Incorporating a Lightning into an existing PV system - without HIS

[ridgebackpilot]

A neutral switch (Generac 6852?) appears to be the safest way to remove the bond to ground in the Lightning Pro Power generator:

Interestingly enough, I noted recently that the Tesla Gateway 2, which manages my solar array, Powerwall batteries, and grid connection, also has the ability to accommodate generator input.

More importantly for us, it also allows the installer to "remove the neutral-ground bonding strap" if necessary. (See page 8 of these quick install instructions).

My solar contractor that installed my system will be back here soon and I'm going to ask them about this.

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[ridgebackpilot]

Here's how one major Tesla Powerwall installer says the system will work with a backup generator:

 

[Henry Ford]

I am having trouble putting all this together.

This is from the Sol Ark 12 owner’s manual:
The system must have Ground connections and Neutral connections. Ground MUST be bonded to Neutral ONLY ONCE in the circuit.

And this is from the Lightning manual:
Grounding Type
Neutral Bonded

The neutral of the inverter generator is bonded to system ground. Connecting loads that also have neutral bonded to ground causes the ground fault detection to trip.

A neutral switch (Generac 6852?) appears to be the safest way to remove the bond to ground in the Lightning Pro Power generator:


I have a working system with both a critical loads panel and automatic transfer switch:

But to avoid messing things up and to take advantage of the Sol Ark’s ability to recharge my AGM batteries (260ah) it would seem my only option is installing a neutral switch in the circuit between the truck’s 240v outlet and the connection to the Sol Ark generator port?

In basic terms, any neutral that touches the truck system cannot touch any ground anywhere else. This means each circuit you want powered by the truck needs to have it's neutral pulled and connected to a switch.

To my untrained eye, if you wanted to use your truck to power your house you should pull select circuits from your critical load panel and install a manual transfer switch. Your whole system would work however it currently works but you'd have the option to power your house if it wasn't enough.*

* This is probably bad advice. I'm an idiot, talk to an electrician.

 

[v2h8484]

I am having trouble putting all this together.

This is from the Sol Ark 12 owner’s manual:
The system must have Ground connections and Neutral connections. Ground MUST be bonded to Neutral ONLY ONCE in the circuit.

And this is from the Lightning manual:
Grounding Type
Neutral Bonded

The neutral of the inverter generator is bonded to system ground. Connecting loads that also have neutral bonded to ground causes the ground fault detection to trip.

A neutral switch (Generac 6852?) appears to be the safest way to remove the bond to ground in the Lightning Pro Power generator:


I have a working system with both a critical loads panel and automatic transfer switch:

But to avoid messing things up and to take advantage of the Sol Ark’s ability to recharge my AGM batteries (260ah) it would seem my only option is installing a neutral switch in the circuit between the truck’s 240v outlet and the connection to the Sol Ark generator port?

Putting a neutral transfer switch on the generator port won't resolve the F150 GFCI issue. Your house wiring (connected via the grid and load ports) still has a neutral-ground bond. You could put an isolation transformer on the generator port and that should resolve the F150 GFCI issue and be code compliant.

 

[world2steven]

Putting a neutral transfer switch on the generator port won't resolve the F150 GFCI issue. Your house wiring (connected via the grid and load ports) still has a neutral-ground bond. You could put an isolation transformer on the generator port and that should resolve the F150 GFCI issue and be code compliant.

Thanks! If I did the math right, an appropriately sized isolation transformer (7.5kVA?) isn't cheap, about $3k on Amazon. Since actually needing to do this will hopefully be seldom to never I'm thinking the best real-world solution is removing the grounding pin in the connecting cord. There is apparently a safety issue - how serious is it? Can I get an electrician to do it if it violates code?

 

[Zprime29]

Can I get an electrician to do it if it violates code?

Can't speak for everyone, but personally I would not trust an electrician that is willing to do something that violates code.

 

[Henry Ford]

Thanks! If I did the math right, an appropriately sized isolation transformer (7.5kVA?) isn't cheap, about $3k on Amazon. Since actually needing to do this will hopefully be seldom to never I'm thinking the best real-world solution is removing the grounding pin in the connecting cord. There is apparently a safety issue - how serious is it? Can I get an electrician to do it if it violates code?

When doing research on this I came across the term, "bolted hot ground fault." I didn't have to search long to figure out it is not something I want to risk. Sure, it would be an extraordinary situation that put utility transformer current on something that a human would touch but it's an extraordinary circumstance when you are on generator power.

 

[v2h8484]

Thanks! If I did the math right, an appropriately sized isolation transformer (7.5kVA?) isn't cheap, about $3k on Amazon. Since actually needing to do this will hopefully be seldom to never I'm thinking the best real-world solution is removing the grounding pin in the connecting cord. There is apparently a safety issue - how serious is it? Can I get an electrician to do it if it violates code?

$3K sounds high. Here is a cheaper one https://www.zoro.com/acme-electric-transformer-75kva-120240v-wall-t279745s/i/G3052095/. If you are OK with used one then you can find one on eBay for less than half the cost of a new one.

I doubt any electrician would knowingly violate code, certainly not for a small job. A potential risk without connecting the ground is shock hazard. Frankly, compared to the cost of your Sol-Ark/batteries and Lightning it seems odd that you would consider a code violation for a relatively tiny savings.

