Powerwall Connection Options

[power.saver]

I'm getting my site survey this week, and have been planning the PowerWall install for a little while now. I'm interested in getting any feedback on my system as it relates to how the PowerWalls are connected.

Some background info. I have an existing 5.13kW solar system, and TOU metering (SCE). My primary goal is for load shifting (self-powered mode) and backup for outages, which are rare. I have one big load, an AC unit that would probably exceed the capacity of 2 PowerWalls.

My question relates specifically to the AC unit. If it is outside the gateway, separate from the house backed-up loads, and I use it during TOU peak periods but I'm not generating enough solar to cover it, I suspect the PW will not discharge as it can't see that load. If I bring it inside the gateway so the load is seen, it would appear I need 3 PWs to cover worse-case backup loads.

Am I correct on these assumptions? Certainly I plan to ask them during the Tesla site survey, but would appreciate any comments or feedback on this situation.

Attached are schematics of my existing panels, and proposed configurations with either 2 or 3 PWs.

Thanks.

 

[wwhitney]

Tesla's rule of thumb is that the maximum backed up breaker size is 30A per Powerwall, so 60A for (2) Powerwalls. Why do you think that (2) Powerwalls can't back up your AC that's on a 50A breaker?

Cheers, Wayne

 

[power.saver]

Wayne,

I was not sure of that. Thinking that the sub-panel is currently on a 100A breaker, the total load with the AC on might exceed 60A.

Certainly if 2 PW would be sufficient then I will go with that option. Thanks for your input!

 

[wwhitney]

Well, I can't say how Tesla applies its 30A per Powerwall rule of thumb, but the only rational way to do it would be to look only at the branch circuit breakers and ignore the feeder breakers. Not sure if Tesla ever does an overall load calculation or just goes by the rule of thumb.

BTW, what is the bus rating of your existing panel with the 30A solar breaker and 100A feeder breaker? I assume it is at least 125A. If you want to add two 30A Powerwall breakers to that panel, that will only work if the bus is rated at least 150A.

Cheers, Wayne

 

[power.saver]

Wayne,

It is a 125A bus panel. I kind of figured that would need to be replaced, but didn't draw it as new until I knew for sure.

 

[miimura]

I'm guessing this would be how it would be installed with one or two PWs. The Gateway has two output terminals, so one can go directly to your existing sub-panel and one would go to a new "Generation Panel". A third CT can be added in with the "Grid" CTs to measure and offset your AC use even though it would not be backed up. Another user on the forum had his system installed this way.

 

[power.saver]

miimura,

Wow, thanks for taking the time to show that on my drawing. I wasn't aware of the 3rd CT option... that would be really useful.

It's hard to find specific information on all this equipment. Appreciate your insights.

 

[GenSao]

Another layout to consider is to have the gateway directly between the meter and your existing electrical panel. As Miimaru stated, "The Gateway has two output terminals". But instead, I would consider running one to a re-purposed generation panel and one to your existing home loads panel. The biggest assumption (an unknown to us online) is the physical arrangement of your electrical equipment and if there is room.

Since your AC is on a 50A breaker, you can include your AC as part of the whole home backup with 2X Powerwalls (30A x 2 = 60A). If there is not enough solar to run the AC, the Powerwalls will supplement the difference with stored energy. In the event of a power outage, I believe you can manage your loads within the 60A (10 kW) allowance.

 

[NuShrike]

Look around in my thread asking similar: Is there a electrical reason for two+ PowerWall 2s vs PV system size?

Summary, get the LRA of your A/C. Make sure it's under 60A. If not, see if it's soft-starter compatible.

I'm surprised your installer isn't offering a soft-starter install instead of upselling you to 3 PWs. Rebate reasons?

 

[power.saver]

GenSao,

Thanks for this other option. It would simplify wiring by not changing the run to the sub panel. That would be a big plus.

There is plenty of space on the wall with the meter panel, inverter and existing gen panel to add all the equipment.

NuShrike,

I will read your thread. I was looking for more information on this, so that will be interesting. The LRA of the A/C is 129A, well above 60A. I don't know if it is soft-start compatible, that is something I was going to ask during the site survey.

The installer comes this week... and I only "reserved" one PW, but over the phone the Tesla rep said I probably need two. I want to have as much information from folks like you who have done this so I can ask the right questions when they are here.

Thanks!

 

[wwhitney]

Another layout to consider is to have the gateway directly between the meter and your existing electrical panel. As Miimaru stated, "The Gateway has two output terminals". But instead, I would consider running one to a re-purposed generation panel and one to your existing home loads panel.

