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Just had 9.8kw Solar+2PW installed, have some noob questions.

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Hi folks,

I'm very late to the party due to moving twice in 3 years. But we're finally in a house that can support plenty of solar without any shade and we're not moving for a long, long time.

I've been spending all day reading this forum. Lots of great info.

We have a new 23x425w PV system on all four sides of our house, plus a PW+ and a Founders PW2 and Tesla Gateway (both referral awards, woot!)
There are four strings for each face of the house, and the largest string faces south (luckily)!

Since we have three A/C units and a hot-tub, I requested that we have a partial-house backup instead of whole-house, and Tesla was able to do that for us.
Why? Mainly because if we have a powercut and we're not home, I didn't want the A/C and hot tub to drain the PWs before we could shut them down. I want maximum backup battery time.

You can see two service panels in the second photo, the left panel is the non-essential loads and the right panel is the essential (backed-up) loads.
The system is working great so far (it's only been two somewhat cloudy days).

My first two questions are:
1. Obviously the 2 PWs only backup the essential loads panel. But what about solar generation? Will the solar energy supply both panels, or just the essential loads? I'm trying to wrack my brain to figure out the power flow, but I can't quite figure it out. For instance, say the PV is generating 8kW and the PWs are full. The essential loads (EL) are pulling 2kW and the non-essential loads (NEL) are pulling 4kW, so 6kW total demand, leaving 2kW left over. What gets sent back to the grid -- 2kW (8PV -2 EL -4 NEL) or 6kW (8PV - 2EL)? If only the essential loads gets the solar and 6kW is sent to the grid, wouldn't that energy just essentially "turn around" and power the NEL panel? I'm trying to figure out how this works.

2. See the third image below from the phenomenal Powerwall_Dashboard docker app. How do I fix the Y axis on the top chart? I've tried changing the Y axis to say 10kw, but that messes up the sun dashed line. I can't get it to look like all the other well-formatted graphs I see.

I'm sure I'll have many more questions as I get familiar with all of this. I don't yet have PTO, but I'm seeing some real strange data in the Tesla app, but I'll explain that in a follow-up post.

Thanks.



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1. Obviously the 2 PWs only backup the essential loads panel. But what about solar generation? Will the solar energy supply both panels, or just the essential loads? I'm trying to wrack my brain to figure out the power flow, but I can't quite figure it out. For instance, say the PV is generating 8kW and the PWs are full. The essential loads (EL) are pulling 2kW and the non-essential loads (NEL) are pulling 4kW, so 6kW total demand, leaving 2kW left over. What gets sent back to the grid -- 2kW (8PV -2 EL -4 NEL) or 6kW (8PV - 2EL)? If only the essential loads gets the solar and 6kW is sent to the grid, wouldn't that energy just essentially "turn around" and power the NEL panel? I'm trying to figure out how this works.
Solar supplies both panels. 2kW will go back to the grid in you example. However, prior to PTO, your system might not export at all (solar generation is reduced to match home load).
 
Your solar energy will naturally supply all loads and only the total surplus will go through your utility meter to the grid. However, there is a finer point that you need to be aware of: When the Powerwalls are supporting your loads, like in Time Based Control or Self Powered Mode, they can only offset the loads that are measured. By default, only the Backup loads are measured by the Gateway. If you want your Powerwalls to offset the usage of your NELs, there needs to be CTs installed on the grid feed closer to the meter than the Gateway.
 
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f you want your Powerwalls to offset the usage of your NELs, there needs to be CTs installed on the grid feed closer to the meter than the Gateway.

Thank you.

The Tesla crew did install two CTs and a transmitter in the NEL panel to send the total demand back to the gateway, so I think that's covered! (these CTs actually capture the total demand of both panels, they are on the main 200a feeds into the NEL panel).

So you're saying when the PWs are discharging, they might cover the NEL demand? But in a powercut situation, they won't? Just trying to understand the nuances here.

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Its definitely possible for "the system" to provide power to both the backed up, and non backed up loads, when grid connected, and still only provide power to the backed up loads when off grid.

I am not sure on a technical level how its wired (some of the more technical members here might be able to tell you) but I know it has to do with if the non backed up loads panel has CTs measuring those loads.

I know 100% it can work that way, because mine is the way I just described above. I have a "backed up loads" panel that includes every load in my home, except for my tesla HPWC's. This means that in a power outage my Tesla wall connectors are not powered. During normal operation though, when I charge my car, it absolutely will use powerwall power to charge the car(s).

I think the CTs are the key, but I am not the most technical member here by a long shot, so if thats wrong someone will correct me.

Congratulations on the install btw!
 
I know 100% it can work that way, because mine is the way I just described above. I have a "backed up loads" panel that includes every load in my home, except for my tesla HPWC's. This means that in a power outage my Tesla wall connectors are not powered. During normal operation though, when I charge my car, it absolutely will use powerwall power to charge the car(s).

That's great to hear, thanks!
 
And here's my follow-up question. When I switch to "Time Based Control" and it's after 8pm (off peak), I see no solar and no powerwall usage. I'm pulling straight 100% from the grid, which I assume is correct since that's the cheapest energy source (TOU plan), and the PWs are being saved to discharge during the day tomorrow (on-peak). This seems totally normal:


But if I switch to "Self-Powered Mode" to use the PWs at night, I get this crazy behavior (one minute shown below).


I can't begin to understand what's going on here. And I don't have PTO yet, so I can't send energy back to the grid, and I don't have "Grid Charging" enabled either (it's currently locked out for me). So what's happening here?
 
By default, only the Backup loads are measured by the Gateway. If you want your Powerwalls to offset the usage of your NELs, there needs to be CTs installed on the grid feed closer to the meter than the Gateway.
The GW2 has connections for both backed up and non backed up loads and can monitor both with the main site CTs so a second set of CTs isn't always necessary. This is the way mine is wired.

