I'm Pre-PTO, in self-consumption mode, but utility meter shows that I'm consuming and exporting significant energy

[gravedee]

I'm in So Cal, on SCE, residential single-phase utility power, pre-PTO since May 5 with 11.2 kW of solar, a Powerwall+ with the 7.6 kW Tesla Inverter, Powerwall 2, and Gateway Backup 2. The app powerwall settings show Self-Powered and 'No" for Permission to Export. Backup reserve is set at 20%. My batteries have never below 35% since May 5. I have stayed under the max output of my 2 Powerwalls since except for 1 hour. So theoretically, virtually all of my power should be coming from solar / battery, and indeed, the App shows a net grid use of -1.8 kWh since May 9. Despite all this, the utility says I'm using 8 kWh on average per day.

In the process of troubleshooting I found that the meter is showing a draw (positive wattage, i.e. "spinning" forward) when I have a load running on one split phase / hot leg, but showing an export (negative wattage, i.e. "spinning" backwards) when I have a load running on the other split phase / hot leg. The amount of wattage the meter shows, positive or negative, is equal to the net difference in loads between the two split phases. In the troubleshooting process I was able to turn on loads on each split phase to effectively zero the meter out to show no draw or export. Any 240 volt load will not show up on the utility meter because 240 volt loads evenly pull power from both phase, so it's a net zero at my meter.

Is this normal or indicative of a problem? What type of problem? I should not be drawing power, and I should not be exporting, so it has to be a problem, right?

I sent all this to my certified installer and am waiting for a response, but hoping someone with some experience or expertise can tell me I'm not crazy in thinking something is really wrong.

 

[arnolddeleon]

Not normal [EDIT: Misread the post and posted "Normal" originally]

 

[yblaser]

I don't think that is normal.

Do you have a whole home backup and all your loads are behind the gateway?

I know for the solar CTs they can be configured to use a single CT and double the reading since it is a 240V source. Your system is behaving like your site/grid CTs are configured that way, although I do not know if that is possible in the configuration.

 

[tomuo]

They need to flip the polarity of one leg of the grid monitoring CTs. Very common installation mis-step.
Should be trivial to do via the remote management login page.

 

[gravedee]

I don't think that is normal.

Do you have a whole home backup and all your loads are behind the gateway?

I know for the solar CTs they can be configured to use a single CT and double the reading since it is a 240V source. Your system is behaving like your site/grid CTs are configured that way, although I do not know if that is possible in the configuration.

Yes, I have my whole home backed up. Separate panel with all the circuits behind the gateway. I am able to "Go Off-Grid" successfully. When I do, the utility meter goes to zero - showing no consumption and no export.

 

[jrweiss98020]

If you're using your solar pre-PTO, open the main breaker to the grid.

 

[yblaser]

They need to flip the polarity of one leg of the grid monitoring CTs. Very common installation mis-step.
Should be trivial to do via the remote management login page.

It sounds like the OP's system is sensing and powering 240V loads which I wouldn't think would be the case for a flipped CT. Am I missing something?

 

[gravedee]

It sounds like the OP's system is sensing and powering 240V loads which I wouldn't think would be the case for a flipped CT. Am I missing something?

That's what I'm thinking. I don't see how a flipped CT affects what I'm reading on my utility meter. Utility meters don't measure what is on a CT. The utility meter IS the CT, in a manner of speaking.

 

[aesculus]

It sounds like the OP's system is sensing and powering 240V loads which I wouldn't think would be the case for a flipped CT. Am I missing something?

Well except he said Utility Meter and not the Utility value from the Tesla App.

So if the Utility Meter is actually receiving power when only one phase is active something is odd. Maybe the OP just used the wrong term and then yes, CT wrong.

 

[gravedee]

Well except he said Utility Meter and not the Utility value from the Tesla App.

So if the Utility Meter is actually receiving power when only one phase is active something is odd. Maybe the OP just used the wrong term and then yes, CT wrong.

