Powerwall 2 into Sub-Panel?

[njmurvin]

I am researching a project to install 2 Powerwall 2s into an existing solar installation on my house. When I had my solar system installed a couple of years ago (27 LG 370 panels with IQ7 microinverters), there were complications surrounding the routing of conduit and placement of the combiner box, etc. near my main panel due to a fireplace and other obstructions. Since I had a 200 amp sub-panel located on the opposite side of the house with plenty of clearance, it was decided to run the solar to the sub-panel instead of the main panel.

I am wondering how this setup might complicate my ability to fully utilize an energy storage system such as the Powerwall. Part of my confusion is due to a lack of in-depth understanding of how the Powerwall works with regard to its interaction with the Gateway, etc.

My primary objective for the battery system is to optimize my electric usage. I live in SCE territory and am on a TOU plan. I want to be able to store energy during lower cost hours to use during the expensive peak hours. Since we don't have that many power outages where I live, having backup is a secondary priority - but would certainly be nice to have. I would prefer to energize the whole house during backup operation. So, I don't believe a backup loads panel will be necessary.

1) Has anyone installed a Powerwall to a sub-panel at some distance from their main panel? If so, what were the challenges/sacrifices for such an installation? I am assuming the Powerwalls need to be placed near where the solar panel outputs come together (in my case, the combiner box).

2) What exactly does the Gateway do and how does it do it?

3) How is the Gateway connected to the Powerwalls? Can this be a wireless connection? If not, what kind of wire would I have to run between the Gateway and the Powerwalls?

Sorry for the long-winded post.

 

[Gwgan]

Everything connects to the Gateway. The Gateway sits between the mains and the whole house, including the batteries, main panel, and subpanel loads. The service main moves from the main panel to the Gateway so the Gateway will need to be near where power comes into the building. The Powewall 2s connect to the Gateway so they need to be nearby as well. The solar feed will have to move from the subpanel to the Gateway. Not an electrician here, but could the line path between main and subpanel be used to bring the solar feed near the Gateway via the main panel box (pass though, not connected inside main panel)? My whole-house install included the addition of an unused subpanel for “potential future non-backed-up loads” so you may need to add a subpanel even if you have a whole-house plan.

 

[Gwgan]

PW can be up to 150 feet from the Gateway but you still need to feed the solar directly to the Gateway instead of any existing panel.

Powerwall Installation Resources for Installers | Tesla Support

Learn about the installation process for Powerwall and the different components of a Powerwall system, including Backup Gateway 2 and Backup Switch.

www.tesla.com

correction: see miimura below, the solar generation does not have to connect directly to the Gateway but then a remote meter must be installed. If the remote meter and Gateway are too far apart for wireless communication then a wired connection up to 164 feet can be used.

 

[miimura]

If there is a good place to install the Gateway and Powerwalls near the utility meter, then the solar can be measured with a remote Neurio meter without relocating the solar circuits.

 

[njmurvin]

Thanks for your response. This was my original thinking, but when I saw that there was a separate gateway, I had hoped there might be a way to keep the PWs remote from the gateway.

... Not an electrician here, but could the line path between main and subpanel be used to bring the solar feed near the Gateway via the main panel box (pass though, not connected inside main panel)?

This is an interesting idea. I don't know enough about the functionality of the GW to know the ramifications. The sub-panel end of that line path has to stay connected to the sub-panel loads. Otherwise, there's no way to get power to those loads. I'm guessing that would reduce the power coming from the solar feed by whatever those loads are pulling. That could range from minimal effect to completely killing the solar feed (if both AC units are on). This would be rare. So, I could probably live with that. My bigger concern is how the GW would enable power to get back to my sub-panel. That would only happen when the grid and/or battery are connected to the solar feed since the solar feed is the line path back to the sub-panel. I wonder if this connection would be made ONLY when the GW is exporting solar power to the grid?

If I treat the 175 amp feed to my 200 amp sub-panel as the service main (for PW purposes) and locate the GW at my sub-panel location (where the solar already is), it should work but I would only be able to power the loads in my sub-panel during an outage. Since my main objective is load shifting, I could probably live with this. Do you see any problems doing it this way?

 

[njmurvin]

If there is a good place to install the Gateway and Powerwalls near the utility meter, then the solar can be measured with a remote Neurio meter without relocating the solar circuits.

Thank you. Yes. I believe there should be room near the main panel. Wireless would be great. I'm pretty sure it's less than 164' if it won't work. There's so much I don't know about how these components work together.

 

[Gwgan]

The Gateway is just a smart switch between the service grid and your own microgrid which shuts off the connection between the two when the batteries are the source of power. It uses the solar feed and your TOU settings to know when to flip the switch and can respond to loss of grid power. The remote meter on the solar feed seems like the simplest way to keep your whole house on one side of the Gateway and not have to move the solar tire in.

