Wire gauge to use for a 150 foot run

[MTinOH]

I am working towards putting in solar for a small cabin we are building in the woods. Since the sunlight is limited at the cabin, I plan on putting the solar panels in a transmission line easement (part of our land) about 150 feet away. This is the setup I was planning so far:

1 300W 24V Renogy Solar panel (not purchased yet)
MPPT 30a Controller (not purchased yet)
100Ah LifePO4 Battle Born battery (purchased)
2200W pure sine inverter (purchased) that will run to a circuit breaker

So, I was planning on putting the controller right by the panel (mounting it underneath maybe). What type of wire do I need to run from the controller to the battery back at the cabin? I'm thinking I will put it in PVC conduit and bury it, but wasn't sure what type and gauge of wire would be needed.

Thanks so much for any help anyone can lend. I'm open to changing anything I haven't purchased yet too, if I'm heading down the wrong road.

 

[HRTKD]

Using the wire calculator in the link below, you would need 4/0 cable from the solar charge controller to your cabin. That's 300' of 4/0 cable (round trip), assuming the solar charge controller was putting out 20 amps at 12v. (I'm not convinced that you'll get 30 amps from the solar charge controller with a single panel, but whatever.)

Alternate scenario: Two of those panels in series for 80 volts, the solar charge controller is at the cabin, not next to the panel. You can get by with 8 gauge cable instead. The higher voltage is key.

In both cases, I'm restricting the wire to a voltage drop less than 3%.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[MTinOH]

Using the wire calculator in the link below, you would need 4/0 cable from the solar charge controller to your cabin. That's 300' of 4/0 cable (round trip), assuming the solar charge controller was putting out 20 amps at 12v. (I'm not convinced that you'll get 30 amps from the solar charge controller with a single panel, but whatever.)

Alternate scenario: Two of those panels in series for 80 volts, the solar charge controller is at the cabin, not next to the panel. You can get by with 8 gauge cable instead. The higher voltage is key.

In both cases, I'm restricting the wire to a voltage drop less than 3%.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

Great, appreciate the advice. Seems like not a great situation since a 4/0 wire seems pretty huge and expensive.

Is there any disadvantage to having the controller at the cabin vs by the panel?

Also, how is it that two 24V panels wired in series would equal 80 volts? It doesn't just double it to 48?

Thanks again.

 

[Forbisher]

Also, how is it that two 24V panels wired in series would equal 80 volts? It doesn't just double it to 48?

24V is only a general catergory and not actual panel voltage.
Look at the sales page for the so called "24V" Renogy 300 watt panel for the actual voltage specs.
Voc
Vmp
Imp
Isc
The Voc must be 40V if 80V is two panels in Series. I cant be bothered to check.
To calculate voltage drop do not use Voc.
Use Vmp.
You could buy 2 or 3 lower wattage panels to be series connected that have a high Vmp to increase voltage and let you use smaller AWG cables.
Hopefully your 150 foot estimate is accurate.

 

[HRTKD]

I made up the 80v, assuming it was close to what my panels are rated at. It was an example to show that a higher voltage reduced the need for the larger gauge wire.

 

[MTinOH]

24V is only a general catergory and not actual panel voltage.
Look at the sales page for the so called "24V" Renogy 300 watt panel for the actual voltage specs.
Voc
Vmp
Imp
Isc
The Voc must be 40V if 80V is two panels in Series. I cant be bothered to check.
To calculate voltage drop do not use Voc.
Use Vmp.
You could buy 2 or 3 lower wattage panels to be series connected that have a high Vmp to increase voltage and let you use smaller AWG cables.
Hopefully your 150 foot estimate is accurate.

I see, very helpful. Didn't realize that 24V didn't really mean 24V.

I like your suggestion of getting lower wattage panels and connecting them in series. Looks like if I were to get the 4 100W Renogy panels it would be 17.9V (VMP) x 4 so about 72V. The panels appear to be 6 amp, so if I used the calculator right, it looks like I could get away with a 10 AWG wire. The controller would have no problem with the amperage in this instance I assume, but what spec would tell me if it could handle the voltage?

 

[Hedges]

Get higher wattage (and maybe higher voltage, like 36 or 48V) panels, connect them in series, and use 12 awg to save money?
If 3% loss is a rule, rules were meant to be broken.
(just don't break the "max Voc on a cold day" rule or you'll regret it.)
Get some SCC like from Midnight, and they let you bend the Voc rule on cold days.

 

[MTinOH]

Get higher wattage (and maybe higher voltage, like 36 or 48V) panels, connect them in series, and use 12 awg to save money?
If 3% loss is a rule, rules were meant to be broken.
(just don't break the "max Voc on a cold day" rule or you'll regret it.)
Get some SCC like from Midnight, and they let you bend the Voc rule on cold days.

Interesting thought but wouldn't the higher wattage panels and the larger controller far outweigh the cost savings on the wiring?

 

[Hedges]

PV panels are getting to be the cheapest part of the system.
Charge controller just needs sufficient Voc headroom.
Copper is expensive.

I've paid $100 for a 327W SunPower panel, but some people pay $50 or $37 for a 250W panel.
I've also paid $220 for a 500' spool of 6 awg, $54 for 500' of 12 awg.

Power lost in wire goes as I^2 x R. Current is at peak only under ideal weather, time of day, season.
If I design a remote PV array for 10% or even 33% peak loss, average loss is considerably lower.

In the end, it is only money. Usually the goal is to produce the most power per dollar. Maybe, on the worst day produce the most power per dollar.

