Some suggestions on completing migration of panels to roof

Fenachrone

After almost 20 years of them sitting on a now-rotting home brew wood rack, I will be migrating my panels to the roof of my seasonal log cabin.  They will run portrait style across the bottom tier of the roof below the skylights.  They will be mounted with S5! SolarFoot fasteners with rails.

I will be using a Midnite Solar pre-wired combiner.  My thought is to mount the combiner  vertically on the left side of the cabin exterior, not too high up and accessible from the ground. 

My first question is, what sort of conduit, if any (plastic, non-metallic) is typically used to enclose the panel wiring (three strings worth) on its way to the combiner?  (I'll use clips under the panels running across the rails).

Then PVC conduit carrying the wire from the combiner box into my crawl space and up to my charge controller.   Is it still typical to use THHN wire for this purpose or is there a specialized product?   My maximum open circuit voltage should not exceed 200 v.

Distance from combiner box to charge controller will be no more than 25 ft.

Lastly, should the THHN running in the crawl space to the SCC also be housed in a conduit?

 Thanks for any assistance!

Graham Parkinson

Your roof is very similar to ours, even the same colour.  We are also using S5 clips on standing ridge roofing.

Code (at least here in BC, our part of Canada) is for DC wiring to be in metallic conduit (ie EMT) since DC sustains an arc unlike AC which quenches arcs during zero crossings.

In particular, DC wiring inside the house generally has to be in metallic conduit.  You'd probably want the wiring on the outside wall to the combiner to be in conduit as well (protection against squirrels etc.)

THNN wire is fine inside conduit.   There is specialized PV wire with extra thick UV resistant insulation for short exposed roof top connections like panel to panel, but better in general for roof top wire to be in conduit to avoid potential wind induced abrasion, critter and UV damage etc. 

You might get away with PV wire clipped under the panels for the run to the combiner but conduit makes for a much neater install.   Home Depot sells Oatey brand roof flashings that you can use for the roof penetrations at the eaves.

I've painted galvanized EMT conduit to match our roof and wall colours.  You need to clean it really well (use TSP, scotchbright pad) and prime it with etching galvanized spray primer.  The mini S5 clamps are good for mounting conduit on standing seam roofs.

Dave Angelini

20 year old panels?  What make/model? Have you looked at the cost of a quality new panel from the store here or elsewhere? A Tier 1 panel from a quality company can have 25+ years of product and power warranty.

Alot of work to have to do again, not to mention the damage to your roof. Why not rebuild the ground rack? Shading ?

Fenachrone

Thanks for the very good information, Graham.  I suspected metal conduit was the way to go, so will do that.  I believe S5! or IronRidge, who's racking I'm using with the S5! SolarFoot system, both have conduit attachment hardware.   Just a matter of putting the pieces together with the bends and turns.

I should have mentioned, Dave, I no longer have the original panels on that ground rack.  I have more recent stuff (GMA Solar) and and am bringing up even newer stuff this summer.  The story of the ground mount rack goes back to my needing a cheap solution to getting the panels set up in 2006, and by someone's recommendation I mounted them horizontally.  That's cost us serious power output with the exception of the middle of PEI's brief summer, when the sun is overhead.  Come fall, we get our butt kicked with that flat mounting.  My roof in the photo is south facing and with that angle we're going to do much better.   We have no shading whatsoever in our open field.  The posts of the ground mount are  getting shaky so the whole thing might collapse in the not-too-distant future.  I've gotten pretty good recommendations on the S5!Solar Foot system for metal roofs, and guys who did my roof job will be installing them.

Dave Angelini

Yes the S5 is used alot with good results and I have used it when I had to on a barn.

Just really want to emphasize how using a roof of the home offgrid is the last resort if it can be done on the ground.  My quote is only rainwater and some snow should get on your homes roof.

Good Luck!

Fenachrone

Well, at the very least I'll leave the post where the combiner box is located if I ever do anything on the ground again.  The conduit running to the house and the THHN will stay.  I looked at various approaches to new ground mounts.  All involved more work than I'd like to get into and costs as well.  The only mild benefit at this point might be increased adjustment to get a bit more solar output. 

The panels on the racks or the wires exposed underneath haven't been vandalized, but we had a break-in years ago.  I'm surprised someone hasn't screwed around with that rack because that's just what some people are inclined to do.   

Dave Angelini

If you have worries about security that is a different story. Too bad as that can really spoil offgrid life.

Snow on a roof panels can be a major issue of you live there full time. Sounds like you don't!  Good Luck !

Fenachrone

Thanks!  It is a seasonal residence.   Been 20 years with it, though, and not a single regret. 

Graham Parkinson

Fenachrome

I mislead you earlier by saying that the Canadian Electrical Code requires metallic conduit on roofs. 

 You should be able to use PVC conduit on your roof - If your conduit does not penetrate thermal insulation - which yours would not, if you run the conduit down off the roof through the eave and down a wall.

PVC conduit that runs through attic insulation needs to be protected by a sleeve to ventilate it and prevent development of excessive heat.

You are allowed to have exposed wiring on a roof if it is within the array, otherwise the wiring needs to be protected.

Fenachrone

Thanks for those clarifications, Graham.    That's right, there will be no roof penetrations of cables; they'll come right off the side and then into conduit, and PVC will be much easier to work with than metal conduit.