Grounding in a hybrid solar setup.

[Eleison]

I've been doing a lot of reading and watching on this subject, including reading Filterguy's "Grounding Made Simpler", but despite that there's still a lot that I don't understand, and I'm probably going to use incorrect terminology, so forgive me in advance. Me am dumb.

I intend to build a small solar setup, but I'm debating on whether to connect it to the existing system, or whether to have it stay completely separate.
In particular I'm trying to understand how to ground the system properly. I'm wondering if I can use the 'AC In' of an AIO inverter to connect my loads, AND my solar panel frames/racking to true earth ground. Something like this:





There's a few things I'm unsure of though.

1: Is the 'AC In' of an AIO inverter always active? I'm not sure if it might disconnect when it's not charging for example.

2: Is it fine to have my panel frames attached to ground through all of my equipment? Even mounted on wood it's going to be sort of a grounding rod itself no?
Is it fine to allow any static build-up to discharge through my equipment like that?

3: I'd assume a nearby lightning strike would be really bad with this setup. If I attach a MidNite surge protector, would that be effective mitigation? Would I have to do that on both sides of the system?

And please point out anything I'm missing, I'm sure there is plenty.

 

[Hedges]

I prefer ground wire from PV panel frames going directly back to AIO.
Keep the ground wire together with current carrying conductors.
It also avoids breaking that ground if AC wires are worked on.

"Outlet" - meaning connected by a plug?
If unplugged, it loses connection to ground rod and loses N-G bond
I do that for bench testing, not use.

Is this 120V, or 120/240V split-phase?
Does it switch or bond neutral?

The grounding devil is in the details of the inverter, which isn't documented or linked here.

Both utility line and PV array can pick up lightning surges. Different model surge suppressors depending on voltage. Midnight is good.

 

[FilterGuy]

1: Is the 'AC In' of an AIO inverter always active? I'm not sure if it might disconnect when it's not charging for example.

That depends on the type of inverter. If your inverter is a hybrid inverter, then it can export as well as import power. However, the term AIO is not usually applied to a hybrid inverter.

In the more typical definition of an AIO, the AC in will only draw power. It can be used for both charging batteries or running the load in pass-through mode.

2: Is it fine to have my panel frames attached to ground through all of my equipment? Even mounted on wood it's going to be sort of a grounding rod itself no?
Is it fine to allow any static build-up to discharge through my equipment like that?

The NEC requires the panel frames be grounded to the same grounding system as the rest of the home. However there are two schools of thought on how to best do that.

1) Run the grounding wires of the solar array all the way to the main panel where the grounding rod is connected. This will help minimize any surge from a nearby lightning strike from getting into the rest of the houses electronics.

2) Run the grounding from the solar array back to the AIO. This will give the shortest path for any ground fault on the PV lines.
Note: There are some reports that flickering LEDs get worse if the PV is connected to the inverter. I don't have enough data to confirm that or refute it.

I typically use the approach in #1. Others believe it should be #2. The NEC allows either.

Either way, the frames are grounded and there will be no significant static build up.

3: I'd assume a nearby lightning strike would be really bad with this setup. If I attach a MidNite surge protector, would that be effective mitigation? Would I have to do that on both sides of the system?

Surge protectors will help but can't guarantee protection. A strike 20 ft away would probably blow a lot of things up even with surge protectors.

Yes, surge protectors at multiple places can help.

 

[Eleison]

I prefer ground wire from PV panel frames going directly back to AIO.
Keep the ground wire together with current carrying conductors.
It also avoids breaking that ground if AC wires are worked on.

I was under the impression that most inverters only have input for PV+ and PV-, that's why I was thinking I would have to attach the panel ground in a separate panel. Where does the panel ground go in an inverter?

"Outlet" - meaning connected by a plug?
If unplugged, it loses connection to ground rod and loses N-G bond
I do that for bench testing, not use.

Heh, that's why I put that there, I figured it was probably a bad idea.
I didn't even think about unplugging breaking the N-G bond. Good point, I'll not do that.

Is this 120V, or 120/240V split-phase?
Does it switch or bond neutral?

The grounding devil is in the details of the inverter, which isn't documented or linked here.

Both utility line and PV array can pick up lightning surges. Different model surge suppressors depending on voltage. Midnight is good.

No particular inverter, I wanted to figure this out before I committed to one.

Tyvm for the help

 

[Eleison]

That depends on the type of inverter. If your inverter is a hybrid inverter, then it can export as well as import power. However, the term AIO is not usually applied to a hybrid inverter.

In the more typical definition of an AIO, the AC in will only draw power. It can be used for both charging batteries or running the load in pass-through mode.

The ground connection in particular is what I was worried about losing connection to.

The NEC requires the panel frames be grounded to the same grounding system as the rest of the home. However there are two schools of thought on how to best do that.

1) Run the grounding wires of the solar array all the way to the main panel where the grounding rod is connected. This will help minimize any surge from a nearby lightning strike from getting into the rest of the houses electronics.

So that would look something like this right?

