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diy solar

Tell me I’m not wrong

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Green Garden

New Member
Joined
Sep 22, 2025
Messages
13
Location
Kentucky
Hi,
I was sizing wires for the arrays and to achieve a 2% (mathematically) voltage loss was going to require 6 awg wire (2500w with low voltage of around 90). Well my engineer mind kicked in and said this is utterly ridiculous. It’s not possible for me to have lowest voltage and highest current together!!!! That’s like being hot in the winter. So I did all the math for my location and if I use 12awg on all my arrays I end up with a real world site conditions of the following.

2C7D6582-1C4A-4609-8B39-DF89F02279E6.png

As you can see my wiring losses are tiny. These are showing an entire month by hour for a year. I have all 8766 hours if you want it. While looking into chart make sure you pay attention to the units. I couldn’t keep them consistent and still be able to show the losses they totally disappear.

Take June for instance we made just over 2mwh and had line losses of 53kwh this is 2.65% voltage loss this is on the absolute worst month of the year. I would not feel stupid if I use six gauge wire. 🤭

I strongly suggest everyone analyze their own system for their own location with hourly calculations for each voltage (power) loss as I have. You might be really surprised what you learn. I’ve always been a big fan of do your own research and make sure it applies to what you want what you need and what you have don’t ever listen to what someone else has done. Please don’t listen to what I’ve done please do it for yourself.!

Here is everything in consistent units.

1758592652570.png


Month​
PV Generation (kWh)​
Load (kWh)​
Battery Charge/Discharge (kWh)​
Energy Delivered to Load (kWh)​
Clipped PV (kWh)​
Wire Loss (kWh)​
Inverter Loss (kWh)​
Jan
923
1,503
687
1,441
12
23
39

Feb
1,098
1,331
672
1,274
15
27
46

Mar
1,574
1,525
722
1,466
24
37
54

Apr
1,812
1,471
653
1,416
41
45
63

May
2,019
1,503
688
1,448
58
51
72

Jun
2,091
1,471
652
1,417
66
53
74

Jul
2,049
1,525
720
1,470
61
52
73

Aug
1,900
1,503
689
1,444
48
49
71

Sep
1,552
1,471
654
1,416
29
40
61

Oct
1,310
1,525
721
1,463
20
34
55

Nov
1,041
1,471
653
1,419
13
28
47

Dec
876
1,503
687
1,442
10
22
38

Total
18,245
17,801
8,498
17,616
397
461
663
 
Last edited:
Green Garden said:
Hi,
I was sizing wires for the arrays and to achieve a 2% (mathematically) voltage loss was going to require 6 awg wire (2500w with low voltage of around 90). Well my engineer mind kicked in and said this is utterly ridiculous. It’s not possible for me to have lowest voltage and highest current together!!!! That’s like being hot in the winter. So I did all the math for my location and if I use 12awg on all my arrays I end up with a real world site conditions of the following.

View attachment 332212
As you can see my wiring losses are tiny. These are showing an entire month by hour for a year. I have all 8766 hours if you want it. While looking into chart make sure you pay attention to the units. I couldn’t keep them consistent and still be able to show the losses they totally disappear.

I strongly suggest everyone analyze their own system for their own location with hourly calculations for each voltage (power) loss as I have. You might be really surprised what you learn. I’ve always been a big fan of do your own research and make sure it applies to what you want what you need and what you have don’t ever listen to what someone else has done. Please don’t listen to what I’ve done please do it for yourself.!
Click to expand...
Personally I'm not worried about line losses for pv when im running higher currents on my 250/100, 5s3p or 5s4p on 10AWG. It is what it is and I don't feel like ponying up for 8AWG.
 
zanydroid said:
Engineering + 90v system is dubious if the goal was to minimize losses

2500/90 (I assume these are nameplate values) suggests an Impp of 27, which requires #8 minimum anyway after factoring in 1.56 derate
Click to expand...
yes vmp is 18.2 5s4p configuration to match maximum controller input of 160x0.8=128v. VOC puts me about 118 but the example showed using short circuit current with average voltage not maximum voltage with maximum current. Which if we think about it these (low voltage and high current) will never occur at the same time in nature.
 
timselectric said:
Voltage drop losses aren't that important for PV. The MPPT gets whatever it can, one way or another.
Click to expand...
Glad to hear this. Because every place I looked it said I wanted less than 2% voltage drop. As I pointed out the way they have you calculate it you way way way oversize your wiring system like the previous guy that said I’m needed minimum 8AWG wire. That’s sizing based on voltage drop. That would meet the 2% or maybe the 3% I don’t know what he used I know historically it’s 2% on solar and 3% on electrical in general. However looking at the real world losses those calculations just are not right you’re wasting your money calculating wire size like that. The code says minimum 12 AWG. You have a breaker in the system that’s sized for 12 AWG wire so that you don’t burn it in half what you calculate is for voltage drop. That’s not code.
 
Green Garden said:
Glad to hear this. Because every place I looked it said I wanted less than 2% voltage drop. As I pointed out the way they have you calculate it you way way way oversize your wiring system like the previous guy that said I’m needed minimum 8AWG wire. That’s sizing based on voltage drop. That would meet the 2% or maybe the 3% I don’t know what he used I know historically it’s 2% on solar and 3% on electrical in general. However looking at the real world losses those calculations just are not right you’re wasting your money calculating wire size like that. The code says minimum 12 AWG. You have a breaker in the system that’s sized for 12 AWG wire so that you don’t burn it in half what you calculate is for voltage drop. That’s not code.
Click to expand...
When you calculate the voltage drop in any other situation, it is very important.
The difference with PV is that the source (sunlight) is variable and the load (MPPT) is constantly adjusting to the variables. There's no system design voltage that must be maintained.
 
timselectric said:
When you calculate the voltage drop in any other situation, it is very important.
The difference with PV is that the source (sunlight) is variable and the load (MPPT) is constantly adjusting to the variables. There's no system design voltage that must be maintained.
Click to expand...
Thanks! I was talking through grounding plans with my dad (electrician turn electrical engineer) and he explained why I should do it the way I said I planned to. I appreciate the whys!!!!
 
Green Garden said:
Thanks! I was talking through grounding plans with my dad (electrician turn electrical engineer) and he explained why I should do it the way I said I planned to. I appreciate the whys!!!!
Click to expand...
As far as grounding, you don't calculate voltage drop.
But if you increase the current carrying conductors for any code requirement, you also have to increase the EGC by the same percentage.
 
Green Garden said:
yes vmp is 18.2 5s4p configuration to match maximum controller input of 160x0.8=128v. VOC puts me about 118 but the example showed using short circuit current with average voltage not maximum voltage with maximum current. Which if we think about it these (low voltage and high current) will never occur at the same time in nature.
Click to expand...
Have you considered a charge controller with a higher voc limit so you could do 10s2p? Or if you get one with a 500v limit and do 18s with a couple spares.
 
Green Garden said:
you can’t put PV wire in a conduit.
Click to expand...

yes you can. NEC says so
  • NEC 690.31(C)(2) (2023):

    Single-conductor PV wire shall be permitted in cable trays, in raceways, or as exposed, outdoor cables.
    Click to expand...
  • NEC 310.10(C):

    Conductors rated for wet locations (which PV wire is) are permitted in raceways underground or aboveground.
    Click to expand...
  • NEC 300.17 / Chapter 9 Tables:

    Conduit fill and bending radius rules apply if you put PV wire inside conduit.
    Click to expand...
 
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