Mismatched Solar Panel Array

I am buying a 2005 dodge sprinter with a unknown 200w solar panel fixed to the roof.

I am planning and have purchased a lot of equipment to 'upgrade' the solar system to the 12V system. I have purchased 2-100amp LiTime Lithium batteries, 2000w Renogy pure sine inverter, Renogy 40A MPPT charge controller, Renogy 20a DC to DC charger, Renogy Battery Monitor, 20A Battery Charger, plus 12v components for circuits.

I have purchased 2 - 100w renogy solar panels (24.3VOC, 5.21 Amps Open current).
I am thinking/(hoping???) the 200W solar panel fixed to the roof will be around the same as other 200W panels with specs of (23VOC, 11.05 amps open current)

My question is to maximize my solar input efficiency and safety to my 40amp MPPT Renogy Charge Controller.

Can I connect the 2 - 100W panels in parallel, then connect the 200W panel in series?

my calculations would give me 47.3 VOC and 10.42 Amp open current.

Would anyone be able to provide some technical advise?
I have also purchased 3 - 125W panels from Costco that i am planning on returning. They show on the box a 7.3amp rating. But, i am not sure how the math would work out to be efficient.

thanks a lot in advance

true north said:

my calculations would give me 47.3 VOC and 10.42 Amp open current.

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If your assumptions are correct, the above is correct.

You would have about 47.3Voc * 0.8Vmp/Voc * 10.42A * 0.95Imp/Isc = 37.84Vmp * 9.9Imp = 375W out of 400W rated.

Thanks for the reply.
I have seen a lot of solar panel arrays connected in series then parallel. But, not a lot of parallel then series.
Is there considerations to account for when doing a parallel then series circuit?

Should I branch the single 200W panel series circuit off of the Positive or Negative from the 2-100W parallel circuit?

true north said:

Thanks for the reply.
I have seen a lot of solar panel arrays connected in series then parallel. But, not a lot of parallel then series.

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It is definitely unusual to do it this way.

But if the 200W panel is indeed same voltage just twice the current it should be roughly equivalent to two 100W panels in paralell.

true north said:

Is there considerations to account for when doing a parallel then series circuit?

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Its always good to fuse/have diodes. You may wish to research and do that for the peace of mind, but I read in general fusing paralell panels is not necessary when paralelling two of the same panels/strings, because even if one panel develops a short the other dumping its full current through the short will not cause a fire, because the max current rating will not be exceeded. I still have fuses on my paralell strings (even just 2).

true north said:

Should I branch the single 200W panel series circuit off of the Positive or Negative from the 2-100W parallel circuit?

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It shouldn't matter.

It is best if you can find the datasheet or at least specs for the 200W panel. Failing that you can always measure.

Luk88 said:

It is definitely unusual to do it this way.

But if the 200W panel is indeed same voltage just twice the current it should be roughly equivalent to two 100W panels in paralell.

Its always good to fuse/have diodes. You may wish to research and do that for the peace of mind, but I read in general fusing paralell panels is not necessary when paralelling two of the same panels/strings, because even if one panel develops a short the other dumping its full current through the short will not cause a fire, because the max current rating will not be exceeded. I still have fuses on my paralell strings (even just 2).

It shouldn't matter.

It is best if you can find the datasheet or at least specs for the 200W panel. Failing that you can always measure.

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What would be considered too excessive in terms of different voltage (VOC) when combining circuits in series?
I am aware that the voltage doubles in series, but would a certain voltage difference be dangerous?

And when combining in parallel, is the short circuit open current used or the operating current used for calculation?

Many thanks

true north said:

What would be considered too excessive in terms of different voltage (VOC) when combining circuits in series?

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Someone else may need to re-confirm this just in case, but I don't think there is any problem with voltage (VOC as well as VmaxP) difference in a series connection(as long as you don't exceed max system voltage). Likewise there is no problem mismatching on current in a parallel connection in normal operation. In fact we have this all the time with shading. This is what blocking/bypass diodes have been invented for.

The key is to match on current in series strings and on voltage in parallel strings. If you're looking for maximum efficiency it may not even be as simple as comparing VOC and short circuit current, but the entire I/V curve should be compared(usually in a datasheet). If you use same technology panels they will have same shape I/V curves just scaled up or down so VOC and I-short-circuit is probably good enough.

true north said:

I am aware that the voltage doubles in series, but would a certain voltage difference be dangerous?

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As long as you don't exceed max voltage of your mppt nor max system voltage (usually printed on panels) it should be fine.

true north said:

And when combining in parallel, is the short circuit open current used or the operating current used for calculation?

Many thanks,

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I'd look more towards maximum power current with same tech panels. Or even better the I/V curve.