Grounding question

Tropics · May 2020

I had the idea to build a very small system (2x20W panels) to occasionally charge 12V scooter batteries (36Ah)— no inverters— when my less than reliable local grid goes down.

Reading up about grounding has tripped me up though. I read one wants to ground the metal frames of PV panels. But:

1) this alerted me to the fact that the easy path I’d wanted to use for the power cables: from sunny 2nd floor roof to a spot on the 1st floor patio for the batteries (nicely sheltered from frequent rain but also nicely ventilated) goes by several metal objects: Flashing, a spiral stairway, a wrought iron fence, a gutter, a downspout. We also get frequent thunderstorms. In addition, the roof is reinforced concrete (with rebar) and I have no idea about that (!)

2) some of the above metal objects I could avoid with more cable ($’s), but not the stairs. I’m unclear if the spiral stairs being anchored some feet into the earth already counts as being grounded (?)

3) The easiest path to earth ground would appear to be the water main. This is only accessible via an opened door until I drill a hole into the concrete wall (the whole house is concrete walls), but I would want to delay that step till it’s clear this system made any sense. Without such a hole, I thought I might be able to use screw-in grounding lugs to the various bare metal surfaces and the water pipe & then open the door & hook up this grounding wire only when needed.

4) Or, I thought, I could decide NOT to site the panels on the sunny roof (where the sun always shines) and instead keep them in the patio at ground level, where the sun comes and goes, but that means it will produce less power obviously. I would have to measure/guesstimate the loss and feasibility. But I’d also only want to do this if the hazard of the alternative is sufficiently worse to make it not worth doing

BB. · May 2020

Welcome to the forum Tropics,

I guess you are in Puerto Rico? Is this your home, or are you renting (i.e., how much "work" can you do on the building)?

In general, anything that is hit by lightning will be destroyed... It is very difficult to make something lightning proof... So we are left with trying to make the "stuff" relatively safe for the people.

So, that means either intercepting the lightning first (lighting Rods on roof line, grounding cables down side of building to ground rods), or at least grounding (for example, the solar panel frame and mounting frames with 6 AWG minimum cable straight down the the outside of the building to an ~8 foot ground rod driven outside the foundation into the earth (look up grounding plates--A flat copper plate buried in the ground can be used instead of a ground rod if you have issues with driving the rod).

Lightning does not like to take sharp turns (a longer soft turn can be OK). Long cable runs (10+ feet horizontal to cold water pipe/inside the building) and the lightning will leave the copper cable and find another path. Lightning wants to go to the outside edges/walls of a building (don't put panel on middle of roof, and run ground cable down middle of building--You are bringing lightning into the building).

For the solar power wiring--If lightning is a big concern, can you keep the solar power and scooters/batteries on the outside of the (living space of the) building such as a lean to (or at least, to an internal space next to an exterior wall)? Again, don't bring the lightning into your interior living space (for safety). I think you are saying you can do this?

We had a poster in PR that got hit by lightning (no harm, no major damage). The discussion is here:

https://forum.solar-electric.com/discussion/7968/weird-thing-2

I will stop here--Your thoughts?

-Bill

Tropics · May 2020

Thank you. Yes, Puerto Rico, and I do own the house. Sounds like it’s complicated then!

For lightning I was thinking only about surges, when lightning strikes miles away during a storm— makes some of my lights flicker— but it sounds like lightning has been known to get up close and personal, too! There is no lightning rod on the roof right now.

Good to know though that twisty wire paths won’t work!

What I have is kind of an outdoor courtyard (no roof). It’s behind my house but there’s a very very tall party wall (we call it a “medianera”) separates it from the neighboring building (can’t see the other buildings unless you get on the roof). I was thinking maybe the wires could come down to this courtyard from upstairs, and go under the veranda, where it’s partly sheltered (meaning it doesn’t get wet in the rain).

But I’m starting to think my idea is sounding a little mickey-mouse, because it’s outside but also close enough to be still sort of “interior” (?), and definitely if the water pipe brings problems, that doesn’t work. Maybe solar this just isn’t a good fit for solar?

If the grounding plate/rods were already installed, it might make more sense, but to put them in I’d have to tear up a tiled floor in the courtyard and dig... Maybe it outweighs the advantage of the batteries? Maybe it’s better to keep this one a daydream than to jump in and do it 🤔 😀

BB. · May 2020

It really won't save you money (solar) vs your utility bill... However, if you have a working charging station when the power is out--May be worth it to you...

Obviously, I don't know your exact installation conditions. But as long as the wiring is "exterior" to your living space, less danger of human/lightning interaction.

Another option--You can install the panel on the roof, and have a weather proof plug connection (or sheltered under roof), and simply unplug and move the rest of the wiring around 10+ feet away from the panels. Then no worse than you have today (roof/vent pipes/etc. that can still get hit--Then what).

I am not trying to stop you from doing what you need--Just trying to point you to things you can research/change/etc. and possibly still meet your needs.

Another post with lots of lightning informaiton:

https://forum.solar-electric.com/discussion/comment/84242#Comment_84242

-Bill

Grounding question

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