Solar system design notes

Jane’O is going solar! Here’s my checklist of what needs doing, and some calculations for planning purposes. I want to support about 800W of solar panels. I’m going to start with 400W and then increase capacity if necessary.

What I already have:

I intend to wire these, two in parallel, and two in series, giving a maximum of 11A at around 34V. If I add another pair, I’ll need to support more current -- 16.5A at 34V, and with a fourth pair, 22A. Running these numbers through the Blue Sea Circuit Wizard, with an estimated distance of 15 feet, shows that AWG 14 will work fine. If I do decide to go with all 8 panels, the solar controller will limit the current to 40A, but it will still give 40A even when a panel is shaded, so six panels may be a more practical limit with this setup anyway.

40A is a LOT of current at 12V. Just 5 hours at this rating is 200Ah, enough to run everything for the whole day.

Pumping 40A at 12V from the controller to the battery is going to need some 12 gauge wire though, even though they are pretty close together, since 14 gauge wire is limited to 35A, combined with the fact that this wire will be in the engine room, it’s best to not take too many chances here. I’m also terminating the connection directly at the battery bank, with a 40A fuse, in case the controller gets fried.

So, what’s left to do is:

  • Mount the solar controller on the wall. This will use some epoxy to secure some plywood against the starboard hull, then screwing the panel into the plywood.
  • Run a wire from the top of the bimini to the engine room. It looks like the best route is through the bimini arch, which means I have to drill a hole in the stainless steel tubing. There is already a wire there, but I believe I can snake a new one through with some steel fish tape. One end is terminated with a MC4 connector, the other just screws into the controller. I am going to have to remove some headliner to get to the tube end though. I have already ordered the wire, but it’s not here yet.
  • Build and run the cable from the controller to the batteries and the ground bus. As mentioned, this should be 12 gauge
  • Mount the solar panels on the bimini. I think I’d prefer to mount them with velcro stitched into the fabric and glued onto the panel, but I might settle on something else.
  • Run the RJ45 cable from the solar controller to the nav desk, so I can mount the MT-50 remote.
  • Run the temperature probe from the controller to the batteries. This part is super easy.

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