Wire size for solar array???
 

Want to preinstall a conduit run for future PV roof array from my attic to basement main box during new construction. What gauge main feed wiring and how many would be required? I have 30'x20" of south 45deg pitch clear roof exposure.

Well, lets calculate . . . .

You have some 600 sq feet of roof size (20 x 30 ft). Assume you fill the roof completely with panels with each panel being about 18 sq feet each. About 33 panels (600/18).

Assume net output of 300 watts (high estimate per panel ) gives you about 10 kW (300 W x 33). P = Ei so the wattage is about 40 amps at 240 V.

Now the kicker is how far your wire run is. This current load is likely going to need 6 G stranded copper (NOT aluminum) and maybe 4G if it is a long run (> 75 feet).

Remember that L1 and L2 (each being the 120 V legs) need to be fat and thick (6 or 4 G). The neutral can be 8 or even 10G with 10 G for the ground (four wires total). The extra $ cost for thicker G wire is small considering safety and lower voltage drop .

I would use 1 inch conduit with a pull string installed. The above four wires can easily fit in this size conduit.

GREAT idea to do this now. Also excellent roof pitch for your latitude.

Hope this helps.


Steve

It will be a direct run from basement to attic two stories, about 25'. As I plan to grid tie if I'm doing any PV I might as well cover front of roof. I have to cross a couple of top and bottom plates so I'm not sure I have clearance for 1" but will try for it(may have to flattened it in some places). Is a ground wire required? I am still very uneducated in the wiring world of PV. Am concentrating currently on building of structure and learning hydronics for infloor heating.