 

[A.Justice]

1 300W 24V Renogy Solar panel (not purchased yet)
MPPT 30a Controller (not purchased yet)

I would use a higher panel voltage, especially with MPPT. I use 55 volt panels to charge a 12 volt system, the MPPT converts the extra voltage into amperage. It would save you A LOT of money to use higher voltage, and smaller wire. Plus, with 55 volts, I can have quite a bit of acceptable loss.

 

[MTinOH]

I would use a higher panel voltage, especially with MPPT. I use 55 volt panels to charge a 12 volt system, the MPPT converts the extra voltage into amperage. It would save you A LOT of money to use higher voltage, and smaller wire. Plus, with 55 volts, I can have quite a bit of acceptable loss.

Thanks for the feedback. Any recommendation for higher voltage panels? Do you need an expensive MPPT to handle the higher voltage?

 

[MTinOH]

PV panels are getting to be the cheapest part of the system.
Charge controller just needs sufficient Voc headroom.
Copper is expensive.

I've paid $100 for a 327W SunPower panel, but some people pay $50 or $37 for a 250W panel.
I've also paid $220 for a 500' spool of 6 awg, $54 for 500' of 12 awg.

Power lost in wire goes as I^2 x R. Current is at peak only under ideal weather, time of day, season.
If I design a remote PV array for 10% or even 33% peak loss, average loss is considerably lower.

In the end, it is only money. Usually the goal is to produce the most power per dollar. Maybe, on the worst day produce the most power per dollar.

I see, thanks for your perspective. Yeah, I'm hoping to make it so I only have to use 10 AWG or so wire, otherwise it gets cost prohibitive. I'll have to look around to see if I can find deals on higher wattage panels.

 

[A.Justice]

I use a Victron 100v / 30a, it was around $250. A good charge controller is WELL worth the extra few bucks. My old PWM would give me around 5-8 amps max, and the higher voltage MPPT goes over 20 regularly.

I have some older Sanyo panels I got used off of LetGo. They were part of a high voltage, long cable run, grid tied system.

 

[Hedges]

Thanks for the feedback. Any recommendation for higher voltage panels? Do you need an expensive MPPT to handle the higher voltage?

I bought 36V 327W Sunpower from Santan solar.
I've see 48V 427W Sunpower from other sellers (for $150)

If you're only buy one panel, large ones will cost as much for shipping a pallet on a truck, so better with local source. (even better, buy and use a quantity, like 2kW to 5kW of them so shipping charges don't matter)

Midnight has 150Voc to 250Voc charge controllers, good for 800W to 4kW depending on battery voltage. Cost up to $1000.

Santan has a 200V charge controller for $323

Epever 8420AN 80A MPPT Solar Charge Controller - SanTan Solar Store

Buy our Epever 8420AN 80A MPPT Solar Charge Controller for only $380. Click the link to start shopping today!

store.santansolar.com

100V for $80

Epever 2210 20A MPPT Solar Charge Controller - SanTan Solar Store

Buy our Epever 2210 20A MPPT Solar Charge Controller for just $85. Click the link to start shopping today!

store.santansolar.com

Guess you can buy a decent amount of copper wire for the $250 difference!

 

[MTinOH]

I use a Victron 100v / 30a, it was around $250. A good charge controller is WELL worth the extra few bucks. My old PWM would give me around 5-8 amps max, and the higher voltage MPPT goes over 20 regularly.

I have some older Sanyo panels I got used off of LetGo. They were part of a high voltage, long cable run, grid tied system.

OK, does it seem like a reasonable solution for me to set up the following?

Two 200W 24V solar panels: https://richsolar.com/products/200-watt-24-volt-solar-panel
40a MPPT Controller: https://richsolar.com/products/40-amp-mppt-solar-charge-controller

The panels in series would be then be 75V and the max input for the controller says it is 100V. If I'm using the calculator right, I could then do the 150 foot run with 12 AWG wire and my voltage drop would only be 2% (maybe I'll use 10 so there is room for expansion).

 

[HRTKD]

Using the calculated I provided in post #2, 12 gauge wire would have almost a 4% drop. Did you use 150' or 300' for the length? That calculator expects you to provide the round trip distance, not the one-way distance.

The solar charge controller you linked to will work for those panels.

 

[Hedges]

4% drop? Only during peak power output from a PV panel?
Perfect. Sounds like 12 awg is the economical choice.
Would be OK as well with twice the panels, but if 10 awg is affordable, go for it.

 

[MTinOH]

Using the calculated I provided in post #2, 12 gauge wire would have almost a 4% drop. Did you use 150' or 300' for the length? That calculator expects you to provide the round trip distance, not the one-way distance.

The solar charge controller you linked to will work for those panels.

Oh jeez, you are right. I used the one way. Thanks for checking my math. Looks like I would be better off using a 10 gauge wire with that setup.

 

[Hedges]

Oh no! You lost all of 4% out of 400W (STC) of PV!
That's 16W.
With 10 awg instead of 12 awg, you'll reduce the loss to only 10W.
So you can save 6W (at peak production), about $1 to $3 worth of PV panel capacity ... for how much copper wire cost? I'm guessing $25?

 

[Forbisher]

The panels in series would be then be 75V and the max input for the controller says it is 100V. If I'm using the calculator right, I could then do the 150 foot run with 12 AWG wire and my voltage drop would only be 2% (maybe I'll use 10 so there is room for expansion).

10 AWG at 2.4% drop per the calculator below.
You can play with the numbers.

But 2 of those 200w Renogy panels in Series are 90.8Voc so cold weather would put you right at 100V

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net