Adding second solar array in parallel doesn’t double output but stays same

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surfamj asked Apr 6, '21

Adding second solar array in parallel doesn’t double output but stays same

I added a duplicate array of 4 x 200 watt panels in parallel to my Victron 100/30 controller. My first array is wired in series and would produce about 420 watts on a sunny day. I figured I would add another 4 identical panels in series as a second array and then wire the two arrays in parallel. I assumed I would double my output but it stays the same. I can disconnect either array and get the same result. Am I doing something wrong or is this normal? I know the voltage and amperage are under the 100 volts and 30 amps of the controller.

Solar Panel

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wkirby answered · Apr 06, 2021 at 08:42 PM

You did not say what your battery Voltage is, I'll presume that it is 12V.

Your charge controller is a 100/30. That means that your PV array must not exceed 100V. I think you have understood that part already.
The 30 means that the maximum output charging current to the battery is 30A. The charge controller limits this it's self.

So, your battery Voltage increases as it charges it will go to around 14.2 - 14.8V depending upon your battery chemistry. Let's take 14V to make the maths easier.
To get the charge power you multiply the battery Voltage by the current. 14V x 30A = 420W.
This is the 420W that you have observed, adding more PV will not result in any more production. In fact your first array is a 800W array, so it was only partially utilised on a sunny day.
If you have added another 800W, then you'll only really benefit on cloudy days where you could still see the 420W in cloudy weather.

So the bottom line is that your charge controller is undersized for your first array.
You would need a 150/60 just for the first800W array on its own. 14V x 60A = 840W
Then you'd need another 150/60 charge controller for the second identical array.

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surfamj commented · Apr 06, 2021 at 08:53 PM

Ahhh, thanks for that explanation. It really helps a lot! If all the panels are identical then does it make any sense to have a larger controller that can handle both arrays? Or is it more efficient to have 1 controller for each array?

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wkirby ♦♦ surfamj commented · Apr 06, 2021 at 09:07 PM

If the arrays point in the same direction and don't suffer any shading between them then it would be OK to wire both arrays into one controller.
However, the largest capacity Victron controller available is 100A which is 1400W. Both of your arrays add up to 1600W (114A), so you would lose 14% of your array's maximum capacity. How often your array actually gets to reach full capacity depends upon your location and conditions, so you'd have to figure out if this small loss is acceptable to you.
It is not uncommon to have an array slightly over the controller capacity, most of the time the array outputs less than the absolute maximum capacity.

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surfamj wkirby ♦♦ commented · Apr 06, 2021 at 09:16 PM

So if I need another controller anyway. I could get the 150/60 and maybe put 5 panels in series on that and the other 3 in series to the 100/30?

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wkirby ♦♦ surfamj commented · Apr 06, 2021 at 09:24 PM

That could work.
You'd have a 600W array making 420W = 180W wasted in perfect conditions.
The 5 panel array 1000W making 840W = 160W wasted in perfect conditions.

That doesn't seem too bad to me. Also a financially smarter suggestion than I came up with!

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Answer 1 · 2021-04-06T20:30:38Z

michelg answered · Apr 06, 2021 at 08:30 PM

What is the voltage of your battery bank, or batterie ? also, an hello, please and thanks are welcome !

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Answer 2 · 2021-04-06T20:41:14Z

surfamj answered · Apr 06, 2021 at 08:41 PM

I have 4 x 12.8 volt LiFePO4 batteries.

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