Distance from CC to Panels help

[teknatronik]

Hello, I have 4 255 watt solar panels.Maximum Power at STC* Optimum Operating Voltage (Vmp) Optimum Operating Current (Imp) Open Circuit Voltage (Voc) Short Circuit Voltage (Isc) Maximum System Voltage Maximum Series Fuse Rating 255 W 30.00 V 8.50 A 37.40 V 9.09 A Module Efficiency 16% 600 VDC UL 13 A

I have a 40amp renogy cc.

I need to go 60 feet from cc to panels. I am using 10awg now, but notice a difference. I moved my panels further to collect sun longer.

What wire would be best? From my research it seems 4 awg is what I need. Is this correct?

I run my panel in series and parallel. I bring in 16 amp right now at cc and roughly 50 volts. I get about 800 watts on a sunny day.

Thanks for any help.

[Mike90250]

You are running about 18A from the panels, if I understand your description correctly. 10ga is sufficient, 8ga would be great, 6ga is overkill

[teknatronik]

Excellent, using a calculator for wire size i kept getting 7 gauge. I will go with 8 gauge .

would i be okay using thhn wire from lowes or should i get pv solar wire?

[BackwoodsEE]

You might consider running pairs of 10 AWG from each 2-panel string to the combiner box, for a total of four 10 AWG wires. The combiner box would be located near your charge controller. Four smaller wires can be easier to work with than two bigger ones.

Because ohmic losses in wire increase with the square of the current, it's also more efficient to use separate wires for each string. For example, running 9A through 100 feet of 10 AWG wires (0.2 Ohms for the circuit from PV panels to the CC and back) would burn up 16.2 Watts for each string, for a total of 32.4 W. Running 18A through a single pair of 8 AWG wire (0.126 Ohms from PV to CC and back) would burn up 81.4 W. That's a significant difference when your maximum production is 800 W.

THHN/2 wire must be protected from exposure in conduit if run outside. If you bury the conduit in a place where cars don't drive over, it need only be 6 inches deep if rigid (IMC). Otherise, 18 inches deep. You could run EMT conduit aboveground if it's supported every ten feet. You can fit four 10 AWG wires in a smaller conduit than two 8 AWG wires.

My own system has 8 10 AWG wires plus a 10 AWG ground conductor traveling 150 feet in 1 1/4" IMC conduit to a combiner box right next to two charge controllers. When I get my next PV array in this summer, I will have four strings feeding two charge controllers.

[teknatronik]

If I understand correctly, when I combine two panels, Ill have two 10 awg wires coming from them?My 4 panels will have 4 10 awg wires to a combiner box?

[BackwoodsEE]

If I understand correctly, when I combine two panels, Ill have two 10 awg wires coming from them?My 4 panels will have 4 10 awg wires to a combiner box?

Yep. Two pairs of 10 AWG wires from each string of two panels in series, for a total of four wires.

If the charge controller is not solidly grounded but has both its inputs floating with respect to ground, then I believe you will also want to include an equipment grounding conductor (EGC) connecting the PV panel frames to ground. There has been a lot of controversy about PV grounding, however, and I don't claim any expertise there. I can just tell you I grounded my PV panels at the array and also ran an EGC to the equipment shed along with the positive and negative PV cables for grounding there along with the charge controller and inverter, and from there connected to the ground rod at the AC service entrance. The inspector liked seeing all the grounding I had in place, and I'll just try not to stand outside near the array when we get the occasional lightning storm.

You might look at using some 10/5 VNTC tray cable. As long as it's rated for direct burial (mine was), it should be OK and is very convenient to pull and work with.

[teknatronik]

From the combiner box to charge controller, do I use a larger wire?

Would you mind sharing a good combiner box? Google pulls up so much im not sure whats quality .

[Mike90250]

Midnight makes good combiners. You just decide what size breaker to put into it (order breakers seperatly)

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=9&productCatName=Combiners

I used the MNPV6 and got all my breakers (inverter, controller, 3 combiner strings) into the one box. Might not be kosher, but it's simple and good gear

[teknatronik]

Ive been thinking about this and wouldn't series my panels go over voltage? My c.c. is rated 150v.

So a string would be roughly 80 volts. 37.5 x2 . Ill have 2 strings.

[Sunking]

Ive been thinking about this and wouldn't series my panels go over voltage? My c.c. is rated 150v.

So a string would be roughly 80 volts. 37.5 x2 . Ill have 2 strings.

2S2P is perfect and Voc is well under the limits of 150 Voc.

Look up your panels Voc rating should be around 40ish volts. At 2S2P takes panel Voc x 2 x 1.25 = Adjusted Voc

Example 40 Voc x 2 x 1.25 = 100 Voc is less than 150 Voc. No problem. Vmp is used to calculate voltage drop.

[teknatronik]

Thanks mate

[teknatronik]

Basically, everything will double from what i have now . Its looking like a 32amp breaker would be ok. Does that sound right or should i go a tad bit larger?

then im thinking 8awg from combiner to c.c.

Am i in the right ballpark?

[teknatronik]

If im only using 2 strings, do i need a combiner box or can i run the 4 wires into the cc?

[Mike90250]

If the controllers terminals are rated for multiple wires, you "can". But that leaves you with no way for easy testing if you think a string has gone bad.

[teknatronik]

Max terminal size is 4 awg. Im not sure what two wires at 10 awg would be, but I can mesh them nicely .