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Powerwall Readings Discrepancy

Powerwall Readings Discrepancy

Does anyone have a situation with their reported Powerwall grid consumption being more than an order of magnitude out against what their smart meter records?

In my case the Powerwall app reports grid usage/import of 0.2 kWh from the grid for a day. However my smart meter reported usage of 4.063kWh for the same day.

Looking at my smart meter readings the figures are measured down three decimal places whereas the Powerwall app records figures to one decimal place. I have spoken with Tesla who have advised that there is no issue with my Powerwall and my energy supplier who could not find any issues with the smart meter.

When I look over the course of the day the majority of half hourly readings from my smart meter are below 0.09 kWh so I assume the Powerwall is unable to measure that?

gregbrew | 21. Oktober 2019

I wouldn't worry about decimal places. This goes much deeper than that. Is the utility smart meter reporting only what you actively pulled from the grid that day (without considering what you sent to the grid), or is it a "net" value that is the difference between what you pulled and what you pushed to the grid? Because there are so many variables with solar and batteries, it can be quite confusing when you try to read the bill and/or utility website.

oliver11 | 22. Oktober 2019

The meter is reporting what is actively pulled from the grid and doesn't measure export. I know if I am exporting, the meter readings show zero usage.

The half hourly values for a three hour period starting at midnight look like the following.

0 0.089
0 0.09
0 0.091
0 0.092
0 0.091
0 0.09

Tesla grid consumption values are on the left and smart meter values are on the right.

jrweiss98020 | 22. Oktober 2019

The meter itself uses some power, and will draw that directly from the grid. The Powerwall will not see it.

rlwrw | 22. Oktober 2019

It depends on where you are located. NV Energy here in Las Vegas has a neat chart on the account page that shows the various states of use for each day, week, month or year. Used from the grid (If more used from the grid), wash (sent = used), and sent (If generating more than used.)
Now that the air conditioner does not have to go on anymore, I am seeing a lot of green below the net zero line in my account. (More sent to NV Energy than received.)

oliver11 | 22. Oktober 2019

I'm located in the UK.

From a quick search, the following article suggests that the smart meter might use about 1kWh over the course of the whole year.

https://www.thisismoney.co.uk/money/experts/article-4607552/How-electric...

The usage in my case seems to be about 3-4kWh a day.

My supplier doesn't receive export figures from my meter as I have a separate meter for my generation which I have to submit manually.

charlesj | 23. Oktober 2019

@oliver11, not the meter using the power as that would be 0.11 Watt hour of usage and that should be on the power companies dime, not the homeowners. :)

charlesj | 23. Oktober 2019

By the way, that 3 decimal shows power down to a watt, .001 kWh

oliver11 | 24. Oktober 2019

Thanks charlesj I was just caught up in decimal places.

I guess the question is, can the Powerwall measure values less than a 100 watts? If it is not able to, that would explain the discrepancy in the readings I see.

gregbrew | 25. Oktober 2019

When doing post-installation checkout of my two PW system, I asked the Tesla installation Team Lead about the little (100W) momentary power flows that occasionally showed up on the POWER FLOW diagram. He said to ignore them, as they are measurement artifacts.

Noam | 25. Oktober 2019

Greg - you bring up a good point. Since the different measurements aren't being taken at the *exact* same moment, and since it is common to need more than one of the measurements to calculate some of the numbers. If you're measuring solar production and gross (house) consumption, you can calculate the net (utility) consumption. If you are measuring the solar production and net (utility) consumption, you can calculate the gross (house) consumption. But since those numbers are *always* fluctuating a little bit, the time delay between them (even if only a few milliseconds) is enough to cause a certain (small) inaccuracy in the reading. This is the same reason why the "Now" tab in the PowerGuide would sometimes show a spike/dip in consumption if the solar production had a spike/dip (usually due to fast-moving clouds). These consumption measurements (other than the utility's net meter) tend *not* to have revenue-grade accuracy. You need different equipment to be more precise.

oliver11 | 26. Oktober 2019

It's the cumulative amount over the day that causes me the most concern.

I wasn't expecting the utility meter to be reporting more than 10 times higher usage compared to what the Powerwall reports. I was trying to determine if this is normal and if it is then not much can be done about that.

gregbrew | 26. Oktober 2019

The real question should be...are both meters actually reporting the same measurement, or is one reporting gross, and the other net?

smaches | 26. Oktober 2019

Could this be one of those pesky 'calibration' issues of the monitors in his TEG?

oliver11 | 27. Oktober 2019

My utility meter is recording the gross consumption I'm sure.

It doesn't record any excess I send to the grid. When excess solar is being sent to the grid this shows up as 0 on my meter (regardless of how much energy is being exported). I have a separate meter which records the generation.

I assume the Powerwall records the gross usage? Since it gives the separate figures for the energy taken from or being sent to the grid.

Noam | 28. Oktober 2019

It still may be a calibration issue. I strongly suggest calling customer support, and asking them to check the calibration. I also suggest calling your utility, and asking them to explain *exactly* what the display on your meter is telling you (since every utility can configure that display differently).