Difference In Daily Total Usage

I am comparing my Total Daily Usage from Sense to that of my local utility. I have noticed on some days it is very close and on other days it is way off.

For example:

12/5 - Utility = 89.714 / Sense = 89.93

1/1 - Utility = 79.251 / Sense = 106.843

What would cause the large difference on some days but not others?

I did a post on how to check correlation and isolate discrepancies here:

A few possible causes for discrepancies:

  1. Sense CT not completely closed - Sense number lower than utility
  2. Data loss from Sense - Sense number lower than utility
  3. Utility data issues - Utility number could be lower or higher

Possible sources for your discrepancy depend a fair amount on your utility and how they collect readings and provide to you. If you have a smart meter, as it appears you do since you can get daily data, then most likely your meter sends readings every 15min or hour. But not all those readings always make it through to the utility thanks to wireless communications issues. If data is missing, the utility will substitute estimated reads for actual reads.


One question - do you get utility data in chunks smaller than a day. That might help isolate.

You can also see one saga to sort out big discrepancies here. The culprit was actual reads vs estimated reads…

What do you mean?

The Original Poster is seeing discrepancies between utility and Sense, perhaps similar to what you were seeing. Pointed him to the data that answered why in your case.

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Thanks for the info Kevin! So I went back and did the report by the hour like you said and this is what I came up with.

12/5/2020 0:00 3.298 3.026
12/5/2020 1:00 2.905 2.67 2.715
12/5/2020 2:00 2.716 2.738 2.659
12/5/2020 3:00 2.759 3.179 2.295
12/5/2020 4:00 3.238 2.615 2.91
12/5/2020 5:00 2.636 2.639 2.605
12/5/2020 6:00 2.796 2.986 3.096
12/5/2020 7:00 2.893 3.18 2.906
12/5/2020 8:00 3.148 3.554 3.117
12/5/2020 9:00 3.244 2.723 2.35
12/5/2020 10:00 2.436 3.082 2.508
12/5/2020 11:00 2.871 3.492 3.434
12/5/2020 12:00 3.276 3.823 2.48
12/5/2020 13:00 3.755 3.722 4.141
12/5/2020 14:00 3.618 4.349 3.897
12/5/2020 15:00 4.331 3.465 3.353
12/5/2020 16:00 3.593 4.765 3.732
12/5/2020 17:00 4.862 7.902 5.384
12/5/2020 18:00 7.897 6.128 7.547
12/5/2020 19:00 7.049 5.721 5.696
12/5/2020 20:00 5.662 3.752 5.072
12/5/2020 21:00 3.773 3.538 3.379
12/5/2020 22:00 3.508 3.421 3.771
12/5/2020 23:00 3.45 3.462 2.922
12/6/2020 0:00 3.589 89.932 81.969

The first Hourly column is from my utility, the 2nd column is from Sense, and the 3rd is from my solar monitoring software.

As you can see they don’t always match up.

Some days Sense is close to my utility, sometimes less, sometimes more. My solar system seems to be different from both Sense and the utility. I don’t see any commonality between the three.

I double checked that the Sense CT’s are completely closed.

Any ideas are welcome.

A few questions…

  • Is the Sense column really Total Usage + Solar Production (negative) ?
  • What is your solar monitoring software ? Seems like it is more than just solar monitoring if the 3rd column is showing net usage ?

Assuming all of these are net readings I suspect that you have some kind of time misalignment between your utility and Sense. This happens very frequently because different companies define intervals differently. (Is the power measured for the previous hour or the upcoming hour ? Same if measurements from utility are in 15 min increments).

It looks like the Sense reading for any given hour is closer to the subsequent utility and solar hour. The first thing I would try if I were you is to shift the Sense data down by 1 hour, then plot your utility vs. Sense net usage in and X-Y plot. That will give you some idea of whether there is some kind of systematic or random variation.

ps: Looks like you have a Service-Side Tap solar setup and Sense CTs are installed correctly.

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Oh got ya. :slight_smile: I was wondering why I was being CCed. By the way, I got in contact with NV energy today and I made a pretty compelling case as to why my meter could be broken. They’re sending a tech out tomorrow to come take a look at it. If there’s something to be said here and they do end up getting some overcharged money back or something like that it’s one step towards getting equal Fairnest for everybody.


Thanks Kevin! I’m glad to hear that I have things installed correctly. That took me a while to get it done right in the beginning.

For solar monitoring I am using Enphase.

That’s a good catch on the offset of the time intervals! I moved the Sense measurements down one time slot and things appear to match a little bit better. However, as you can see some days things are almost the same, other days my utility is higher, and sometimes Sense is a little bit higher.

As you can see from the XY chart they follow the same trend, but sometimes a little different.

You can also see the % difference between the two on each given day. I would expect a +/- 1 to 2 % difference either way, but not more than that.

Your thoughts?

