Unbalanced PV in series

[RoySalisbury]

In general I know that you should wire panels so that they balance out voltage. However, I recently lost a single panel in an array of 12.

What would be the result of wiring them up into two strings .. one with 5 panels and one with 6. Right now I have had to go down to 10 panels, and would like to get the other into the mix instead of sitting there as a "spare".

The specs for the panels are as follows:

Axitec AC-330P/72S (12)

Nominal Output (Pmpp):	330 Wp
Nominal Voltage (Umpp):	37.70 Volts
Nominal Current (Impp):	8.76 Amps
Short Circuit Current (Isc):	9.27 Amps
Open Circuit Voltage (Uoc):	45.83 Volts
Module Conversion Efficiency:	17.01%
Voltage Uoc:	-0.30%/K
Current Isc:	0.04%/K
Output Pmpp:	-0.42%/K

Thanks

 

[sunshine_eggo]

You've already demonstrated 11S isn't an option and even 10S is marginal.

5S2P is your only option.

5S in parallel with 6S:

You'll get:
1) absolutely nothing as the 6S short circuits into the lower voltage 5S string
2) Get nothing from the 5S, but get 6S
3) get nothing out of the 6th panel in the 6S string

5S2P and be done with it, or replace the 12th panel with something comparable.

 

[RoySalisbury]

Thinking about this more, it seems that "in theory' this would be the same as 2 parallel strings of 6 panels, but ONE of the panels in ONE of the string being 100% shaded.

So perhaps that might be the better question... what is the result of a single shaded panel?

 

[zanydroid]

If the MPPT works correctly then the selected operating voltage will activate all bypass diodes on the shaded panel.

 

[RoySalisbury]

5S2P and be done with it, or replace the 12th panel with something comparable.

Unfortunately, finding a suitable replacement is MUCH harder than you would think. These things go out of stock quickly and become discontinued. Might find one with similar specs, but the size (LxW) is so far out that it wont fit in the array.

I have the same issue with another array that one of the panels got cracked in shipping and they no longer have them in stock.

 

[zanydroid]

If you go series you just need to balance current (or go above rest of string while keeping Isc acceptable). Voltage is only constrained by Voc limit of MPPT.

If you go parallel you just need to balance voltage (again while keeping Isc acceptable).

If you don’t balance voltage you can game out what happens if the MPPT activates either 1 or 2 out of 3 bypass diodes on the higher voltage string, (of course with the caveat that this puts that bypass diodes at higher risk of failure and may void warranty). Note there are several combinations of activation since activating one on different voltage panels will have different voltage drop, I think there are 5 combinations.

1low
1high
1low1high
2low
2high

You can also consider using optimizers to balance either voltage or current with unmatched strings.

 

[zanydroid]

Another option: buy a used microinverter and AC couple that one spare panel into your system.

 

[RoySalisbury]

You can also consider using optimizers to balance either voltage or current with unmatched strings.

I've never looked at some type of optimizer. And not sure how a microinverter would work.

 

[zanydroid]

I've never looked at some type of optimizer. And not sure how a microinverter would work.

Tigo optimizers can drop voltage/increase current to match. They have several white papers that are written for easy consumption. They can boost current/drop voltage by about 30%. You would need one per panel IIRC.

Microinverter — it’s an inverter mounted under the solar panel, DC in on one side AC out on the other side. You then tie the AC into your electrical system. They are a good solution for very small arrays. Microinverters are predominantly grid tie.

I did a quick search and 4 TS4-A-O costs the same as one IQ7. Since you need 11 optimizers for your config (IIRC) the microinverter is cheaper. And I believe microinverters have a bigger install base in the US compared to TIGO

 

[SamDeleted]

5 and 5 , or 6 and 6


Get another panel yours are a common size / voltage, should be easy to replace

 

[AntronX]

Unfortunately, finding a suitable replacement is MUCH harder than you would think.

Took me 5 minutes: https://www.santansolar.com/product/used-boviet-370w-solar-panel/