No - I meant what I said. The utility meter (not to be confused with what the app shows, which is almost always 0 grid usage) is showing positive (consumption) or negative (export) wattage depending on which leg has the most load. From what I can tell, the number that displays is the net difference. I can turn loads on from both legs to cancel each other out. For example, my toaster oven and microwave are on different legs. If I turn both on at the same time, the meter reading doesn't jump much. If I turn only one or the other on, the meter goes from about 300 - 400 watts normal background consumption to about 1.7 kW consumption or -1.4 kW export, depending on which appliance I turn on. If I turn on a 240v load, nothing happens because a 240v load pulls from both legs evenly.

 

[jgleigh]

Could it be a bonding or grounding issue? I've been trying to think about how the meter would only see power on one leg or the other, but I'm not coming up with any good ideas. Anyone a certified electrician?

 

[arnolddeleon]

I misread the original post. I thought the OP was indicating one phase was importing at the same time as another phase was exporting but the net was zero. That is normal, however what they actually wrote which others correctly understood is NOT normal.

They need to flip the polarity of one leg of the grid monitoring CTs. Very common installation mis-step.
Should be trivial to do via the remote management login page.

This is the likely situation.

 

[gravedee]

I misread the original post. I thought the OP was indicating one phase was importing at the same time as another phase was exporting but the net was zero. That is normal, however what they actually wrote which others correctly understood is NOT normal.


This is the likely situation.

I don’t see how monitoring CTs has anything to do with my situation. This is the Southern California Edison utility meter that I’m looking at - showing current flowing in and out. The utility meter doesn’t care about CTs. It is its own current measuring device. And keep in mind I’m pre-PTO, the app is configured that way, so I shouldn’t be exporting anything beyond a trivial transient watts here and there. I shouldn’t be importing anything either because I’m in self-powered mode, my batteries have never been lower than my reserve percentage, and they can more than handle the day to day loads I run.

 

[jgleigh]

@gravedee Can you post the four screens from a full day? I'm curious what the Tesla app is showing.

 

[arnolddeleon]

I don’t see how monitoring CTs has anything to do with my situation. This is the Southern California Edison utility meter that I’m looking at - showing current flowing in and out. The utility meter doesn’t care about CTs. It is its own current measuring device. And keep in mind I’m pre-PTO, the app is configured that way, so I shouldn’t be exporting anything beyond a trivial transient watts here and there. I shouldn’t be importing anything either because I’m in self-powered mode, my batteries have never been lower than my reserve percentage, and they can more than handle the day to day loads I run.

The load CTs is how the Powerwall (App in your words) figures out what the load is and controls the output of the inverters. This control isn't perfect so you'll see a small amount of transient buying or selling if things were normal. It they are backwards/wrong then the Powerwall system will also be wrong in what it generates, this result is unexpected imports or exports. You will see the net result in the utility meter.

 

[gravedee]

@gravedee Can you post the four screens from a full day? I'm curious what the Tesla app is showing.

First of all, I wanted to thank everyone helping out here - it's an interesting problem. Maybe it's just a flipped CT, the Tesla app definitely is not showing the same thing that the utility meter is showing. Here are some relevant screen shots.

First - here is June 10 (a very overcast day), according to the app, and then, according to SCE.

I did an experiment. The first photo is my meter under little to no load - just a few lights and then whatever electronic stuff is running all the time. Then, in this sequence, I took a photo of my meter and app under the following conditions:

Toaster oven (on Phase A) on, Microwave (on Phase B) off - shows a positive load of 1.9 kW
Toaster oven off, Microwave on - shows a negative load of -1.58 kW
Toaster oven on, microwave on - shows a positive load of .15 kW

light load, nothing on:

Toaster Oven On:

Microwave on:

Both on will be in the next post.

 

[gravedee]

Both Microwave and Toaster oven on:

 

[jgleigh]

I'm stumped. Something isn't setup right. I've seen installs where they added CTs that weren't needed and it confused the Gateway. You'd have to look inside your breaker panels and Gateway to really figure out where everything is wired up. Probably best to get your installer back out and show them these pictures.

 

[gravedee]

Coming back to edit this 8 days later with an update in case someone stumbles onto this post. The installer came out and found that one of the grid supply CTs was set to 'none' instead of site. Once it was set to site, everything is functioning normally.