Multiple Tesla Powerwall 2's in parallel

[Grouch1980]

I tried looking online for wiring diagrams of multiple Tesla Powerwall 2's connected in parallel, but could only find installation pics, not actual wiring diagrams, such as the following:



My questions are (in an AC coupled method):
1. Doesn't each battery have its own integral multi-mode inverter? If so, are they programmed so that only one of the inverters integral to the battery is the master inverter, and the others follow it (with regards to frequency, timing, etc.)?
2. How is the output wiring of each battery interconnected together? I doubt they are just spliced together. How do they all connect to the backup loads panel?

Thanks.

 

[wwhitney]

1) There's a communications line that connects together the Gateway and all of the Powerwalls. Not sure of the details beyond that.

In particular, each Powerwall has an inverter that can operate as grid-interactive or as a microgrid. For grid-interactive mode, the computer in the Gateway tells the Powerwalls how much current to charge or discharge, based on the configuration and the data gathered by the CTs installed.

But in microgrid mode, I'm not sure if the coordination method among the Powerwalls involves the communications line or not. I believe the Gateway's involvement is limited to saying "yes, the grid is disconnected, it's OK to operate as a microgrid."

2) There's a combiner panel that has a 30A breaker for each Powerwall. The Backup Gateway 2 has provisions for an internal panelboard in addition to the MID, so often the combiner panel is internal to it, and may include the PV interconnection as well.

As to the overall topology, for residential it is typically what I think of as an H topology. The center line of the H is the Backup Gateway 2; then the ends of one side of the H are the service and the non-backed up loads panel (if any); the ends of the other side of the H are the generation panel (Powerwalls and PV if present) and the backed up loads panel. On a 200A service, the entire H could be a multi-segment 200A feeder.

Cheers, Wayne

 

[Grouch1980]

Is another option to use a stand-alone combiner panel (not integral to the Backup Gateway), OR just connect the 30 amp breaker for each battery directly onto the backup loads panel?

 

[jaggedben]

Is another option to use a stand-alone combiner panel (not integral to the Backup Gateway), OR just connect the 30 amp breaker for each battery directly onto the backup loads panel?

Yes.

 

[Grouch1980]

Thank you both.

 

[wwhitney]

Is another option to use a stand-alone combiner panel (not integral to the Backup Gateway), OR just connect the 30 amp breaker for each battery directly onto the backup loads panel?

Certainly a stand-alone combiner panel is fine.

If you put the generation breakers in the backup loads panel, then you have to pay attention to the rules on not overloading the busbar. E.g. with a 200A busbar, and (2) 30A Powerwall breakers, and a 40A PV breaker for a 32A inverter, the generation adds up to 100A (after the 125% factor), so under the 120% rule you could only supply the panel with a 140A breaker (which doesn't exist, so round down to 125A).

The advantage of the H topology with the service as just a single breaker is that it avoids needing to apply the busbar rules. All the interconnection is done via the H feeder, and the two loads panels just need main breakers to comply with the feeder interconnection rules.

Cheers, Wayne

 

[Grouch1980]

If you put the generation breakers in the backup loads panel, then you have to pay attention to the rules on not overloading the busbar. E.g. with a 200A busbar, and (2) 30A Powerwall breakers, and a 40A PV breaker for a 32A inverter, the generation adds up to 100A (after the 125% factor), so under the 120% rule you could only supply the panel with a 140A breaker (which doesn't exist, so round down to 125A).

Actually I'm glad you brought this up, I did have this question as well. is this for the 2008 NEC version? Because in the 2017 NEC, it mentions the 120% rule for no more than 2 sources, one being your main utility source and the other "another power source". For multiple / more than 2 sources (which we would have in this case of multiple 30 amp battery breakers, the PV array, and the utility source), the 2017 NEC just says you can't exceed 100% of the busbar. Do i have this correct or no? Assuming everything is connected to the backup loads panel.

 

[wwhitney]

None of my comments are specific to the 2008 NEC, that's a very old version in use in only a few areas.

While 2017 705.12(B)(2)(3)(b) starts off with "where two sources . . ." I think it is common to treat any number of breakers together at the end of the busbar opposite the grid connection as a single source. Certainly the physics is the same. You could have a separate combiner panel, with just a single feeder to a single breaker, and in terms of busbar currents it would be the same as putting multiple breakers together at the end of the busbar.

Cheers, Wayne

 

[Grouch1980]

None of my comments are specific to the 2008 NEC, that's a very old version in use in only a few areas.

Welcome to the wonderful world of NYC

 

[LarryFine]

I tried looking online for wiring diagrams of multiple Tesla Powerwall 2's connected in parallel, but could only find installation pics, not actual wiring diagrams, such as the following:

2. How is the output wiring of each battery interconnected together? I doubt they are just spliced together. How do they all connect to the backup loads panel?

Maybe there are separate conductors to the panels in the conduits.

 

[Grouch1980]

Maybe there are separate conductors to the panels in the conduits.

Yeah I gathered that from here. I just wasn't sure if they go to separate breakers or not.

 

[LarryFine]

Yeah I gathered that from here. I just wasn't sure if they go to separate breakers or not.

That is what I meant to suggest; separate breakers.

 

[Grouch1980]

That is what I meant to suggest; separate breakers.

got it.

 

[ggunn]

Actually I'm glad you brought this up, I did have this question as well. is this for the 2008 NEC version? Because in the 2017 NEC, it mentions the 120% rule for no more than 2 sources, one being your main utility source and the other "another power source". For multiple / more than 2 sources (which we would have in this case of multiple 30 amp battery breakers, the PV array, and the utility source), the 2017 NEC just says you can't exceed 100% of the busbar. Do i have this correct or no? Assuming everything is connected to the backup loads panel.

Those are two different ways of qualifying a busbar. In the 2017 NEC the "120% rule" is 705.12(B)(2)(3)(b). Your comment I highlighted refers to 705.12(B)(2)(3)(c), and it's what we generally use for designing AC combiner and generation panels.

 

[Grouch1980]

If you have a home that has a 3 phase service... 120/208 volts, 3 phase, 4 wire... does Tesla offer a 3 phase battery? if not, would it be possible to connect multiple Powerwall 2's, which are single phase, onto a 3 phase combiner panel, where one battery connects to phase A and B, the other to B and C, and so on? I would imagine not.

 

[jaggedben]

As far as I know Tesla doesn't offer that. They offer 3-phase in their commercial products but those packs are much bigger than 3 Powerwall 2s.

Per another thread today, Generac has a solution (formerly Pika) that is a 3-phase inverter of a residential size.

I think I've only ever seen one residential property with a 3-phase service.

 

[Grouch1980]

As far as I know Tesla doesn't offer that. They offer 3-phase in their commercial products but those packs are much bigger than 3 Powerwall 2s.

Per another thread today, Generac has a solution (formerly Pika) that is a 3-phase inverter of a residential size.

I think I've only ever seen one residential property with a 3-phase service.

Thanks, I'll look thru that thread. In NYC there's apartments here and there with 3 phase power... in the same building with other apartments that are single phase. And a stand-alone house actually that's being built with 3 phase, in Brooklyn. It's sporadic.

 

[Grouch1980]

NYC doesn't allow batteries inside a home... per the FDNY. So that stand-alone house wouldn't be able to get a battery anyway. it is getting a solar PV array on its rooftop however. I'm not sure though if the FDNY lets you place the battery outside the house. I'd have to check.