Does Solar Power Non-Backup Leg At All?

[gcsutton]

I have 16kW of solar and 6 PowerWalls. The monitoring app does not seem to recognize power changes (like 2 stage AC or oven turning on) on the non-backup leg.

For example, right now I have 11KW of solar being generated. The app says I'm consuming 1kW in 'Home' and 10kW are going into the PWs., nothing to/from the grid. Powerwalls are at 80% charge.

However, if I turn on both my large oven and the AC, which are both on the non-backup leg, nothing changes in the app. Power from solar, power to the 'Home', power to the PWs, and to/power from the grid stay exactly the same, no effect at all.

My theory for this behavior is (1)Home CTs are in the backup leg and can't 'see' the power to the non-backup leg or (2)solar can't get to the non-backup leg no matter what., or (3)some installation issue.

Also, even if the CTs are in the backup leg, wouldn't the PWs see that some solar was going to the non-backup leg as a reduction in their incoming power?

I quizzed the installers on this point and they said, no problem, as long as you have power from the grid then power from the solar and PWs will get to the entire house. You only lose power to the non-backup leg if the grid goes down.

Any thoughts on this are greatly appreciated

 

[BrettS]

So it’s a little complicated. The tesla system doesn’t directly measure the amount of power that your home is using. Instead it measures how much power your solar system is producing and how much power you are sending to or receiving from the grid and with those numbers it calculates how much power your home is using.

However, in your case it seems like the CT’s that should measure grid consumption are placed on the lines the feed the TEG, and not the lines coming from the grid. This will cause your system not to see the loads in your non backed up panel. The CT’s come pre installed in the TEG, but normally for an installation like yours the installers would move them so they were in front of your non backed up loads panel. This would allow it to monitor the devices in your non backed up loads panel. I don’t know if there was a technical reason that prevented them from doing this.

However, that said, your solar power will still power the loads in your non backed up loads panel. Once your powerwalls are full and the system starts sending excess power to the grid then the devices in your non backed up loads panel will use solar power first, if it’s available. However, because of the placement of the CT’s this won’t actually show up on the app.

If you are wanting to operate in a self powered or advanced mode then this is not ideal because the TEG won’t be able to see those loads and your system won’t be optimized to be self powered or to reduce your consumption during peak periods in the advanced mode. I would suggest working with your installers to see if they can move your CT’s.

 

[miimura]

When I had my Powerwall system installed in 2018, the Grid CTs were factory installed on the input to the Gateway switch. The system was completely blind to any consumption from non-backup circuits in my main panel. This concerned me, so I opened a case with the installer and they extended the CT wires into the main panel and placed the sensor clamps on the conductors between the main breaker and main panel. My Gateway is fed by a 125A breaker in the main panel. Since the Grid CTs were relocated, all household loads are measured on both the backup side and grid side (non backup) of the Gateway.

 

[gcsutton]

Truly appreciate the information from BrettS and miimura!

I happened to have some pics of the before and after installation in the main existing panel. Now that I know what to look for, I put together the comparison pic that's attached.

As Brett S suggested, it looks like the Tesla CTs are on the non-backup leg, on the house side of that leg's main breaker. There is a subpanel downstream from this point inside the house.

However, based on miimura's response, the CT's should be on the grid side, measuring the total house load at Point A (grid input)? I already have white Sense CTs at that point that pre-date the solar installation.

 

[BrettS]

Yes, you want the tesla CT’s in the same place that the Sense CT’s are. You can probably just move them yourself if you feel comfortable doing that, but be aware that they are directional, so you want to make sure you get the polarity correct.

 

[miimura]

Yes, you want the tesla CT’s in the same place that the Sense CT’s are. You can probably just move them yourself if you feel comfortable doing that, but be aware that they are directional, so you want to make sure you get the polarity correct.

This is probably correct. Although, it looks like you may have an Auxiliary Neurio installed in the main box. If you have a Gateway 2 installed, you have to be careful to make sure it's configured correctly because it may be installed on the Sub-Panel for a reason. If the Neurio is Auxiliary to the CT measurement system in the Gateway 2, it may be possible to install another set of CTs on the Main input next to the Sense CT. That would require software configuration in the Gateway to properly designate the measurement.

In any case, I would just call Tesla or your installer, if a third party, and tell them your observations about the A/C not showing on the load chart and have them remedy the situation.

 

[BrettS]

I suspect the auxiliary Neurio was installed due to distance from the gateway, but @miimura is probably right that the safest option would be to call the installer and have them fix it.

However, if you are comfortable working in the panel I don’t think it would hurt to try to switch it. It shouldn’t damage anything and if you start getting funky readings in your app you can always move the CT’s back. Again though, if you do decided to do this, pay attention to their orientation and which leg they are on.

 

[charlesj]

So it’s a little complicated. The tesla system doesn’t directly measure the amount of power that your home is using. Instead it measures how much power your solar system is producing and how much power you are sending to or receiving from the grid and with those numbers it calculates how much power your home is using.

....

How is the battery get calculated then. Isn't it also gets sensed and calculated by the gateway?

