Future solar conduit

[T-Bolt]

I will probably have my interior finished before I get around to doing solar. I would like to run a conduit from my roof to the basement for future use. Does anyone know what size conduit I should run for a solar system up to 2,000 Watts?

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[Iceni John]

I have 2040W of panels in two separate individually-tiltable arrays on either side of a central walkway between my two roof hatches. Each array of four panels has its own fused combiner box, from where 4AWG positive and negative cables run through the roof ribs down to the 50A breakers and charge controllers under the floor. Because each array is wired in parallel, their Isc is about 34 amps, so 4AWG welding cable will cause negligible voltage loss. I use aluminum weather-tight Bell boxes bolted to the roof under the walkway that each contain four 12A fuses and two busbars for pos and neg, and the 4AWG cables run from there without interruption to the breakers and charge controllers. Getting the cables from the lower ends of the roof ribs down to and through the floor was a challenge, but I now have continuous conduit to allow easy cable replacement if ever needed.

Don't use too small a cable for any low-voltage high-current applications. If in doubt, go larger! And use a proper circumferential crimper to attach the cable lugs - cheapo hammer-type crimpers are not enough!

John

[PNW_Steve]

Using John's example, with 4 x #4AWG conductors would require a minimum of 1" conduit.

I would suggest that you go a bit larger to accommodate future needs.

Google "conduit fill calculator" and you will find resources that will explain how to determine conduit sizing.

[BlackJohn]

Can you describe the route from the roof to the basement, totally outside the passenger compartment or going inside as well?
Going bigger in conduit size isn't a lot more money in any event. Bigger pipe makes for better and stronger attachment of supports and straps.
I'd go minimum 2" with suitable weatherproof fittings.

John

[JDOnTheGo]

Originally Posted by T-Bolt

Does anyone know what size conduit I should run for a solar system up to 2,000 Watts?

I admire planning! I am here to complicate it!!!

If you run high voltage panels, you can use much smaller cable (and an MPPT charge controller). I'm living on 1700 watts running down #10 cable at 60 volts. This doesn't sound like a big deal until you start pricing those big thick copper cables - then you might become interested.

[Iceni John]

Sorry, I forgot to say that I run the two 4AWG pos cables down one side of roof ribs, and the two negs down the other side. This way I can easily fit two cables per rib, and there's no risk of pos and neg being too close to each other inside the combiner boxes. Two 4AWG cables fit very nicely inside a roof rib.

John

[Iceni John]

Originally Posted by BlackJohn

Can you describe the route from the roof to the basement, totally outside the passenger compartment or going inside as well?
Going bigger in conduit size isn't a lot more money in any event. Bigger pipe makes for better and stronger attachment of supports and straps.
I'd go minimum 2" with suitable weatherproof fittings.

John

I've covered over two windows on each side, and my solar cables and PEX water lines run through them. Crown's construction is very different to other buses', which made it a challenge to put the cables where I wanted. The roof ribs end at longitudinal structural beams above all the windows, and the bodyside ribs start at these beams and extend down to the bottom of the bodyside. This means that I had to bore 1" holes through the beams' 3/8"-thick 90,000 PSI steel to make continuous runs for the cables and PEX, then run them inside the polyiso insulation between the blanked-off windows' inner paneling and outer skin, then through the window sills and down about one foot inside Crown's Dry Wall side walls before coming back through to the inside, then through the chair rails, than back inside the walls to go down through another massive steel stringer that connects the bodyside and floor, and finally for them to resurface inside the underfloor luggage bay where the breakers and charge controllers live. It sounds complicated, and it is! However, the cables and PEX lines are completely protected and out of sight, yet can be replaced if needed without (I hope) too much drama.

And if you're wondering about my mention of PEX water lines, I have a cold water line running up to the roof to feed two quick-connect outlets on the walkway for a washdown hose and brush - this makes cleaning the solar panels easy and safe. Instead of dragging hoses or heavy buckets of water up to the roof, I just open the front roof hatch, climb up through it onto the roof's central walkway, plug in my washdown brush and in a few minutes all my panels are squeaky clean. I also have another cold line running up to the roof and a hot return line coming back down from the roof, both of them for my eventual solar water heating panels that will occupy the last few feet of space after the last PV panels. These water panels will also be hinged to the walkway like my PV panels are, then they can be tilted up to 45 degrees above horizontal for better performance in the winter when the sun is lower.

Yes, it's been a lot of work to make everything this way, but I feel it's the best possible way for my needs. I'm only doing this once, so I'll do it the best way I can.

John