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 > Series-parallel configurations for solar panels

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Cptnvideo

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Posted: 06/13/22 08:45pm Link  |  Quote  |  Print  |  Notify Moderator

We have 6 200 watt panels on the roof of our 5th wheel. Considering adding 1 or 2 more panels for those cloudy days.
Our 6 panels are arranged as 3 in series, 2 strings parallel. Our Victron MPPT controller is the 150/100. The manual says 100 amps and 150 volts are max and mentions a "nominal" of 1450 watts. Our solar system company says we can go to 8 panels in a 4 series, 2 parallel configuration. But I'm a little leery.
We could add a 100 watt panel to each string, making 1400 watts total. But do the 2 parallel sets have to be of equal wattage? Could I just add one 200 watt panel to one of the series strings? I realize that would create unequal voltages, but MPPT controllers convert the voltage anyway. Think about what happens when one panel gets shaded.
Thoughts and opinions?


Bill & Linda
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Posted: 06/13/22 09:39pm Link  |  Quote  |  Print  |  Notify Moderator

If I understand you correctly, If you were to add one more 200w panel to say one of the existing series strings, assuming that the two paralleled strings outputs are tied together before entering the controller, the string with the now higher voltage would simply default to (or equalize with…) the voltage of the opposite string, thus no net increase in voltage…

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ktmrfs

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Posted: 06/13/22 09:54pm Link  |  Quote  |  Print  |  Notify Moderator

Based on my experience I'll make the following comments.
1) parallel panels or strings should all be the same or close to the same string voltage, each panel or string can have different current rating and the MPPT controller will accomidate.
2) All panels in a series string should have the same or similar current rating (power). The string will be limited to the lowest current output of the panel in the string.

so based on your setup adding a 100W panel to a series string is not a good idea your limiting the current from a string, nor is adding a 200W panel to only one string, now you have parallel strings with different total voltage which the controller will likely have a fit with.

Now what to do? well you could add a couple or maybe 3 200 or 100W panels in series and run them to another MPPT controller and parallel controller output to the battery. check and see if the system allows parallel controllers

this is basically what I have on my trailer. roof has 3 200W panels in parallel to a Mppt controller (Midnite solar) and up to 4 200W portable panels I can use wired to another of the same controller. with the midnite solar system one controller is the master (roof) and the other the slave (portable). Master determines which mode the system should be in, bulk, float etc. and sets the slave to the same setting so both controllers are giving the same charge profile.

Depending on how far my portable run is and how much (or little) shade panels see I wire the portable panels in series or parallel, or a series parallel combo.

Have used this for years and it works great.


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Posted: 06/13/22 10:03pm Link  |  Quote  |  Print  |  Notify Moderator

For maximum results the 100 and 200 panels in series must have the same amp rating ie Imp. For the 2 parallel strings the 2 strings should be same voltage ie Vmp. Best to use the same panels.

MPPT does convert the panel voltage/amps (power) to the battery voltage/amps. The problem with a mismatched parallel pair is he loss of overall power.

Find out how your contoller handles more that 1450W. Mine limits the amps when over panneled. Plus you are not likely to ever reach the maximum watts as a bright clear day with the panels pointed directly at the sun is required. So depending upon the over panel answer add 2x 200W OR a second controller with 400W.


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time2roll

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Posted: 06/13/22 10:06pm Link  |  Quote  |  Print  |  Notify Moderator

Parallel needs to be equal voltage. Series needs to be equal in amps. 4s2p configuration will work fine.


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Posted: 06/13/22 10:20pm Link  |  Quote  |  Print  |  Notify Moderator

A little more techincal: For panels in series with different amp rating the entire string amp rating will be equal to the lowest panel amps and the string voltage will be the total voltage of all of the panels.

For panel strings in parallel the voltage will be the lower of the 2 strings. Adding a single panel to one string will not be useful.

Cptnvideo

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Posted: 06/13/22 11:18pm Link  |  Quote  |  Print  |  Notify Moderator

Excellent answers and I appreciate the feedback.

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