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

Dan_C

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

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

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

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

westbranch

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

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

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.