# Acceptable line loss

idiggplants
Posts:

**27**Registered Users ✭✭
OK, so quick background... I have a 100w renogy panel and a 20a mppt controller. they are charging a battery at my remote pavilion. will be powering a car radio and a handful of led lights, summertime only, for about 4 hours a night. 3 nights a month, or thereabouts. i will also be substituting power with a jump pack on the shady days.

I had planned to put the panel on the roof, which is pretty shaded. see what that got me, and then add a 2nd or 3rd panel.

someone mentioned to me that i might be better off putting the panel(s) 125' away in a sunny field. What is the actual acceptable line los % and end of run voltage? this is a budget build, so i was hoping to use some of the endless 12-2 uf wire that i have lying around. The way i see it, even at 50% loss, id still be getting the same amount of energy as i would on the roof. I know, however, that i cant let the voltage drop too low, or the CC wont be able to use the energy.

im using this calculator, and im unsure of what amperage and voltage to put in for the panels.

I had planned to put the panel on the roof, which is pretty shaded. see what that got me, and then add a 2nd or 3rd panel.

someone mentioned to me that i might be better off putting the panel(s) 125' away in a sunny field. What is the actual acceptable line los % and end of run voltage? this is a budget build, so i was hoping to use some of the endless 12-2 uf wire that i have lying around. The way i see it, even at 50% loss, id still be getting the same amount of energy as i would on the roof. I know, however, that i cant let the voltage drop too low, or the CC wont be able to use the energy.

im using this calculator, and im unsure of what amperage and voltage to put in for the panels.

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## Comments

2,314Registered Users ✭✭✭✭A second problem is the voltage from a single panel (or multiple panels in parallel) may not put out high enough voltage for an mppt type controller, especially when the panel heats up in the sun. IMHO, a pwm type controller would be a better choice for a single nominal 12v panel.

If you have a sunny spot 125' away, and are willing to add a second/third panel, you could wire in series to minimize voltage drop and make better use of the mppt controller. 3 panels in series would be ~54v and 5a. At 125' using 12ga wire would be ~5% voltage drop, which isn't terrible.

Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

27,433Super Moderators adminFor example, if you have a 12 volt battery bank--You need ~15.0 volts minimum for charging (depending on battery type, temperature, etc.). And a minimum of 2 volt drop across the MPPT charge controller (reality, you probably want >10 volt drop--But that is another story).

So, for a typical higher end charge controller, you need ~17 volts minimum at the charge controller... And the maximum recommended input voltage Vmp-array is ~100 VDC (again, depends on local temperatures and specific controller model). But, roughly you are looking at an "allowable" drop of 100-17=83 volts from array to charge controller.

Realistically, there is almost never any reason to design for that high of drop. Typically 1% to 3% drop is a good design range. If you try to go below 1%, you are just throwing lots of money at copper for little gain (1% to 0% loss). 3% drop maximum is a typical number for functional loads without problems (i.e, 120 volt load * 3% = 3.6 volt drop for your AC loads).

Specifically, you have to look at your loads with solar... For example a 12 volt lead acid battery bank runs from ~10.5 volts dead to ~16.0 volts (equalization charge). Say you pick 11.5 volts as your minimum battery voltage (don't want to damage battery)... And you have a 12 volt AC inverter with 10.5 cutoff voltage... That gives you 1.0 allowable drop, but since a typical inverter can draw 2x current (for starting loads), you really only want a maximum voltage drop of 0.5 volts for wiring+breaker+fuses/etc. to load... 0.5 volts / 12 volts = 4% drop...

I recommend that you design two different systems (at least) on paper and see what works best for you... With the standard warning the solar PV panels only generate "useful" power in full sun, ANY SHADE will dramatically reduce output (by 50% to 100% typically). People do argue that parallel vs series connections of panels can reduce shading power reduction--Just try for no-shade between 9am and 3pm at least.

Let us try a couple very quick rule of thumb designs... One with a PWM controller and another with MPPT. Say you have 2x 6 volt @ 200 AH golf cart batteries (very nice for a starter/training/learning system--Decent power and cheap if you make any mistakes and murder the batteries--very common for first time systems).

Rule of thumb charging is 5% minimum (weekend/sunny season systems) and 10% to 13% rate of charge for full time off grid systems. For your needs, 5% minimum rate of charge should work:

Lets pick two configurations. 2x 100 watt panels in parallel for PWM controller and 2x 100 watt panel in series for MPPT controller

Lets say you want a PWM controller and 125 feet of "one way" wire run (for the following voltage drop calculator)...- 200 Watt array * 1/17.5 volts Vmp = 11.4 amps Imp-array
- 17.5 Vmp * 0.03 drop = 0.525 volt drop

Voltage drop calculator for 125 feet one way run:https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.5127&voltage=17.5&phase=dc&noofconductor=1&distance=125&distanceunit=feet&eres=11.4&x=56&y=20

>2 AWG:

Voltage drop:

0.45Voltage drop percentage:

2.57%Voltage at the end:

17.05Now, same thing with MPPT charge controller but two panels in series:

Voltage drop calculator for 125 feet:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=35&phase=dc&noofconductor=1&distance=125&distanceunit=feet&eres=5.7&x=67&y=21

>8 AWGVoltage drop:

0.90Voltage drop percentage:

2.57%Voltage at the end:

34.1And if you allowed >3% drop, you could even use 14 AWG cable:

Voltage drop:

3.60Voltage drop percentage:

10.29%Voltage at the end:

31.4That would cost your ~20 Watts from your array (in full sun/maximum current)--But it would still work fine with MPPT controller and only a little bit less than the 5% rate of charge recommended for 2x golf cart batteries for charging current.

The higher voltage you go on the solar array (with MPPT controllers), the smaller copper wire you need from array to charge controller.

