Solar panel series string lengths

[IrishG]

Looking for some advice please on cable lengths. Im worried my distance is too far.

Basically the distance of my panels to the inverters is 38m (125ft). Unfortunately the inverters are west of the string so either the plus or the minus have to be much longer than this again.13m (42ft). Also already on panels is 1.2 long on each panels with is adding a further 28.8m (95ft).

Should I be cutting the mc4's off the panels and putting my own on so they are much shorter? is there any reason I shouldnt do this?
Without cutting the cable on panels the yellow string's total length would be: 80m (262ft) and if I cut them it would be 55m (180ft)
Does it make any difference having the plus of minus as the longer one?

Image has 3 strings in series. the yellow im using in the above example. The are positioned orientated and grouped like to do minimise shading.
Im using 6mm2 (10awg) solar cable. The total voc of string is 450 and the max amps is 15a

thanks in advance for any advice

G

 

[CaliSunHarvester]

I would not cut the wires on the panel. There are voltage drop calculators, have you tried them?

I have an array that is about 380ft round trip frpm inverter to the first panel, I also use 10AWG. 2 strings, each 20 panels @ 21Voc or 17.2Vmpp.
Let me look.. inverter receives 375V right now.
That's 18.75V per panel. It's somewhat overcast. Panels are from 2004.

Panels are rated 123W and right now at noon produce .. about 40W each. Yesterday in sun they put out 85W each.

 

[IrishG]

I would not cut the wires on the panel. There are voltage drop calculators, have you tried them?

I have an array that is about 380ft round trip frpm inverter to the first panel, I also use 10AWG. 2 strings, each 20 panels @ 21Voc or 17.2Vmpp.
Let me look.. inverter receives 375V right now.
That's 18.75V per panel. It's somewhat overcast. Panels are from 2004.

I have tried the voltage drop calculators. They are fine as long as voltage remains high, but Im in ireland and its grey alot so im guessing it would often have fairly low voltage.

For what reason to not cut the long cable on the panels?

 

[CaliSunHarvester]

For what reason to not cut the long cable on the panels

For ME.. It's just a lot of work with the risk of creating a poor connection when I make my own MC4s.

Also, does the voltage really drop with less sun?
To me it seems that voltage remains high but current drops.

 

[SeaGal]

so im guessing it would often have fairly low voltage.

Current will drop a lot, voltage minimally - look at the I-V power curves of PV panels.

IMHO those distances are fine at 400V+. Gains for shortening MC4's are insignificant.

 

[IrishG]

One of the cables plus or minus needs to be longer than the other by about 14m ish. Does it make any difference to voltage drop if plus or minus is the longer. Is it better to have the minus as the longer run for example? I presume it doesnt make a differentce but I just want to double check

 

[SeaGal]

No difference at all overall - same current flowing through one loop of wire.

 

[wpns]

It’s a series circuit, it doesn’t make any difference.

IMHO, the time and expense and risk of failure of trimming the wires back exceeds any possible gain. What if you want or need to add rapid shut down or optimizer boxes in the future, and certain wires are too short?

 

[Zwy]

I have tried the voltage drop calculators. They are fine as long as voltage remains high, but Im in ireland and its grey alot so im guessing it would often have fairly low voltage.

For what reason to not cut the long cable on the panels?

String voltage will remain high, it is current that will drop.

I run 420 feet one way from array to house. The key is high string voltage and less amps will give best efficiency unless the array has shading issues, however, a large array that has partial shading will have multiple strings.

Don't worry about the cables on the panels.

 

[Hogheavenfarm]

I run 300ft round trip at only 80v - I put a meter at the panels and at the inverter and have about a 2v drop with 10g wire, no issues at all.