Wiring size issues.

[diegodog]

Hello Again! I'm in need of more help from the crew.

I've been watching videos and reading in the attempts to select the proper wire size to connect my panels together. After going through the initial noob panic attack as I did my first calculations in parallel, freaking out as the wire thickness blew up to unthinkable thicknesses, I luckily read on and am wiring things up in series. Getting past this point and having my panel specs I started using the online calculators and my results are varying wildly.

Going against some of the advice here (from people way more knowledgeable than me) I am going to go with 3 SunnyBoy 6k inverters due to them not needing the optimizers. With 60 panels the price of the SolarEdge + the optimizers got out of budget for me (my panels will be in an open field). SB has me running 2 strings of 10 panels to each of the 3 inverters for a total of 60 panels. I'm assuming that each of my strings will be producing at maximum 451 volts and 9A. My first concern is what I hope to my dumb question for the day is if both strings are producing 450 volts that is 900 total volts going into the inverter. I hope that does not violate the 600 volt rule and that the SB takes care of things in there. I also have read there needs to be some extra wiggle room in the calculations as well.

My furthest panel will be around 200 ft from the inverter.

In my results I've gotten anything from 14awg to 0awg. I'm going to run way thinker wire than I need due to the fact I'm a rookie and it's nice insurance but the results are so massively different I'm afraid I'm missing something. Can you guys get me back on track?


Panel Specs.
305 Watts
Imp 8.5A
Vmp 36V
Isc 8.8A
Voc 45.1V

DC Electrical Characteristics

STC Power Rating 305W
PTC Power Rating 273.3W 1
STC Power per unit of area 14.5W/ft2 (155.9W/m2)
Peak Efficiency 15.59%
Power Tolerances 0%/+3%
Number of Cells 72
Nominal Voltage not applicable
Imp 8.5A
Vmp 36V
Isc 8.8A
Voc 45.1V
NOCT 46°C
Temp. Coefficient of Isc 0.05%/K
Temp. Coefficient of Power -0.43%/K
Temp. Coefficient of Voltage -0.144V/K
Series Fuse Rating 15A
Maximum System Voltage 1000V

Mechanical Characteristics

Type Polycrystalline Silicon
Output Terminal Type Multicontact Connector Type 4
Output Cable Wire Gauge 12 AWG
Output Cable Wire Type PV Wire
Output Cable Wire Length 47.2in (1,200mm)
Frame Color Clear
Length 77.2in (1,960mm)
Width 39.3in (998mm)
Depth 2in (50mm)
Weight 51.1lb (23.2kg)
Installation Method Rack-Mounted

Warranty and Certifications

80% Power Output Warranty Period 20yrs
90% Power Output Warranty Period 10yrs
Workmanship Warranty Period 10yrs
UL 1703 Fire Classification Type 1
Compliances UL 1703, IEC 61215, IEC 61730
CSI Listed Yes

[Raj]

360 volts per string at 8.5 amps. 2 strings in parallel, 360 volts at 17 amps. Number 10 AWG would be adequate at less than 1 percent voltage drop. If run to inverter will be carrying amperage of 2 strings then number 8 AWG is about 1 percent voltage drop.

[Mike90250]

Here's a link to a handy spreadsheet, for calculating wire run/size
find the tab for the page for instructions and read to the bottom of it,

Calculator spreadsheet

http://www.solar-guppy.com/download/voltage_drop_calculator.zip

more calculator options

http://www.solarpaneltalk.com/showthread.php?2312-Wiring-interconnect-goodies-amp-volt-drop-loss-calculator

[diegodog]

360 volts per string at 8.5 amps. 2 strings in parallel, 360 volts at 17 amps. Number 10 AWG would be adequate at less than 1 percent voltage drop. If run to inverter will be carrying amperage of 2 strings then number 8 AWG is about 1 percent voltage drop.

Thanks Raj. You blew my mind hooking the strings at the end thus negating the high voltage issue I was not getting. Thanks for that.

[Raj]

Glad to be of help

[diegodog]

Here's a link to a handy spreadsheet, for calculating wire run/size
find the tab for the page for instructions and read to the bottom of it,

Calculator spreadsheet

http://www.solar-guppy.com/download/voltage_drop_calculator.zip

more calculator options

http://www.solarpaneltalk.com/showthread.php?2312-Wiring-interconnect-goodies-amp-volt-drop-loss-calculator

Thanks for the proper spreadsheets! Great resource.

[diegodog]

Here's a link to a handy spreadsheet, for calculating wire run/size
find the tab for the page for instructions and read to the bottom of it,

Calculator spreadsheet

http://www.solar-guppy.com/download/voltage_drop_calculator.zip

more calculator options

http://www.solarpaneltalk.com/showthread.php?2312-Wiring-interconnect-goodies-amp-volt-drop-loss-calculator

Dumb question. In the spreadsheet for "array voltage" would I want to put the (panel volts x number of panels) here which in my case with 36v panels and 10 in each string 360v. Just want to make sure I don't want to use 36. Lower in the spreadsheet it auto fills the field (panel voltage) with the 360v and that seems wrong.

Also thinking abut this wire. Any issues or concerns with this type?

http://www.ebay.com/itm/112057758950?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Thanks

[Mike90250]

Dumb question. In the spreadsheet for "array voltage" would I want to put the (panel volts x number of panels) here which in my case with 36v panels and 10 in each string 360v. Just want to make sure I don't want to use 36. Lower in the spreadsheet it auto fills the field (panel voltage) with the 360v and that seems wrong.

I think that spreadsheet wants the STC number for Vmp and then you tell it how many panels in the string, and each row is an additional string
So yes, 10 panels in a SERIES string, is 360V, which seems a tad on the low side for a string inverter.

Also thinking abut this wire. Any issues or concerns with this type?
http://www.ebay.com/itm/112057758950...%3AMEBIDX%3AIT

If it's not counterfeit it would work. I think that's a higher grade than needed, usually, there is a weatherhead on the roof and once the wires go inside, you don't need the exterior UV weather resistant wire