Same Home - Two Different Reports

Thought this might be interesting for some. I have two Sense monitors in my house: one is my main unit that includes solar, and a second one I use primarily to monitor two 240V circuits in my house via DCM. Both have the mains CTs / sensors around the same pre-meter mains for my house. My main unit uses the second port for solar while the DCM unit uses the second port for the two 240V circuits. Because of the different setups, my monthly reports show very different results: the Main Sense reports on total usage (Solar Production + Net Usage), while my DCM Sense only reports on Net Usage.

From my Main Sense Monitor

From my DCM Sense Monitor

  • No Always On because my Net Usage often goes negative
  • No Solar because my DCM Sense isn’t monitoring solar
  • No top movers, even though I have a bunch of learned and detected devices plus 2 DCM devices.

Thanks for posting! Could you comment on the percentage of usage provided by solar? I think I recall that Sense defines this as an average of the values calculated each minute, which can never exceed 100%. That might explain why your main report says 30% of your usage was covered by solar.

The average wattage for your second report is 288 watts, measured after solar cancels some of your usage. The average wattage from your main report is 2,202 watts, measured before solar cancels anything. The ratio of those two values is 13%, which would seem to indicate that solar covered 87% of your August usage. That is a far different number than the 30% reported with your main sensor.

@jefflayman , good question,

The second I posted I started questioning the numbers as well. I believe that my Main Sense Total Usage number is correct, and that the DCM Sense usage number is off for some strange reason. My Main Sense solar tab is entirely consistent with the 30% number.

I’m guessing that there must be something wrong with the Sense hourly/daily/weekly/monthy aggregation when the usage data is mostly negative… Here’s a view on my DCM Sense Signal section.

Thanks for the additional data. Here is what I see in that data:

Usage detected by your main is 1,6387.7 kWh per the app (rounded to 1640 kWh in the monthly report) over the month of August which has 31 days at 24 hours per day, thus average usage = 2,202 watts. Analysis matches the monthly report, ✓

Usage expected to be seen by the DCM should be the value listed as From grid minus the value listed as To grid. Let’s see: 1,149.6 kWh minus 195.8 kWh = 953.8 kWh (listed as negative 954.2 kWh under net solar production). If this is again divided over the number of hours in August, the DCM should be seeing an average of 1,292 watts. Instead it reports 288 watts, which is the discrepancy you note.

Regarding the percentage of solar production, 42% is listed next to net solar production. This is the value I would expect if dividing your total solar production by your total usage. The difference between 42% and 30% was discussed in a thread several years back, where a user called one net and the other coincident solar.

Finally, I noticed that the ratio of To grid energy to From grid energy was 17% while the ratio of To grid cost to From grid cost was 13%. That discrepancy probably just means that the time-of-use feature is working as intended for your household.

Yes - sorry I didn’t go into the calculation for coincident Powered by Solar. 30% = (Solar Production - To Grid) / Usage = (683.5 - 195.8)/1637.7 * 100% = 29.901%

I didn’t get as fancy as you - I just compared the Main Sense Net of -954.2kWh against the -210kWh registered in my DCM Sense report. I’m going to need to double check what’s going on with my DCM Sense because my main Sense is within a few kWh of my PG&E net usage at a monthly level. Sense says 954.2 Net for August and my Meter says 953.

Screenshot 2023-09-18 at 6.07.06 PM

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Very interesting…

There must be some weirdness that I’m not understanding. Even though my DCM Sense mains CTs are on the same mains that go into my PG&E, the hourly net USAGE from my meter differs from the Sense DCM Net some of the time, but is spot on (or close) for other hours.

Your equation for coincident solar is far simpler than I imagined. Thank you for explaining! The equation makes perfect sense when applied with your data as an example.

As for the DCM measurement of whole-house current not matching the equivalent measurement by your main Sense monitor, I suggest opening up the breaker box to look for a physical issue. Maybe there is a clamp partially open or a nearby conductor that is skewing the measurement. The technology in both energy monitors is the same (it is even supplied by the same manufacturer), so they should get the same result when measuring a given subject.


@jefflayman, OK mystery solved… thanks for the inspiration to go double check my CTs (I actually consulted my photos, instead). When I first acquired my second Sense monitor, it was to test out the 400A feature, because I have 400A supply with two parallel panels (see photo). When I put into service for DCM, my electrician apparently moved just the the second set of CTs with the sun on them. That means my DCM Sense is only measuring the Net for one of my two panels (the one with the solar feed-in plus most of the large loads - TVs, floor heating coils, etc.).

A good lesson in double checking assumptions.