Spare, extra or redundant, call it what you like, chances are you are going to need more. Oh, yeah, there’re fuses and connectors and such as that, but I’m talking about wire and cable, here.
When I was a young broadcast engineer at WCOA, Pensacola, I engaged in a total rework of its broadcasting facility. It was tricky, since the station had to stay functional while the new stuff was being installed. An important part of the installation was the rewiring.
At one time I could have told you exactly how much wire I pulled. I can’t now, but I can tell you it could be measured in miles. I handled so much wire that my forearms broke out in a rash from the PVC oil in the insulation. Lots of wire went everywhere there was a studio, including lots of spare wire. Every room had a junction box and active cables went to rack mounted patch bays. In addition to the normal arrangement, any studio could be patched into any other studio, for whatever purpose.
Well, plan as you may, you can’t think of everything, so we ran lots of extra wire in every direction. Sure enough, those extras started getting used. Amazingly, all the extras from Studio A to the AM control room soon got used. No problem! We’d just route through another room.
That kind of thinking stuck with me into my computer career. Every room in our new headquarters had cables going to a patch bay in the computer room and, sure enough, it wasn’t long before things started getting routed all over. Then came that new-fangled arcnet and ethernet stuff. We hadn’t even conceived of that when we built the place, but had left available access and pretty soon every room had both.
The same sort of thinking ahead can pay off in designing your solar power system, too. My Solar Shed is 200′ from the house, so it is a major pain to run a new line, especially considering there’s a water line in close proximity. In addition to the main power line, there is a conduit containing 5 cables, which are now in use, and a spare, empty conduit.
My limiting grid tie experiment is progressing and because of the versatility of the extra cables, I have been ok, so far. I am considering that empty conduit, but pulling stiff wire through 200′ of conduit is easier said than done. I actually have some 10″ and 12″ concrete pipe that would have made a wonderful conduit, had I thought about it. Boy, could I get some wire through that!
For an ordinary installation, you probably don’t need huge conduit, but consider putting in some extra cables and empty conduit. Sure, it is an extra expense if you never need it, but getting a trencher or backhoe to install new work without cutting up the old stuff can be expensive and even perilous.
OK, so your modules aren’t 200′ away, they’re on the roof. It will be pretty easy and cheap to install a combiner box that is a little bigger than your minimum requirement and to put a few extra runs of solar wire. Maybe even put in some small control or sensor cable in case something comes up where you want to monitor temperature or something else up there.
Leave access, too. My solar control room is also now my Man Cave. The ceiling and walls are all closed in where you can’t see the wires. There is yet another expansion of the Solar Shed planned, which may add 50 to 150 more modules. That means lots more wire, but it isn’t a problem. Wall panels around the control panel were installed with screws, so it will be easy to get the new wires run. The wall effectively becomes a raceway and raceway is much easier than conduits for channeling big bundles of wire.
The point of all this is to say, “think ahead” and make it easier on yourself in case you can’t think of everything.