities are a risk factor too great to ignore or take lightly. I can’t remember exactly now (not a joke, it’s just long ago) but 24VDC tingled me once. It was more than a tingle really but I suddenly became more respectful of DC is what I remember.

Yes! I believe I had a Chevy back when I was younger. I could not drive it with my arm resting on the open door window space while my other steered the vehicle. It seemed that somehow my hand on the wheel also touched the horn ring. It tingled enough to make me keep my hand/arm it away. The car only had a 12V battery for electrical power but instead of closing the horn circuit by making the horn ring DC common, they made it +12V and energized the horn when the ring was pushed.

 

[featherlite]

12Volt,
Thanks for the timely reminder and good explanation!