It all depends on how much energy you need (Watts*Hours or Amp*Hours*Volts defines size voltage & AH of battery bank).. And the battery bank plus hours of sun per day define the size of solar array... Then you start picking equipment and configurations that will meet your needs.

The above is not a complete design discussion--But trying to show your options for a 125 foot feed from array to point of use for a smallish 12 volt battery system.

Your thoughts?

-Bill

5,024Solar Expert ✭✭✭✭Use this calculator,it is a bit easier. Be sure to use the 2 way wire length PV > battery > PV.... you can fill in any BLUE value, and it will populate where needed

KID #51B 4s 140W to 24V 900Ah C&D AGM

CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM

Cotek ST1500W 24V Inverter,OmniCharge 3024,

2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem

Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep

West Chilcotin, BC, Canada

914Solar Expert ✭✭✭✭.

125 feet away in a open field could work if you plan to deploy the panels only while you are there. Hopefully you wouldn't have to deal with gusty winds which will require a solid mounting That distance would require a higher voltage series wired array. The higher the better and also some larger gauge wire to limit voltage drop to an acceptable level. This type of setup will definitely require an MPPT controller and up to 6 series wired 12 volt panels, depending of the Voc. limit of the controller.

Figure which controller you will use and the highest voltage allowed then you can figure out how many series wired panels you can use and come up with your voltage and current. Current of a series wired string is the same as a single panel. the voltage is what adds.

2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

914Solar Expert ✭✭✭✭2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

202Solar Expert ✭✭✭27Registered Users ✭✭The big question I have is.. If I run double 12/2 uf wiring, and one 100w panel... Will it put any charge on the battery? Or will I absolutely need 2 100w panels to run the array at 24v?

Also still not sure what volt and amp numbers to put into the calculations.

914Solar Expert ✭✭✭✭The info should be on the back of the panels. If not look up your panels online.

2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

27,433Super Moderators admin2x 12 awg becomes 9 awg. 4x 12 awg becomes 6 awg.

Bill

2,314Registered Users ✭✭✭✭Whether 55ah is enough depends on the car stereo - some take a fair bit of power.

Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer

Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter

27Registered Users ✭✭Maximum Power: 100W

Maximum System Voltage: 600V DC (UL)

Optimum Operating Voltage (Vmp): 18.9V

Open-Circuit Voltage (Voc): 22.5V

Optimum Operating Current (Imp): 5.29A

Short-Circuit Current (Isc): 5.75A

5,024Solar Expert ✭✭✭✭KID #51B 4s 140W to 24V 900Ah C&D AGM

CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM

Cotek ST1500W 24V Inverter,OmniCharge 3024,

2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem

Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep

West Chilcotin, BC, Canada

27Registered Users ✭✭1.2KW off grid system; 2 strings of 2ea 305W 60 cell panels on a redneck ground mount; MNPV3 combiner feeds a MN Classic 150 located 100' away; 12V 460AH FLA battery bank powers a cabin-wide 12V DC system as well as a Cotek 700W PSW inverter; Honda EU2000i and IOTA 55A charger bridge cloudy days and a Champion 3800W generator for short duration, power hungry appliances.

27Registered Users ✭✭> Use Vmp=18.9 and Imp=5.29 in the voltage drop calculator on calculator.net. It is very simple and allows you to put in the number of conductors. At 125' it shows 2.1V drop (11.11%). Using 2 sets of conductors cuts the loss in half.

When you say 2 sets of conductors, does that include the ground wire of the 12-2? So 2 sets of 12-2 gives me a 6%-ish loss aka ~17.76 at the controller? And that should run the controller pretty well yes?

So many thanks folks. I don't want to seem like I'm asking to be spoon fed info I can find on my own via Google... I'm actually at a friend's cabin with very limited service to respond, and I can't get the calculations to go through.

27Registered Users ✭✭1.2KW off grid system; 2 strings of 2ea 305W 60 cell panels on a redneck ground mount; MNPV3 combiner feeds a MN Classic 150 located 100' away; 12V 460AH FLA battery bank powers a cabin-wide 12V DC system as well as a Cotek 700W PSW inverter; Honda EU2000i and IOTA 55A charger bridge cloudy days and a Champion 3800W generator for short duration, power hungry appliances.

5,024Solar Expert ✭✭✭✭KID #51B 4s 140W to 24V 900Ah C&D AGM

CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM

Cotek ST1500W 24V Inverter,OmniCharge 3024,

2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem

Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep

West Chilcotin, BC, Canada

27Registered Users ✭✭so.. i have enough wire to run 2 sets of 12/2 wire. there will have to be a junction box mid way between the panels and the pavilion though, as i have numerous 100' rolls, and a few 30' rolls. not ideal, but i think it will be ok.

looks like that will give me 17.85 volts at the controller. which im thinking will be sufficient?

then ill watch to see if it keeps the battery charged on the majority of days. if for some reason it doesnt, ill add a 2nd panel and that should definitely do the trick.

many thanks again!!!!

27,433Super Moderators adminIf you are happy with the support of your loads (from battery)--It should be perfect with a PWM charge controller.

-Bill

27Registered Users ✭✭4,532Solar Expert ✭✭✭✭For an MPPT type controller, you really need higher voltage. They work best with more 'head room' above the charging voltage. Thought I had said that in a previous thread, but perhaps it wasn't your thread.

27Registered Users ✭✭27,433Super Moderators adminTry it and see how well it works.

Note that charge controllers only output "full array power" to a battery (bank) that is less than ~80% full (this is "bulk" charging)... Batteries that are near full, will naturally have reduced charging current (this is "absorb" charging).

Or, if you have a good size load on the battery (charger should output maximum power when there are heavy/steady loads).

-Bill