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Better in correlation than without the hour offset, but still not the max 1-2% difference you should be seeing.

3 thoughts:

  1. Try this form of an x-y plot, just comparing the two usage values at the same time. This type of x-y plot is going to be useful when you are comparing hundreds or thousands of readings and looking for patterns. Your comparison chart should look the one below once you get everything figured out.

  1. double check the time base that your utility uses, to understand where this offset is coming from. I have seen some cases where the utility actually does 15min usage updates and the way the intervals are defined can lead to a 45min offset with respect to Sense. The error, even after the time shift, could still be consistent with a time base offset issue, though if you don’t get the 15 min data from your utility, there might not be any further you can go along these lines.

  2. try to also figure out whether there is any way to tell when your utility is doing estimated reads of your smart meter. Together with other users, we have figured out how PG&E and NV Energy identify estimated reads in their exported data. Your time chart and associated error are consistent with estimated reads mixed in with actual reads like we saw in the NV Energy case. Example of a time comparison waveform showing many NV Energy estimated reads below - red is Sense, blue is utility reading. Dots are colored based on how many actual (vs. estimated) reads are done in an hour (4 reads of the meter per hour).

ps: Seems like you have very small solar component. In most cases with solar, I see several hours per day with negative net usage on Sense and utility.

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That’s great news… Gonna keep linking back to your original posting to help @Ray13, so you might get cc:ed a few more times.

Here is my x-y plot showing the comparison between my utility and Sense.

I actually just talked to my utility and they confirmed that the readings are done every hour. The number that shows next to 1:00pm is the amount used since the last reading at 12:00pm. If there is no reading at a given hour for communications reasons, then the amount would be cumulative for the previous two hours. For example if 12:00pm didn’t get read, then the 1:00pm reading would go back to 11:00am assuming that was the last good reading.

I’m not sure what you mean by a “small solar component”? I do know that at night when solar isn’t producing, I get a -21w value. During the day though, it is showing a positive number even if it is cloudy.

OK - that explanation from your utility highlights the offset. For Sense, the 00:00:00 (midnight+) data point is the usage for the time between 00:00:00 and 01:00:00. You should also note that that will affect your daily calculations.

That explanation also dispels the two possible correlation error sources I mentioned, though I’m still suspicious that your utility might be hiding a 15min read cycle under their hourly numbers.

The next thing I would do is plot a bunch more hours with the corrected offset using the x-y plot you just constructed and see if there is any correlation between the size of the “error” and other factors like time of day (color the dots for time of day like in the plot below). Multiple days might also highlight some larger outliers that could provide the key.

When I say smaller solar component, I mean size of solar system. My system is large enough that even in the winter, my net usage from my utility and Sense (Total Usage plus Solar Production) goes negative.

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To: @Ray13

Here is an analysis I did several years ago. Browse the whole thread. You might gain some insight from other posts.


Thanks Kevin, I’ll go back and apply the offset now that I know that is what it is doing.

My solar never goes negative, only at night when it isn’t producing. During the day when it is producing, I can see how many Watts are going to the house and if there is anything extra, is going back to the grid. If the panels aren’t producing as much as I need, then it shows how much I am pulling from the grid in addition to what my house is using from solar.

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Your results for many, many hours should be interesting…

My discussion on solar and negative readings really refers to the net energy, which is typically what your utility meter shows when one has solar. The meter and export will show positive energy when you have consumed more from the grid, than put out to grid from solar over the hour (net usage from the grid was positive). Conversely, the utility net reading will be negative when you have put out more energy to grid from solar, over an hour than consumed from grid (net usage from the grid was negative). My solar array is big enough that for some hours in the middle of the day, my utility hourly data goes negative (Have put out more energy to the grid than taken from it). But you might not have the same kind of net meter.

It would be interesting to hear how your utility deals with solar - that might be another piece of solving the mystery.


My utility tracks usage and generation (the amount I send back to the grid). On my bill they subtract the generation from my total usage to come up with a new total usage and then bill me on that.

My house will will sometimes use directly from the solar as it is being generated. What it doesn’t use will get sent to the grid.

This typically happens in the middle of the day.

I am working on putting together a spreadsheet that shows what my utility says I used on a given day, and what my solar app says I imported, produced, consumed, exported, and net imported.

We’ll see what trends come from that.

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Thanks, this screen offers a little more clarity. It looks like the number you are charting for all three data sources is “consumed” electricity (Total Consumption in Sense-speak), not “net usage”, because your “net usage” would have gone negative on a day like this.

A couple notes:

  1. Your metering setup is different than mine if your utility can actually calculate your “consumed” electricity - my meter only reads the “to grid” and “from grid” data and rolls it all up into a net reading every 15 minutes.

  2. Counting the number of bars in this graph, it looks like your power company and your inverter produce reads for 15 min intervals even if you only see exported hourly data.

No biggie. Does he live in Vegas too?

Different location - utility is CMP.