 

[Fruitcake]

The Gateway is just a smart switch between the service grid and your own microgrid which shuts off the connection between the two when the batteries are the source of power. It uses the solar feed and your TOU settings to know when to flip the switch and can respond to loss of grid power. The remote meter on the solar feed seems like the simplest way to keep your whole house on one side of the Gateway and not have to move the solar tire in.

It does a lot more than that! As I learned the hard way. (e.g. When the Gateway fails hard and requires onsite repair. Which takes forever due to Tesla's pitiful customer care. But I digress.....)

The Gateway is also responsible for telling your Powerwalls when to charge, and exactly by how much to charge. It does this by measuring your solar output (say, 2kW), subtracting your home's energy consumption if any (say, 0.8kW), and the difference (1.2kW) becomes how much your Powerwall is allowed to charge. How frequently the Gateway updates this data, I do not know. I am guessing 1Hz.

Why this limitation? Apparently, you can thank the intersection of our wonderful electric utilities and America's eccentric tax codes, which stipulate that to obtain the tax breaks for solar installations (currently in the range of ~25%) home batteries may ONLY charge from solar production.

The EXCEPTION to this rule are emergency warning systems akin to Tesla's "Storm Watch" mode. For example, If the National Weather Service declares an imminent weather condition for your area (say a hurricane) the Powerwalls will bypass the above artificial restriction, and charge from the grid as rapidly as they can. I have personally seen this Storm Watch mode in operation, though I will say it seems random - it sometimes activates when I least expect it, and then it DOESN'T activate even when the local news says we're about to get pounded with some exotic derecho or nor'easter or whatever. Once again, it is the Gateway that directs the Powerwall to behave in this manner.

And why (I hope) you understand by now, why a malfunctioning Gateway can have such deleterious effects on your Powerwalls and how they work (or don't).

Fruicake

 

[jjrandorin]

My primary objective for the battery system is to optimize my electric usage. I live in SCE territory and am on a TOU plan. I want to be able to store energy during lower cost hours to use during the expensive peak hours.

As long as by "store energy during low cost hours" you mean "Store energy I generate with solar" then you can do that. If you mean "charge from the grid during off peak to discharge into my home during Peak, you will not be able to do that, with powerwalls, in the US, if you have solar (which is most people in the US who are buying powerwalls or contemplating that).

I am also reasonably certain that you will not be able to purchase powerwalls without solar from tesla directly at all right now, so if this is something you are interested in, you will need to investigate purchasing through a third party solar installer, not tesla.

Perhaps you know both of the things above, but sometimes people dont know that they will not be able to "charge from the grid off peak and use that energy during peak time", and thats what it sounded like you were thinking you were going to be able to do.

 

[Gwgan]

It does a lot more than that!

Yes, I shouldn’t have said “just” a switch but it is a useful simplification when considering system layout.

 

[njmurvin]

As long as by "store energy during low cost hours" you mean "Store energy I generate with solar" then you can do that. If you mean "charge from the grid during off peak to discharge into my home during Peak, you will not be able to do that, with powerwalls, in the US, if you have solar (which is most people in the US who are buying powerwalls or contemplating that).

I am also reasonably certain that you will not be able to purchase powerwalls without solar from tesla directly at all right now, so if this is something you are interested in, you will need to investigate purchasing through a third party solar installer, not tesla.

Perhaps you know both of the things above, but sometimes people dont know that they will not be able to "charge from the grid off peak and use that energy during peak time", and thats what it sounded like you were thinking you were going to be able to do.

I have to admit that when I first began to explore PWs, I thought that I would be able to benefit from both excess solar generation and TOU's super off peak hours to "top off" my batteries. Reality came crashing down as I read about these limitations. So, yes, I am painfully aware.

Regarding the sale of unbundled PWs, I was actually surprised when I was told I COULD buy the PWs (from LA Solar Group). Even so, they don't project availability until next summer. I am not ruling out going in another direction at some point before they become available.

 

[jblazar]

I have to admit that when I first began to explore PWs, I thought that I would be able to benefit from both excess solar generation and TOU's super off peak hours to "top off" my batteries. Reality came crashing down as I read about these limitations. So, yes, I am painfully aware.

Regarding the sale of unbundled PWs, I was actually surprised when I was told I COULD buy the PWs (from LA Solar Group). Even so, they don't project availability until next summer. I am not ruling out going in another direction at some point before they become available.

My experience with LA Solar has been absolutely terrible. I would not recommend that company to my worst enemy (well, maybe I would).

 

[ptdusn]

I have to admit that when I first began to explore PWs, I thought that I would be able to benefit from both excess solar generation and TOU's super off peak hours to "top off" my batteries. Reality came crashing down as I read about these limitations. So, yes, I am painfully aware.

Regarding the sale of unbundled PWs, I was actually surprised when I was told I COULD buy the PWs (from LA Solar Group). Even so, they don't project availability until next summer. I am not ruling out going in another direction at some point before they become available.

I would recommend, (if not too late), going with Sunrun. They have PWs available and should be able to install them without you having to add more PVs.