(powerwall) gateway question

fritter63

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So, looks like PG&E is forcing us to become grid agnostic. Been doing my research on the Powerwall, actually looks almost free with the tax incentives.

I tried contacting Tesla through their request form on Powerwall, all I got was an attempt to sell me solar, then a link to the reservation page for Powerwall. They don't seem to be willing to answer my questions ahead of reservation.

So I thought I'd try asking here first. Attached is a diagram of our rather complicated power system.

Questions:
  • Does the gateway need to be co-located with the Powerwalls to communicate with them and perform the switchover when the grid goes down?
    • Ie, can I locate it out at the main panel, with the Powerwalls located in the garage?
  • If not, how does it communicate (if at all) with Powerwall?
  • Because all our sub panels are connected through the main, can the Powerwalls (s) be located anywhere and still power both houses?
  • Does the gateway itself need an internet connection? Right at the point of installation?
  • Is there email at Tesla I can use to try to get these questions answered?
  • Bonus question: How does the Powerwall enable my inverters which are normally shutoff when the grid is down? Does the battery itself provide enough input to make the inverters think that the grid is up?
Thanks for any help.

Blank Diagram.jpeg
 

kjtesla

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Contact Brad: He is a realtor that did an hour long segment on KMJ this weekend on this specific subject. I'm sure he has your answer!

Brad Maaske
VISALIA, CA
 

JasonF

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I'm not certain about how the Powerwall switches from grid to solar to battery, but here are a few general rules it most likely has to follow:

- When the grid power goes out, neither the batteries nor solar are allowed to feed power back into the outside grid.

- Most likely (from your diagram) the "gateway" is responsible for closing off the outside grid when the house is entirely on battery power, or whenever the outside grid goes down.

- Once the outside grid is disconnected, the solar and batteries can be connected to any sub-panel, as long as the wiring run between subpanels can handle the number of amps both can supply at once. You have to assume it's possible they could both be feeding in at once - not to mention the batteries could be charging off that same amperage. For instance, if the Powerwall can supply 100 amps, and the Solar can also supply 100 amps, they either both have to be attached to 100 amp subpanels, or both to a 200 amp subpanel. You probably can't connect both to a 100 amp subpanel.

- The batteries will probably activate the solar inverters, unless the batteries are isolated from the solar system somehow. There might be an issue with that if the Powerwall hasn't been told the power its receiving is from solar and not the grid - it might shut off and start charging, and then the solar panels would shut down, etc. That's an issue to bring up with your installer.

There might be an error in your diagram where you have two 220 volt EV chargers connected to a 100 amp subpanel along with Powerwalls. If all 3 are charging at the same time, you'll be over the limit for that subpanel, and the main breaker for it will probably trip.
 

fritter63

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There might be an error in your diagram where you have two 220 volt EV chargers connected to a 100 amp subpanel along with Powerwalls. If all 3 are charging at the same time, you'll be over the limit for that subpanel, and the main breaker for it will probably trip.

Good point. Of course, we can always bump that circuit breaker up a little (within wire limitations). We ran pretty thick cable to that sub panel IIRC.

The good news is that the cars can only draw 32A each (for obvious reasons), but we typically charge them at 20 and 15 amps as that's "fast enough" to get the job done overnight. And we rarely charge them at the same time. So that would leave min 36 amps for the Powerwalls (need to figure out how the solar panels pushing back in at the same time would affect that).

I did find an installation manual online!

https://www.manualslib.com/manual/1435734/Tesla-Powerwall-2-Ac.html?page=13#manual

So if they're allowing down to 10 ga wire, then that's 30A I think?

There is is on page 38: "The Powerwall connection to the main electrical panel requires a 30 A circuit breaker
with a maximum short circuit current rating of 10 kA"

I'm guessing that's one breaker per Powerwall.