I believe the non backed up loads connection in the GW2 is limited to 100A so if you have more than that you would need to wire them separately and add another set of CTs as you stated which looks like the case for the OP.
 
And here's my follow-up question. When I switch to "Time Based Control" and it's after 8pm (off peak), I see no solar and no powerwall usage. I'm pulling straight 100% from the grid, which I assume is correct since that's the cheapest energy source (TOU plan), and the PWs are being saved to discharge during the day tomorrow (on-peak). This seems totally normal:


But if I switch to "Self-Powered Mode" to use the PWs at night, I get this crazy behavior (one minute shown below).


I can't begin to understand what's going on here. And I don't have PTO yet, so I can't send energy back to the grid, and I don't have "Grid Charging" enabled either (it's currently locked out for me). So what's happening here?
Something is wrong with your system. Likely a misconfigured or backwards installed CT.
 
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The GW2 has connections for both backed up and non backed up loads and can monitor both with the main site CTs so a second set of CTs isn't always necessary. This is the way mine is wired.

I believe the non backed up loads connection in the GW2 is limited to 100A so if you have more than that you would need to wire them separately and add another set of CTs as you stated which looks like the case for the OP.
Yes, there are many ways to wire a Tesla Backup Gateway. The ability to measure all grid and pass through a non-backup feed to a sub-panel is one feature that the Gateway 2 has that the Gateway 1 does not. The ability to install an internal sub-panel bus inside the Gateway 2 is another.
 
The GW2 has connections for both backed up and non backed up loads and can monitor both with the main site CTs so a second set of CTs isn't always necessary. This is the way mine is wired.

Mine is not wired that way. I have the 200a main service directly into the NEL panel, not going through the GW first.

They then take a 100amp breaker off the NEL panel to feed the GW, and then a 100amp feed back to the EL panel.

The way you describe they typically have the main 200a feed from the meter go to the GW first, and then split off the EL and NEL loads. The problem is that my NEL loads are a lot more than 100amps (3 A/C compressors, 3 HVAC air handlers, a 60a hot-tub and a 50a oven)... so that's why it's done this way.
 
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Mine is not wired that way. I have the 200a main service directly into the NEL panel, not going through the GW first.

They then take a 100amp breaker off the NEL panel to feed the GW, and then a 100amp feed back to the EL panel.

The way you describe they typically have the main 200a feed from the meter go to the GW first, and then split off the EL and NEL loads. The problem is that my NEL loads are a lot more than 100amps (3 A/C compressors, 3 HVAC air handlers, a 60a hot-tub and a 50a oven)... so that's why it's done this way.
I was going to suggest turning off the NEL panel to try troubleshoot the issue but obviously based on how it's wired that's not going to work:D. Hope Tesla is able to resolve it next week.
 
Yes, there are many ways to wire a Tesla Backup Gateway. The ability to measure all grid and pass through a non-backup feed to a sub-panel is one feature that the Gateway 2 has that the Gateway 1 does not. The ability to install an internal sub-panel bus inside the Gateway 2 is another.
Yes I have both an internal (to the GW) backup sub panel and a separate external backup subpanel, although the internal panel is just combining the PWs and solar.
 
I got onto the support chat this AM and here was the result:

I see that your system is reporting it's data incorrectly due to a potential meter misplacement, I am going to escalate your situation to my tier2 team now. Please give me a moment.
Okay, I have submitted your case for investigation. Here is the ticket number. xxxxx
Going forward the team is going to complete a multistep process to attempt to resolve this issue remotely. They will investigate to identify the issue, modify any settings or firmware on your system, monitor those changes for a few days to ensure that we have data on whether or not the solution appears to be permanent or not. After they conclude this process they will either assign the case back to me to verify that our solution is reflecting the same way on your end. If you do not hear from me personally, then it's possible they will need to assign the case over to our scheduling team for a physical investigation to take place. This entire process can take between 7 - 10 business days, depending on the resolution.
 
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Ok, they came and fixed the coolant leak. They're still working on the erratic power flows.

But I think I found a clue. You can see in my post #4 above, Tesla added two CTs to measure the whole-house load from the grid.
Each of the two CTs for this transmitter attach to the two main service lines into the house. This info is fed back to the Gateway.

I believe these CTs are both misconfigured as monitoring 240v for each line, effectively doubling the reported current through each 120v feed. They should be set to 120v each.

Here's how I know. Yesterday I re-installed my sense meter also on the main to service feeds, and Sense is reporting just less than half what what's actually being pulled from the grid. I installed the accessory Sense CTs on the Essential Loads panel as a "dedicated circuit", so that's why you see that bubble.

Here's two screenshots from the Tesla App and Sense last night at a steady state. Tesla is reporting 4.0kW and Sense is reporting 1.5kW.

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But then I turned on my P85D to charge at 241v@32amps= 7,712w (remember this for later)

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Then here are what Tesla and Sense claim is the instantaneous grid demand:

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You can see that according to Tesla, the demand went from 4.0kW to 19.1kW, so a difference of 15.1kW
Whereas Sense reports 1,513w up to 8,970w -- a difference of 7,457k.

Notice that the actual power my car is charging is nearly exactly HALF of what the Tesla app is reporting for the power demand delta (7,457x*2=14.9kW)

And as soon as I stop charging, the Tesla app goes back down to 3.9kW.

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So if the Gateway and Inverter both think that the "whole house" load is 2x what the actual load is, I can see how the internal power flow calcs are confusing it, compared to what it's actually measuring. Unfortunately, I can't change these configurations myself. Luckily Tesla will be here to patch a whole they drilled into my office wall, so I hope to get it fixed then.