2) Run the grounding from the solar array back to the AIO. This will give the shortest path for any ground fault on the PV lines.
Note: There are some reports that flickering LEDs get worse if the PV is connected to the inverter. I don't have enough data to confirm that or refute it.

And that would look like this?

I typically use the approach in #1. Others believe it should be #2. The NEC allows either.

Either way, the frames are grounded and there will be no significant static build up.


Surge protectors will help but can't guarantee protection. A strike 20 ft away would probably blow a lot of things up even with surge protectors.

Yes, surge protectors at multiple places can help.

Ty!

 

[Hedges]

I was under the impression that most inverters only have input for PV+ and PV-, that's why I was thinking I would have to attach the panel ground in a separate panel. Where does the panel ground go in an inverter?

Mine have multiple screw terminals. If not, can join with split bolt or other appropriate connector.

Heh, that's why I put that there, I figured it was probably a bad idea.
I didn't even think about unplugging breaking the N-G bond. Good point, I'll not do that.

One of my models is supposed to be hard-wired only. I would just mount an outlet on it with neutral tied to ground. Unplug from the wall, plug into the N-G bonding outlet.

You should have it grounded either way, separate wire could do that. But if mobile application, usually not.
GFCI outlets are good for shock safety.

No particular inverter, I wanted to figure this out before I committed to one.

Many brands and models. Be sure to select one that fits your application, like native support of split-phase if that's your application, dynamic N-G bonding if mobile, etc.

Grid-tie net metering, grid-support, or just transfer switch.
Surge sufficient for your loads, etc.

Wide range of prices, like $800 to $8000.

 

[Eleison]

Mine have multiple screw terminals. If not, can join with split bolt or other appropriate connector.

I see, ty.

One of my models is supposed to be hard-wired only. I would just mount an outlet on it with neutral tied to ground. Unplug from the wall, plug into the N-G bonding outlet.

Sorry I'm confused. You mean the N-G bond is in the inverter, and you attach an outlet to the 'AC Out' of the inverter and plug whatever device into that?

Many brands and models. Be sure to select one that fits your application, like native support of split-phase if that's your application, dynamic N-G bonding if mobile, etc.

Grid-tie net metering, grid-support, or just transfer switch.
Surge sufficient for your loads, etc.

Wide range of prices, like $800 to $8000.

Yeah, I haven't narrowed it down too much yet. It's going to be relatively small, and immobile, but I haven't decided on whether I want to to be completely off-grid or not. I'm pretty new to this so it depends on how hard each one is haha.

 

[Hedges]

Sorry I'm confused. You mean the N-G bond is in the inverter, and you attach an outlet to the 'AC Out' of the inverter and plug whatever device into that?

When plugged in to the wall, inverter inherits N-G bond from your house wiring.
Unplugged from wall, its N and G are isolated.
If you took a bare outlet, wired its rear terminals N and G together, then plugging inverter into this isolated outlet gives it N-G bond.

Some people use a male plug with N-G bond for portable inverters, similar idea.

But either way, "ground" is just a wire. Would be nice to have some way to connect to ground rod or pipe.
External wire? Jumper cable clamp?

Yeah, I haven't narrowed it down too much yet. It's going to be relatively small, and immobile, but I haven't decided on whether I want to to be completely off-grid or not. I'm pretty new to this so it depends on how hard each one is haha.

Completely offgrid means oversize, doing without power sometimes, or a generator.
The grid is a large and reliable source.

What do you want to power? Refrigerator? A/C?
motors take 5x as much power to start, for about 1 second.
Some inverters are better at supplying surge than others.
Determining what to power upfront lets you buy suitable equipment.

You'll always run low on power at some point. It is useful to have battery state of charge indication, to automatically or manually turn off large loads. That's a feature of my inverters (2 levels of SoC to control relays.)

 

[Eleison]

When plugged in to the wall, inverter inherits N-G bond from your house wiring.
Unplugged from wall, its N and G are isolated.
If you took a bare outlet, wired its rear terminals N and G together, then plugging inverter into this isolated outlet gives it N-G bond.

Some people use a male plug with N-G bond for portable inverters, similar idea.

But either way, "ground" is just a wire. Would be nice to have some way to connect to ground rod or pipe.
External wire? Jumper cable clamp?

Ah okay, I think I gotcha.

Completely offgrid means oversize, doing without power sometimes, or a generator.
The grid is a large and reliable source.

What do you want to power? Refrigerator? A/C?
motors take 5x as much power to start, for about 1 second.
Some inverters are better at supplying surge than others.
Determining what to power upfront lets you buy suitable equipment.

You'll always run low on power at some point. It is useful to have battery state of charge indication, to automatically or manually turn off large loads. That's a feature of my inverters (2 levels of SoC to control relays.)

Well, when I say completely off-grid I just mean not connecting the electrical components. I'd still use the grid for most things. This system is just me dipping my toes in really, it would probably power A/C and a pc and not much else, but would serve as a bit of a back-up for lights/phone/etc in case of power outage.