Note that that page also indicates a direct CAT-5 connection between the gateway and the Powerwall, (note to self, next time just put lots of extra conduit for expansions) so looks like I have no choice but to put the Powerwall out at the main panel (mounted on the back side of the backboard, facing EAST), and that's fine as that thing has a TON of unused circuit slots on it, and 400A capacity.

Maybe I'll build a little shade roof for it. :)

And I still have to solve wireless router issue.
 

JasonF

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The good news is that the cars can only draw 32A each (for obvious reasons), but we typically charge them at 20 and 15 amps as that's "fast enough" to get the job done overnight. And we rarely charge them at the same time. So that would leave min 36 amps for the Powerwalls (need to figure out how the solar panels pushing back in at the same time would affect that).

It's going to be close. 32 + 32 + 30 = 94, which is above the continuous load recommended for a 100 amp panel.


Note that that page also indicates a direct CAT-5 connection between the gateway and the Powerwall, (note to self, next time just put lots of extra conduit for expansions) so looks like I have no choice but to put the Powerwall out at the main panel (mounted on the back side of the backboard, facing EAST), and that's fine as that thing has a TON of unused circuit slots on it, and 400A capacity.

You can still have it in the garage, it just depends how much wiring you're willing to do. You can get a large roll of CAT-5 cable and run it through the attic. It's low voltage, so it doesn't require anything special besides holes big enough at each end.
 

fritter63

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You can still have it in the garage, it just depends how much wiring you're willing to do. You can get a large roll of CAT-5 cable and run it through the attic. It's low voltage, so it doesn't require anything special besides holes big enough at each end.

The main panel is physical separated from the house, at least 80 feet, across a lot of landscaping and pavement.
 

DrSmile

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So, looks like PG&E is forcing us to become grid agnostic. Been doing my research on the Powerwall, actually looks almost free with the tax incentives.

I tried contacting Tesla through their request form on Powerwall, all I got was an attempt to sell me solar, then a link to the reservation page for Powerwall. They don't seem to be willing to answer my questions ahead of reservation.

So I thought I'd try asking here first. Attached is a diagram of our rather complicated power system.

Questions:
  • Does the gateway need to be co-located with the Powerwalls to communicate with them and perform the switchover when the grid goes down?
    • Ie, can I locate it out at the main panel, with the Powerwalls located in the garage?
  • If not, how does it communicate (if at all) with Powerwall?
  • Because all our sub panels are connected through the main, can the Powerwalls (s) be located anywhere and still power both houses?
  • Does the gateway itself need an internet connection? Right at the point of installation?
  • Is there email at Tesla I can use to try to get these questions answered?
  • Bonus question: How does the Powerwall enable my inverters which are normally shutoff when the grid is down? Does the battery itself provide enough input to make the inverters think that the grid is up?
Thanks for any help.

View attachment 30019

Some of these answers depend on the version of Gateway and how many Powerwalls you have and how it's set up. But assuming you have at least 2 Powerwalls and have whole house backup:

1) My gateway is outside and the Powerwalls are inside, connected through conduit about 50 feet away. So no they don't need to be co-located. The gateway itself has a breaker to take the system off-grid
2) If your main panel is backed up directly without any subpanel in between like mine anything after the main panel will be powered (within the 7KW per PW limit)
3) The gateway is wireless capable. I access it through my home WiFi
4) The gateway raises the frequency of the supplied current to a level that turns off the inverter and takes the solar offline once the Powerwall charges to full. Once the PW drops to ~93% charge the frequency will drop and the solar system will turn back on (after a restart timeout). As long as you are making excess solar the system will cycle on and off in this range.The frequency had to be adjusted for my house in order not to interfere with the A/C soft starts and the Computer UPS devices. This took a long time (months).