 

[BrettS]

How is the battery get calculated then. Isn't it also gets sensed and calculated by the gateway?

The batteries do their own measurements. They have a communication cable that connects to the TEG and they report their own consumption and production data through that.

 

[gcsutton]

I'd love to experiment by moving the CTs but the possibility of a TEG configuration change means I'll probably just call Tesla. They were the installer.

Yes, the Neurio is a long way from the TEG.

Really appreciate the spot on advice.

 

[charlesj]

The batteries do their own measurements. They have a communication cable that connects to the TEG and they report their own consumption and production data through that.

So, the battery's brain decides when to charge, how fast, etc, in concurrence what was selected in the app, backup, self power or advanced? And Gateway just communicates to Tesla and calculates the amount of solar production and battery charge or dischage amounts?

 

[miimura]

So, the battery's brain decides when to charge, how fast, etc, in concurrence what was selected in the app, backup, self power or advanced? And Gateway just communicates to Tesla and calculates the amount of solar production and battery charge or dischage amounts?

That's backwards. The Gateway is the brain and controls the logic and commands the batteries what to do.

 

[BrettS]

So, the battery's brain decides when to charge, how fast, etc, in concurrence what was selected in the app, backup, self power or advanced? And Gateway just communicates to Tesla and calculates the amount of solar production and battery charge or dischage amounts?

Yeah, like @miimura said, the gateway is the brain. You asked how the battery current is sensed. The batteries sense and report their power consumption or production to the gateway, but the gateway still tells the batteries what to do.

 

[astrorob]

i just got my PWs installed (after a year of waiting as some of you might remember.) all circuits save 3 are backed up (EVSE, 2x AC compressors). to the point of this thread - yesterday i wondered what i would see in the tesla app if i charged my car. to my relief, the TEG sees the load from the EVSE, which means i can use the TEG grid power measurement for PVOutput.

however, this load caused the powerwall to start discharging into the house, which makes sense i guess but i did not expect that. i thought part of the point of segregating those loads was to make sure the PW didn't discharge when they are present.

is this the expected behavior?

 

[jjrandorin]

i just got my PWs installed (after a year of waiting as some of you might remember.) all circuits save 3 are backed up (EVSE, 2x AC compressors). to the point of this thread - yesterday i wondered what i would see in the tesla app if i charged my car. to my relief, the TEG sees the load from the EVSE, which means i can use the TEG grid power measurement for PVOutput.

however, this load caused the powerwall to start discharging into the house, which makes sense i guess but i did not expect that. i thought part of the point of segregating those loads was to make sure the PW didn't discharge when they are present.

is this the expected behavior?

Yes, that is expected behavior. In a normal setup, the non backed up loads are not backed up, BUT seen by the system so they can be powered by the powerwall. When you have grid power (which should be "most times") those loads will consume powerwall power (or not) based on the mode your powerwall is in.

Your solar power can help provide power for those non backed up loads as well. The only difference is, if you have an outage, those loads dont work / will not be powered. This configuration is "normal" and what most want, as it enables them to use solar and or powerwalls to offset those non backed up loads as well.

Its possible for those loads to be invisible to the system (not seen at all) based on CT placement, but If the system sees the loads, they are part of the consumption, and will be provided power by the powerwall or not based on whether the powerwall is providing house power at the time or not.

Congratulations btw, I remember you getting started a long time ago.

 

[astrorob]

Yes, that is expected behavior. In a normal setup, the non backed up loads are not backed up, BUT seen by the system so they can be powered by the powerwall. When you have grid power (which should be "most times") those loads will consume powerwall power (or not) based on the mode your powerwall is in.

Your solar power can help provide power for those non backed up loads as well. The only difference is, if you have an outage, those loads dont work / will not be powered. This configuration is "normal" and what most want, as it enables them to use solar and or powerwalls to offset those non backed up loads as well.

OK - makes sense. my eventual goal here is to go into cost-saving time-based mode. since i would only charge the car at off-peak rates, i guess it doesn't matter if the PW discharges at that time, since at that point any load-shifting is done. that is of course as long as that mode still has a backup reserve percentage that i can set. i guess because the system was just commissioned, this mode is not yet available to me (so i haven't been able to play with it.)

Its possible for those loads to be invisible to the system (not seen at all) based on CT placement, but If the system sees the loads, they are part of the consumption, and will be provided power by the powerwall or not based on whether the powerwall is providing house power at the time or not.

Congratulations btw, I remember you getting started a long time ago.

i think i wouldn't want to move the CT as then reporting grid consumption (or rather, home consumption) to PVOutput will become really difficult. it's already a little wonky if i want to keep reporting against my old system ID as it looks like i have to report some info from the inverter and the generation/home consumption info from the TEG.

thanks - i think it was october 2019 when i first contacted tesla and while some of the delay was self-inflicted, COVID really punched a hole in the schedule. but the main panel upgrade went really well and tesla even modified the schematic to fully leverage what the MPE subcontractor had done. still have to pass city and PGE inspection though, which as i understand it can be problematic in my area.