Best way to wire these four panels?

[alyaz]

The neighbour just purchased six new panels and we wired them up in two series runs of three.  All working good.

However, his old array was wired really oddly, at least to my thinking.  This old array will be used for a little ‘bunky’ he just built.

Anyway, he has four older panels.
2 are 240 watt.  VOC: 37v  ISC: 8.4 a
2 are 175 watt.  VOC: 44.4v  ISC: 5.4 a

If all four panels can be run to a MPPT controller, is it best to wire one 240 watt panel with a 175 watt panel in series and the other 240 watt panel with the other 175 watt panel in series?  Two series runs?

I suggested a Midnite KID controller.  He has an older 24v Rolls battery bank and not sure what he wants for an inverter yet...

Thanks.

[Vic]

Hi alyz,

The issue with the four older PVs,   is really,   that the 175s must be 72 Cells,   and the 240,  must be 60 Cell PVs.

There is a 20% nominal difference twix those two sets,  just counting the cell number.   Ideally  String Vmps should be within 5% of each other (!0% difference maximum) for parallel configuration,   and Imps,  within 5/10% for series combinations of the two PVs.    Really,   these two sets of PVs are not so compatible,   on the same CC.

BUT,   one 240 and one 175 in each string is the best that you can do,   and the string current will be close to that of the 175s  --  about 5A.    There will be some power loss,   but you could still use all four of these PVs.

Some guessing involved.

Personally usually find that Vmp  and Imp are the most useful values for trying to match PVs.   Voc is most useful for looking at Maximum input voltage to the CC,   at the coldest temps.

Just a drive-by set of opinions.    Good Luck,   Vic

[alyaz]

Thanks Vic.  Appreciate your knowledge.

[RicardoL]

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[ClassicCrazy]

Ricardo - you really need to do a survey of what your loads are . Then the first thing to do is get those as efficient as possible. Then you need to crunch numbers on cost of electricity vs how long it would take to pay off the solar.
If you are doing grid tie there is less cost to the system. If you want to be off grid and have batteries then it will cost you quite a bit more because batteries are expensive .

Larry

[Westbranch]

As well , if you have problems with grid stability, that is another factor to consider, SUSTAINABLE power

[RicardoL]

Thank you, Guys.