Once set up correctly the system works amazingly well.
 

fritter63

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4) The gateway raises the frequency of the supplied current to a level that turns off the inverter and takes the solar offline once the Powerwall charges to full. Once the PW drops to ~93% charge the frequency will drop and the solar system will turn back on (after a restart timeout). As long as you are making excess solar the system will cycle on and off in this range.The frequency had to be adjusted for my house in order not to interfere with the A/C soft starts and the Computer UPS devices. This took a long time (months).
.

Well, hopefully that's just your system. I want my solar panels to keep outputting and turn the meter backwards if the PW is charged.

Reserved last night, and got my first contact email today, we'll just have to see what they say.

Thanks all for the help.
 

DrSmile

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Well, hopefully that's just your system. I want my solar panels to keep outputting and turn the meter backwards if the PW is charged.

Reserved last night, and got my first contact email today, we'll just have to see what they say.

Thanks all for the help.

That was in regards to the last question, ie when the system is off grid. You can not produce solar once the Powerwalls are full when off grid.
 

GenSao

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So, looks like PG&E is forcing us to become grid agnostic. Been doing my research on the Powerwall, actually looks almost free with the tax incentives.

I tried contacting Tesla through their request form on Powerwall, all I got was an attempt to sell me solar, then a link to the reservation page for Powerwall. They don't seem to be willing to answer my questions ahead of reservation.

So I thought I'd try asking here first. Attached is a diagram of our rather complicated power system.

Questions:
  • Does the gateway need to be co-located with the Powerwalls to communicate with them and perform the switchover when the grid goes down?
    • Ie, can I locate it out at the main panel, with the Powerwalls located in the garage?
  • If not, how does it communicate (if at all) with Powerwall?
  • Because all our sub panels are connected through the main, can the Powerwalls (s) be located anywhere and still power both houses?
  • Does the gateway itself need an internet connection? Right at the point of installation?
  • Is there email at Tesla I can use to try to get these questions answered?
  • Bonus question: How does the Powerwall enable my inverters which are normally shutoff when the grid is down? Does the battery itself provide enough input to make the inverters think that the grid is up?
Thanks for any help.

View attachment 30019

The Powerwall Gateway is limited to 200 A of pass-though power. In your case, you'll likely need TWO Powerwall Gateways: 1) between the main panel at the street and the house sub-panel and 2) between the main panel at the street and the granny unit sub-panel. Effectively you will have two separate systems.

Each gateway should be physically placed near the house sub-panel and granny unit sub-panel. I imagine you will want to have two powerwalls for each gateway for a minimum of four Powerwalls. Powerwall can be placed anywhere, though Tesla prefers the solar breakers and 30 A Powerwall breakers to be physically close to each other. A constraint is the a physical data cable connecting the Powerwalls to the Gateway.

Depending on placement and total number of the Powerwalls, due to the 120% rule (NEC 705.12(D)(2)), you may be forced to upsize your Solar sub-panels. Also to comply with the NEC, you may be forced to either derate the breakers to the main panel at the street or upsize the busbar of house sub-panel and granny unit sub-panel. See my below layout for example.

three-line-diagram.jpg




Tesla went with derating the breaker to 150A.
Power loads: 150 A + 25 A + 30 A + 30 A = 235 A
Allowable busbar ampacity = 200 A x 1.20% = 240 A
235 A < 240 A, OK!

A better option would be a 225 A load center.
Power loads: 175 A + 25 A + 30 A + 30 A = 260 A <
Allowable busbar ampacity = 225 A x 1.20% = 270 A
260 A < 270 A, OK!
 

fritter63

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Good info, thanks @GenSao .

Waiting to hear from an installer who has SGIP credits left, but not optimistic. I contacted one (well known name) and found that their "side by side" cost comparison to Tesla simply shows that they are keeping the SGIP rebate themselves (they pad the total cost for the exact same amount).

So there is no reason not go with Tesla (as a stockholder!) and it will cost more than we thought. Yeah, I know Tesla will still get the hardware money, but I don't like the idea of installers getting the rebate (tax money). And yes, I'm aware that Tesla kinda did similar with the cars.