Need help on a few things for off grid solar setup

BB.

Running the numbers:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&voltage=75.6&phase=dc&noofconductor=1&distance=55&distanceunit=feet&amperes=54&x=68&y=4

Voltage drop: 2.35
Voltage drop percentage: 3.11%
Voltage at the end: 73.25

2.35v * 54a = 127 Watts loss

You will need to check the NEC (electric code)--54 Amps may exceed 6 AWG wire capacity depending on insulation, conduit, etc. that you use.

-Bill

vtmaps

justinlee said:

so i guess looking into the future.....if i ran 6 awg now.......changed the charge controller to 60 + amp...doubled the array....too 4160 watts 54 amps @48 volts....would that 6 awg be enough making it a wise decision to run bigger wire now?

If you doubled your array and used 6 gauge cable you would have a 3.24% voltage drop and a cable loss (at full power) of 135.1 watts.

BUT that would be folly.  You could do much better.  Rather than doubling the array and getting a larger controller, you would be MUCH better off putting up a second array and buying a second controller for it.  Thus, rather than putting in a 6 gauge cable now, put in two 8 gauge cables.  You will have more flexibility in the future. 

The reason I suggest you do not double your array is that it is already compromised... it is probably the best way to use the 16 panels you have.  If you had 15 (or 20) of those panels, you could put them in three (four) strings of 5 panels.  Your string voltage would be 18.9 volts higher (less cable loss), but not so high as to cause inefficiency in the MPPT controller.  In fact, your solar harvest may go up because you are giving the controller a bit more headroom in which to sweep and find the max power point.  On a hot day your string Vmp of 75.6 volts is reduced... if you are trying to put 60 volts into your battery and your array is only putting out something in the low 60's, your controller doesn't have much headroom. 

And if you are planning on another 2000 watts of panel, with a second controller and cable you could use less expensive, "grid-tie" panels.  These panels are usually in the 200-300 watt range with a Vmp of about 30.  In a 48 volt system they work well when they are 3 in series.

--vtMaps

edit: I didn't see Bill's response before I posted... he is quite right about the ampacity being near the limits with the 6 gauge.  If you reconfigure the array to a higher Vmp (5 in series), you will reduce the current in the cable and 6 gauge will suffice.  That would mean 'doubling' your array from 16 to 30 panels.   That said, I still think a second cable, array, and controller makes more sense.

justinlee

Okay I have thought of a different idea here see what you think about this. If I run the battery shed right next to the panels and decide to run the AC wire from the inverter the 55 foot run would that be a better idea and more cost-effective

vtmaps

justinlee said:

Okay I have thought of a different idea here see what you think about this. If I run the battery shed right next to the panels and decide to run the AC wire from the inverter the 55 foot run would that be a better idea and more cost-effective

That is certainly a possibility, and is often done for really long runs.  If you're only running 120 volt AC, then you don't really gain all that much over running 90 volts DC string voltage.  If you are running 240 volts AC, then you will end up losing power in the step-down transformer that you will need at the house to make 120 volt AC.

What's your concern?  55 ft is not a terribly long run, and the cost of 55 ft of heavy cable is only a tiny fraction of the cost of the system.

As for losing power in the cable... nothing is 100% efficient, not the controller, not the cable, certainly not the panels.  We are fortunate that panels are so inexpensive now.  If you're worried about losing fifty or a hundred watts in the cable, it may be just as cheap to buy an extra panel as to buy a thicker cable.  And remember, those calculated power losses in the cable are at full nameplate power... the real losses will be much less. 

--vtMaps

justinlee

I appreciate that info but my concern is we have decided to put the battery shed next to the panels because next to the house it would be blocking the kitchen double windows so I probably will be running AC under the ground to the house from the shed

justinlee

I believe that Morningstar mppt charge controller monitor comes with a 30 foot cord... I kind of need it around 55-60 foot if I do it this route to keep the monitor In the cabin do they sell a chord for it that is that long

BB.

One thing to remember--Is you will probably going out several times a week to check on the battery bank (water levels, specific gravity possibly), start a the backup genset (in winter, poor weather), etc.

Would you like to have the system component close to the house, or you do not mind the walk?

-Bill

justinlee

I don't mind the walk it's no big deal it's just that while being inside of the house during the day at least from the start I want to monitor everything really close to see how things are going so I definitely want my monitor put inside the house but I looked around and found out that it is just a four wire cable similar to phone cord and I will just have to purchase a 60 foot or so cord for the charge controller monitor

vtmaps

justinlee said:

I don't mind the walk it's no big deal it's just that while being inside of the house during the day at least from the start I want to monitor everything really close to see how things are going so I definitely want my monitor put inside the house but I looked around and found out that it is just a four wire cable similar to phone cord and I will just have to purchase a 60 foot or so cord for the charge controller monitor

Make sure you put the monitor cable in a separate conduit... do not run the monitor cable with the AC cable.

--vtMaps

justinlee

Oh really I'm glad you told me that because I sure was going to put it in the same conduit I was worried about interference

BB.

Interference is a "possibility"... The real reason is for electric code. All cables in a tray/conduit are supposed to have the same insulation and "service type" (i.e., 120/240 VAC power from your inverter to house breaker box) vs low voltage (battery voltage, solar array voltage, electronic communications). Different classes of cables are supposed to be in different conduit.

-Bill