 

[world2steven]

Putting a neutral transfer switch on the generator port won't resolve the F150 GFCI issue. Your house wiring (connected via the grid and load ports) still has a neutral-ground bond.

I don't understand this. Asuuming a neutral transfer switch would solve the ground fault issue between the Lightning (generator) and the Sol Ark (?), the Sol Ark must already have solved any issues between itself and the house wiring (connected via the grid and load ports)?

 

[v2h8484]

I don't understand this. Asuuming a neutral transfer switch would solve the ground fault issue between the Lightning (generator) and the Sol Ark (?), the Sol Ark must already have solved any issues between itself and the house wiring (connected via the grid and load ports)?

For clarification, the context for the isolation transformer suggestion is based on your idea of putting the Lightning on the Sol-Ark generator port in the above diagram you provided which has no neutral transfer switch. The neutral and ground are hardwired between the Sol-Ark and house wiring (on the grid and load ports) and Sol-Ark relies on the installer to make sure there is only one neutral-ground bound in the whole system. To meet this requirement when using the Lightining without isolation transformer, the Sol-Ark must not be connected to the neutral from the house wiring on any port.

So, assuming you want to connect the Lightning to the Sol-Ark generator port without isolation transformer then one solution would be to change the Generac ATS on the Sol-Ark load port to a neutral transfer switch and put a 3-pole contactor on the Sol-Ark grid port that must be turned off when the Lightning power is on.

 

[Maquis]

For clarification, the context for the isolation transformer suggestion is based on your idea of putting the Lightning on the Sol-Ark generator port in the above diagram you provided which has no neutral transfer switch. The neutral and ground are hardwired between the Sol-Ark and house wiring (on the grid and load ports) and Sol-Ark relies on the installer to make sure there is only one neutral-ground bound in the whole system. To meet this requirement when using the Lightining without isolation transformer, the Sol-Ark must not be connected to the neutral from the house wiring on any port.

So, assuming you want to connect the Lightning to the Sol-Ark generator port without isolation transformer then one solution would be to change the Generac ATS on the Sol-Ark load port to a neutral transfer switch and put a 3-pole contactor on the Sol-Ark grid port that must be turned off when the Lightning power is on.

Another option would be to add a manual transfer switch (switched neutral) in between the auto transfer switch shown and the critical loads panel.

I don’t like the isolation transformer due to cost, losses, and I wonder if the Lightning inverter can handle the inrush current of that big a transformer without shutting down.

 

[world2steven]

IIRC I discussed transfer switches with an EE who concluded it would be dangerous because of potentially different voltages in the power supplying my home grid from circuits not supplied by the critical loads panel & Lightning battery when the grid comes back on line?

The quick and dirty solution to using the Lightning battery in a prolonged a power outage (which hopefully will seldom or never occur) still appears to be removing the ground pin from a connector cable. Having the connecting circuitry in place would allow me to just add a generator if it became necessary. But which kind, floating or bound neutral? I don't believe the Sol Ark documentation says?

Presumably, floating neutral? If not, what's the difference between the Lightning's 'bound neutral generator' and an off-the-shelf model?

 

[Maquis]

IIRC I discussed transfer switches with an EE who concluded it would be dangerous because of potentially different voltages in the power supplying my home grid from circuits not supplied by the critical loads panel & Lightning battery when the grid comes back on line?

That could only be an issue if any circuits from the different panels are bootlegged together. That would be a real hack. Unless you have some wiring that was done by some hack handyman, there’s virtually zero chance of that.

 

[v2h8484]

For clarification, the context for the isolation transformer suggestion is based on your idea of putting the Lightning on the Sol-Ark generator port in the above diagram you provided which has no neutral transfer switch. The neutral and ground are hardwired between the Sol-Ark and house wiring (on the grid and load ports) and Sol-Ark relies on the installer to make sure there is only one neutral-ground bound in the whole system. To meet this requirement when using the Lightining without isolation transformer, the Sol-Ark must not be connected to the neutral from the house wiring on any port.

So, assuming you want to connect the Lightning to the Sol-Ark generator port without isolation transformer then one solution would be to change the Generac ATS on the Sol-Ark load port to a neutral transfer switch and put a 3-pole contactor on the Sol-Ark grid port that must be turned off when the Lightning power is on.

Based on the 240V only load test results (https://www.f150lightningforum.com/forum/threads/using-lightning-as-a-generator.14994/post-309716) with the Lightning, I am now also confident you can use an autotransformer instead of an isolation transformer to connect the Lightning to the Sol-Ark generator port with connected ground without issue. The advantages of autotransformer over isolation transformer includes significantly smaller, lighter, more efficient and cheaper. Autotransformer (and isolation transformer) will also automatically balance the loads across the 120V legs. Here is a video () that demonstrates the premature overload tripping problem (starting ~11:20 mark in the video) due to load imbalance that would be prevented with an autotransformer to allow usage of full power capacity of the Lightning.

 

[ridgebackpilot]

Very helpful discussion. Not being familiar with transformers, can someone post an example of an autotransformer that might work in this context?

And how would it be connected between the Lightning and the Sol-Ark or some other hybrid inverter or gateway controlling a solar power system?

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