FYI, when using the double lugs on the load side of the Gateway in this way, you are connecting an alternate power source to the middle of a feeder, namely the feeder from the utility disconnect to the loads panel. This requires the loads panel to have a main breaker in it, unless you want to upgrade the portion of the feeder from the Gateway to the loads panel to have a capacity equal to the sum of the utility disconnect breaker and (approximately) the alternate power source breakers. See 2016 California Electrical Code 705.12(D)(2)(1).

Cheers, Wayne

 

[power.saver]

I had my site survey done today. The rep was a Telsa employee, not SolarCity. He took a lot of photos and measurements of the house, but couldn't answer any of my questions about the AC load. I did show him the drawings and he took pictures of them.

One question he asked was "What is on the other side of the wall?" where I want to mount the PW. It's a bathroom, and he seemed fine with that. But now thinking about that question, is it due to noise from the PW? For those who have them can you tell me if there is any appreciable or noticeable noise coming from them?

Thanks.

 

[TomDiego]

One question he asked was "What is on the other side of the wall?" where I want to mount the PW. It's a bathroom, and he seemed fine with that. But now thinking about that question, is it due to noise from the PW? For those who have them can you tell me if there is any appreciable or noticeable noise coming from them?.

My PWs are mounted inside the garage on an outside wall. If I go out into the garage, there is a soft hum that I can hear from the doorway about six feet away. The cooling system is at the top of the unit, with the air intake at the upper left side and the air exhaust at the upper right side. Even standing right next to them the hum is pretty innocuous. I don't know whether there would be any vibration that would be noticeable on an inside wall and I doubt that the sound would go through an exterior wall.

 

[power.saver]

Thanks TomDiego. That's about the level of sound from my SMA inverters and they are mounted on the outside of the bedroom wall and haven't been a problem.

 

[Shygar]

FYI, I had my backup gateway only back up my main house subpanel. My Tesla Wall Connector and AC are outside of the backup gateway. However, I found out that my Tesla Wall Connector still draws from my powerwall even though it's not being backed up by it. I had some issues with my Neurio so maybe that plays a bigger part than I thought and it doesn't behave like that anymore, but I was surprised that it was drawing from the battery like it would if I had solar at the time (this was at night the one time I tested it).

 

[power.saver]

Shygar,

I saw your other thread, and was intrigued at what happened. That's actually what I want to do with my A/C, namely have the PW supply part or all of it when the grid is up and offset the usage, but not require it be backed up since the load is too much for 1 PW. I think it can be done with the right CT placement. But the site surveyor and my rep don't seem to understand this. Hopefully the designer does, at least that where it is now.

 

[miimura]

FYI, I had my backup gateway only back up my main house subpanel. My Tesla Wall Connector and AC are outside of the backup gateway. However, I found out that my Tesla Wall Connector still draws from my powerwall even though it's not being backed up by it. I had some issues with my Neurio so maybe that plays a bigger part than I thought and it doesn't behave like that anymore, but I was surprised that it was drawing from the battery like it would if I had solar at the time (this was at night the one time I tested it).

If the Neurio can see the power consumption, the Gateway will tell the Powerwall to offset it, even if it is outside the Gateway. My setup currently does not see my EVSEs, so the Powerwall makes no attempt to supply their energy. Until the TOU settings are implemented, it's better that way. However, I would definitely want my AC to be offset with the Powerwall, if I had it installed.

@Shygar was the user I was thinking of when I marked up the diagram for @power.saver upthread.

 

[power.saver]

miimura,

I gave a copy of your drawing, and he others, plus one I made, showing all these options, but the site survey didn't seem to know much. I've since learned this is possible, and want to do just as you suggest. I'll wait and see what the designer comes back with.

 

[miimura]

miimura,

I gave a copy of your drawing, and he others, plus one I made, showing all these options, but the site survey didn't seem to know much. I've since learned this is possible, and want to do just as you suggest. I'll wait and see what the designer comes back with.

Yeah, I found the site survey guys are just there to collect the data - take measurements, take pictures, and write down what all is connected to your existing electrical panels. I think even the permit plans were really unclear and nobody I talked to knew anything about the technical details of the install until the guys showed up to actually do the install.

 

[Shygar]

If the Neurio can see the power consumption, the Gateway will tell the Powerwall to offset it, even if it is outside the Gateway. My setup currently does not see my EVSEs, so the Powerwall makes no attempt to supply their energy. Until the TOU settings are implemented, it's better that way. However, I would definitely want my AC to be offset with the Powerwall, if I had it installed.

@Shygar was the user I was thinking of when I marked up the diagram for @power.saver upthread.

So I can confirm this. After moving the Neurio's to monitor the power draw from my wall connector, it is now drawing from the battery, even though my battery and AC are not in my backup gateway.

I have a 60 amp wall connector, so i'm drawing at the full 48 amps that a Model 3 can charge at. So that's 11 kWh. I can see it's drawing the full 5.0 kW from my battery and the remainder from the grid (since I charge at night).