Wire Sizes

Soulearner

Various calculators on the web for solar wire sizing seem to offer vastly different solutions.

Two of them resolve that panel to controller wires carrying 34 volts @ 11 amps (peak output) over 50' = 8 awg
Another states that the voltage drop is too great for 8 awg, and thus a larger cross-section wire is needed - possibly 6 awg

This is driving me crazy...

Cariboocoot

Re: Wire Sizes

8 AWG is fine for that.

Here is a little trick: drop the Voltage down to the nearest standard nominal and see what the calculator says. If it's less than 3% V-drop, then all is well.

If the calculator merely says "yes/no" don't use it.

gww1

Re: Wire Sizes

Did both caculators give the percent of volt drop? I shot for 3 % or less, however it only hurt the most at full amps a small part of my day. So mid bright day is when your drop hurts the worst. So my opinion is if panels run 80% most times you don't lose much by fudging a little. I tried not to fudge incase I add a bit more solar.
Just my thoughts and I used on line caculators.
gww

vtmaps

Re: Wire Sizes

Soulearner wrote: »

Various calculators on the web for solar wire sizing seem to offer vastly different solutions.

that panel to controller wires carrying 34 volts @ 11 amps (peak output) over 50' = 8 awg

Perhaps it's the 'round trip' issue. Is that 50 ft the one-way or the round-trip distance?

That current and voltage through 100 ft of #8 copper (50 ft one way) will give a voltage drop of 2.1%.

If you told the calculator that the copper distance was 100 ft, and the calculator thought that was the one-way distance, it would give a voltage drop of 4.2% with #8 wire, and would probably recommend #6 wire which would have a voltage drop of 2.6%.

--vtMaps

Soulearner

Re: Wire Sizes

Yes, total distance - array to controller is 50'. 4 100W Renogy panels, 2 sets in series then paralleled to a 24V 10A output to the controller = 240 watts. Which is something else I misunderstand....the wattage sum exceeds the panel rating....?????
This calculator causing my consternation was the outlier among the ones I found online:
Attachment not found.
This calculator confirmed what Cariboocoot stated, and with his and it's in hand I am relieved!
Attachment not found.

off subject: the Renogy instructions do not mention grounding. Is it necessary to ground the array?
Thank you all

vtmaps

Re: Wire Sizes

Soulearner wrote: »

This calculator causing my consternation was the outlier among the ones I found online:

Well, for one thing, you have 40 meters of copper (round trip). That's a lot more than 100 ft. Also, that calculator assumes you are using PWM controllers and "battery voltage" panels. Also, this calculator shows voltage drop in volts... most calculators show voltage drop as a percent.
When I wrote:

That current and voltage through 100 ft of #8 copper (50 ft one way) will give a voltage drop of 2.1%.

I was using the numbers you gave in the OP: 34 volts and 11 amps. I was assuming that was Vmp and Imp and that you had a 374 watt array and were using MPPT controller. With 24 volts and 10 amps through 100 ft of #8 copper (50 ft one way) your voltage drop will be 0.641 volts which is a 2.67% voltage drop.

--vtMaps

Cariboocoot

Re: Wire Sizes

Wattage rating of a panel is Vmp * Imp. This won't be "24 Volts" because a "24 Volt" panel has a Vmp of 35. The Renogy 100 Watt panels for example have a Vmp of 18.9 and Imp of 5.3 = 100 Watts.

It is not actually necessary to ground the array for operational reasons; it is done for safety reasons. Whether you do and how you do it depends on the specific application.

Soulearner

Re: Wire Sizes

Well....alright....
Perhaps I see this from the wrong perspective;
If I series 2 sets of 100 watt panels (4), then parallel the two sets, does it not follow:
37.8 volts per set @ 5.3 amps per set.
Paralleled makes 37.8 * 10.6 = 400.68 watts going to the controller
I feel so ignorant in front of you all right now because I now I'm missing something!

Cariboocoot

Re: Wire Sizes

Soulearner wrote: »

Well....alright....
Perhaps I see this from the wrong perspective;
If I series 2 sets of 100 watt panels (4), then parallel the two sets, does it not follow:
37.8 volts per set @ 5.3 amps per set.
Paralleled makes 37.8 * 10.6 = 400.68 watts going to the controller
I feel so ignorant in front of you all right now because I now I'm missing something!

What is wrong? Four 100 Watt panels = 400 Watts. A single panel is technically 100.17 Watts.
Don't worry about tenths and hundredths; panels vary by that much or more from one to another of 'identical' panels.

Soulearner

Re: Wire Sizes

Whew; THANKS.
Thought my record skipped a groove...

Great, I'll pick up the needed 8 awg and be done with bothering y'all.

niel

Re: Wire Sizes

if you plan on upgrading your pv system anytime down the line it may be smart to put the wire size appropriate for the max you'll be sending through them in the future. this would save you from needing to buy more wire later and have to rewire it.

Soulearner

Re: Wire Sizes

I shall consider it Niel, thank you!