String re-config due to colder days?

[LydMekk]

Got my strings in series, 9xLongi 72cells single sided 540w panels, only one string for each inverter (3-phase).

Voc STC 49,50 - NOCT 46,54
Short Circuit Current lsc/A is STC 13,85 - NOCT 11,20
Current at max power Imp/A is STC 12,97 - NOCT 10,43

During summer I see max. 405V. Growatt SPF 5000 ES got a 450Voc max, 430 max useable.
Now in November it has gotten up to 425V. *Tiny bit sweating here now* ... :D

Still around 23C temps during daytime in the shade, nights atm. around 14-15C.
We CAN though have a few days during winter with down to 3-4C degrees in the morning only, back up to 15-25 during early afternoon again - but never any lower (9 years in same area).
No snow. Southern Spain - Andalucia. Solar irradiance locally is 577 max at 13:00 for tomorrow 05.11 f.ex.

EDIT to clarify: Should I connect the last panel in each string to parallell so the total string config is 8 in series+connect the last panel (no. 9) by swapping + and - on it?

I know this lowers the voltage to 360-373 acc. to my numbers above,
but will it also lower the combined strings output in watts if I do this?

Or will I see approx. the same possible max. output as now? 4860w?

 

[timselectric]

Just remove the 9th panel from each string.
Reverse polarity Just turns it into a huge resistance for the other 8.

 

[LydMekk]

Hm. According to Ohms law R=V/A, one panel has 3,57 Ohm STC and 4,15 Ohm NOCT.
So, today the whole string has 445V STC and 32,13 Ohm for example.
As each panel has 3,57 Ohm natural resistance (remember only diodes in these) I can't see how inverting the polarity of one panel should increase the resistance heavily. The panel still has the same internal R.
I assume the polarity of one panel should not affect the total Ohms - shoot me down If I am wrong ^^

Or are there a formula I am missing?

 

[timselectric]

Hm. According to Ohms law R=V/A, one panel has 3,57 Ohm STC and 4,15 Ohm NOCT.
So, today the whole string has 445V STC and 32,13 Ohm for example.
As each panel has 3,57 Ohm natural resistance (remember only diodes in these) I can't see how inverting the polarity of one panel should increase the resistance heavily. The panel still has the same internal R.
I assume the polarity of one panel should not affect the total Ohms - shoot me down If I am wrong ^^

Or are there a formula I am missing?

Pushing the power from the other 8 panels. Backwards through the 9th panel is going to turn it into a heater, in my opinion.
The bypass diodes will actually work as blocking diodes with polarity reversed. Which means that the power from the rest of the string will be forced through the actual cells in reverse of design.

 

[LydMekk]

Hey Timmeh! I hate it when you are right...

It runs as I described it above but it lowers the voltage by 90V instead of 45 and generally generate ca. 20% less than the other two areas.
Going to disconnect the last of the 9 series panels for now in winter.

As I have 10 available for each inverter group I'm thinking of going with 2 strings of 5 panels in series, aka 5S2P.
Should amount to 250V in total on each inverter and 22A instead of around 400+ and 11A.
Sounds good?

I need to upgrade the FW on the 5000ESs first to raise them from the limit today 18A to 22A.
I run the version 5 atm. and that only support 18A.

Did you do the same FW upgrade yourself? Is the version 6 the last published firmware from Growatt on the 5000ESs?

 

[timselectric]

As I have 10 available for each inverter group I'm thinking of going with 2 strings of 5 panels in series, aka 5S2P.
Should amount to 250V in total on each inverter and 22A instead of around 400+ and 11A.
Sounds good?

Personal, I prefer the higher voltage for efficiency.
But, that could work well.

I need to upgrade the FW on the 5000ESs first to raise them from the limit today 18A to 22A.
I run the version 5 atm. and that only support 18A.

Did you do the same FW upgrade yourself? Is the version 6 the last published firmware from Growatt on the 5000ESs?

I haven't done any updates.
And won't, unless I have a problem.
If it ain't broke, I don't want to fix (break) it.