Solar Panels 400ft From House....19360 KW system with 3 SMA SB 7.0-US inverters

Dan_C · November 2016

I'm trying to figure out how to get the power from my panels back to my house, with acceptable Voltage drop.

I'm wondering if I can run DC back to house with 3 x 2 Pairs of 4 AWG aluminum then hook to inverters, or should I have a breaker box and inverters out with solar panels and run the AC back on 350mm wire?......Thanks for the help in advance....Dan

animatt · November 2016

Your dc runs could be much higher voltage.
Each of your 3 arrays would be connected to roughly 6500w.
Run that at something like 450v. Would leave you with about 14.5 amps to move at peak power.(per array)

A pair of 10awg gauge copper wire could do that.

http://www.calculator.net/voltage-drop-calculator.html

At ac transmission you would be transmitting at 240v
That is 80 amps at peak. 1/0 should handle that approximately 100kmils

Price your options. Will you ever need or want ac power out by the array? If so transmitting via ac maybe benificial.

Dan_C · November 2016

Thanks for helping me on this.

So, I was trying to stay with alumninum for the 400ft long, and in order to maintain 3% Voltage drop or less, the tools were saying I needed like #250 aluminum or like 4/0 copper (which looks really expensive).

Is the 3% voltage drop the real target (as all the tools seem to say so) or can I go higher?

Here is output of the voltage drop tool..

Results

1 conductors per phase utilizing a #250 Aluminum conductor will limit the voltage drop to 2.64% or less when supplying 80.0 amps for 400 feet on a 240 volt system.

For Engineering Information Only:

205.0 Amps Rated ampacity of selected conductor

0.09 Ohms Resistance (Ohms per 1000 feet)

0.041 Ohms Reactance (Ohms per 1000 feet)

7.199999999999999 volts maximum allowable voltage drop at 3%

6.328. Actual voltage drop loss at 2.64% for the circuit

0.9 Power Factor

jonr · November 2016

For long runs, it makes economic sense to use higher voltage drops than for short runs.

westbranch · November 2016

AFAIK the 3% was established based on the (old) High cost of PV panels say 10 or more years ago.... So now with cheap PV prices, you need to do a calculation to see what the cost of losing 3% is vs the cost of adding another cheaper PV to send more watts to the inverter(s)....
Agree with all comments about sending higher DC current.
hth

animatt · November 2016

I get 1 awg copper would get you a 3.3% drop at 80 amps 240v
But a more realistic 65 amps 2awg copper gives a 3.39% drop

2/0 awg aluminum gives a drop of 3.28% at 80amps 240v

These are much smaller than what you thought you may need. But I am cheap and even 2awg is expensive to me.
3 pairs of 10awg cabling would do your 3 arrays.

So calculate rate of 1200ft [400x3] 2 conductors. 10awg.
Vs
400ft of 2

Only reason I see to do ac transmission is if you need ac power out that way anyway.
I am going to do an array at a similiar distance yours is. Mine will do ac transmission because I need power out there anyway.

mike95490 · November 2016

I would lean toward HV DC transmission, and if you need AC out there, drop in some 1/2 PVC and pull AC back out to there while you have a trench open. I think AC & DC can go in the same trench, but not in the same conduit.

Solar Panels 400ft From House....19360 KW system with 3 SMA SB 7.0-US inverters

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