Mixing panels?

[Bossrox]

I got a question from a member in my solar forum I couldn't answer concisely.

I have mixed panels in my system varying from 310 to 330 watts but the voc on all of them are nearly the same & have no issues but for a theoretically scenerio lets say I have a series string of 3 panels @40v voc each totaling 120v. Then I have another string of 3 of 45v voc each for 135v & hook those 2 strings in parallel.

In my thinking, it's just like 2 batteries, The stronger feeds predominately until the current draw exceeds the stronger then the weaker then adds to it as needed. Is that the way it works or something else?

Is there a limit of difference between combining different voc's & what would be the consequences?

I know some of you would say put widely different voc's on separate chargers but what if you couldn't?

 

[sunshine_eggo]

I got a question from a member in my solar forum I couldn't answer concisely.

I have mixed panels in my system varying from 310 to 330 watts but the voc on all of them are nearly the same & have no issues but for a theoretically scenerio lets say I have a series string of 3 panels @40v voc each totaling 120v. Then I have another string of 3 of 45v voc each for 135v & hook those 2 strings in parallel.

In my thinking, it's just like 2 batteries, The stronger feeds predominately until the current draw exceeds the stronger then the weaker then adds to it as needed. Is that the way it works or something else?

No. MPPTs do a sweep. It will realize there is more power near the Vmp of the 40V panel string. You'll lose the ~10% from the whole array.

Is there a limit of difference between combining different voc's & what would be the consequences?

If the Vmp of the higher voltage string is higher than the Voc of the lower voltage string, high voltage string will short through the low voltage.

I know some of you would say put widely different voc's on separate chargers but what if you couldn't?

10% difference is probably fine.

An MC4 blocking diode on the lower voltage string can be added to prevent backfeeding.

 

[Bossrox]

No. MPPTs do a sweep. It will realize there is more power near the Vmp of the 40V panel string. You'll lose the ~10% from the whole array.



If the Vmp of the higher voltage string is higher than the Voc of the lower voltage string, high voltage string will short through the low voltage.



10% difference is probably fine.

An MC4 blocking diode on the lower voltage string can be added to prevent backfeeding.

That's what I was looking for, makes sense.