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uwedownunder avatar image
uwedownunder asked

different solar panels to Mppt 100/30

Hi Guys, I need some advice in regards to flexible solar panels connected to Victron

Mppt 100/30:

Situation in the moment: 3x 90 watt flexible solar panels (parallel) already installed by the caravan manufacturer

on the pop top roof, Renogy RNG-90DB-H-N, VOC: 21.1V ; Isc: 5.64A ; Vmp: 16.7V ; Imp: 5.38A

connected to the Mppt 100/30 + Smart shunt to 2 x 100 amp AGM in the moment, later down the track to Lithium.

What I try to do: extend the solar system on the roof by two more flexible solar panels. Unfortunately the Renogy RNG-90DB-H-N is

no longer available and discontinued (information from Renogy). I know it is not perfect to “mix” different solar panels in one string. What I found : 90 Watt flexible solar panels, Voc: 21.4V ; Isc: 5.5A ; Vmp: 17.6V ; Imp: 5.1A OR 100Watt flexible solar panels, Voc: 21.6V ; Isc: 6.0A ; Vmp: 17.8A ; Imp: 5.6A

What I try to achieve: Extend the solar system by two more panels on the roof and install 2x 150 Amp Lithium. Not perfect is also, I have to use the existing cable from the roof to the Mppt. The

existing cable size should not be a problem.

Any feed back in regards to the flexible solar panels would really appreciate.

Thanks

Solar Panel
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3 Answers
Alexandra avatar image
Alexandra answered ·

@uwedownunder

I can say from experience it works mixing panels (i am not using flexible but sure the principle is the same.). Had the same issue, went back for more of the same but cannot get them. the voltages of the different panels are so similar it wont really matter in the working conditions.

Just make sure you dont go over the 100V hard limit for input voltage, which I think at 5 panels over 21v each you will. And they produce higher voltages the colder they are. So you may still have to split the array (more wiring) But then if you did that you would need two equal strings of 3 panels. You would need more anyway since you are increasing your battery capacity.


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kevgermany avatar image kevgermany ♦♦ commented ·
Or a second MPPT. Like you say, voltage probably over the limit. And a second solves this, any concerns about mismatch as well as allowing more options for the extra panels.
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gadroberts9 avatar image gadroberts9 commented ·

wedownunder, I’m glad to hear mixing panels works. I too had the same problem purchased 2-190 watt panels and 5 months later wanted to buy 2 more much to my dismay they could never get more in stock. After waiting 2 months I found 200 watt panels that were almost identical in every manner (even size and electrical characteristics) and feel it won’t be a problem since they are so close. But I’m a newbie but I’m giving it a try. I’ll close to the limits after adding the 3 n 4 panels I’ll most likely add a second charge controller so that I don’t go over. I would like to have a 20% safety factor. Can’t afford to smoke my Victron equipment.

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uwedownunder avatar image
uwedownunder answered ·

Hi John, thanks so much for your answer to my question !!! Sometimes miracles are happened, yesterday I found a place where I can get the same new Renogy 90 watt panels like I already have on my pop top roof. Means know I have 5 identical panels. For the future it is maybe good to know: What are the imported parameters if someone have to connect / mix " different" solar panels (parallel in one string connected to one Mppt) How close have to be Vmp / Imp / Voc / Isc from one panel to the other ?

In regards to your advice : " hard look the existing wiring" 5 Renogy panels a 90 watt: Imp 5.38 Amp

5 x 5.38 Amp = 26.9 Amp ( of course in the "perfect world" ) but the panels will never be in the perfect position, installed flat on the caravan roof. The cable to the Victron Mppt 100/30 is 6 B&S that should be big enough for 26.9 Amp and even less in the "real world".

I would really appreciate to hear from you again !!

Thanks Frank

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JohnC avatar image JohnC ♦ commented ·
@uwedownunder

It's really hard to be definitive with this. Cells may be of different types and have different characteristics wrt temp, light intensity, etc. And who knows how good their published specs are, or how much variance there is in manufacturing tolerances?

Panels like yours are usually called '12V', and designed to cover use of cheapo pwm chargers, which can slug dose panel power anywhere from Voc to a little above Vbat. Mppts do a better job of course, and will seek out the optimum Vmp. In cases of serious mismatch there may even be two Vmp peaks in the curve. But will still be better than pwm.

In really poor light like sunup/sundown panel specs drop. Victron mppts need 5V between Vbat and Voc, then once started 1V to the Vmp. You may come across this, and the only solution is to series the panels in pairs. With 5x panels you can't do that, but the minor losses may be compensated by better selective shade tolerance. So it's all about tradeoffs. But enough of that.

Your wiring gauge is plenty, and it's great you've found matching panels. Good luck with it all.


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t1-terry avatar image
t1-terry answered ·

If you squeeze one more panel on the roof you could connect them in 2 string of 3 panels in series. The advantage is the higher input voltage will start the MPPT controller up earlier and keep it running into the late afternoon .... and .... greatly improve any cloudy/wet weather solar input.

The two series strings can be connected in parallel on the roof so the one set of cables can till be used from the roof to the solar controller. Because you have good cabling there is no issue here, but if you had the standard poor caravan cabling that comes from a factory install, 6mm auto cable or 4.34mm sq conductor, the increased voltage and reduced amps will improve the loss issues between the panels and the controller the under size cable presents.

However, there is another requirement, you need to add blocking diodes where the positives from the series strings join the cable running down to the controller from the roof. This is to stop current running back into either string if a panel in one string is in shade .... without the blocking diode, the current from the string with all the panels in the sun will flow into the string with the shaded panel and not to the MPPT controller. Not only that, it will turn the solar panels in the string with the shaded panel into heater elements because current is being forced back through the panels rather than flowing out of the panels.

The diode in the panel junction box is not a blocking diode, it is a bypass diode to prevent current being forced through a shaded panel. The bypass diode will not protect the panels in a series string from back current flow if a panel in the string is shaded.


Sorry about the lomg post


T1 Terry

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