Difference In Daily Total Usage

CMP or Central Maine Power which has recently been rated the worst utility in the US! We are fighting them up here now because they are trying to force a new high power line from Quebec, Canada to Southern Maine to benefit MA. We don’t want it because it’s going to destroy our wilderness and be of no benefit to Mainers.

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So I am looking at my solar software (Enphase) right now and comparing it to my Sense software. Enphase is showing me 12.9 KWH produced so far today and Sense is showing me 9.8 KWH produced. Why the discrepancy?

Remember the possible 1 hour offset difference. Sense is also typically a little slower to update new aggregated hours. Enphase might update every 15 minutes. So look closely at how much time each total represents…

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I think that is the problem. Right now Enphase is showing 15.9 and Sense is showing 15.2. Sense is “catching up” so it most likely is just due to a time difference in the measurements.

One other note - Sense Solar users generally report seeing Sense solar numbers that are 3-5% less than the inverter reports. There are mixture of theories on why, but I have found that the Sense solar number when used with Sense Total Usage, matches the net usage from my utility better than the inverter data does.

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That’s better! When I use the Net from Sense and the Net from Enphase, my % difference is between 1%-3%. I can live with that.

The difference between Enphase and my utility Net is -3%-7%. Not as good and a couple days I need to look into. This is the reason I’m doing this whole exercise.

The difference between Sense and my utility ranges from -4%-6%. This seems about the same range as Enphase and my utility.

It appears that Enphase and Sense are consistent in that they both have the same range difference, which makes me believe my utility isn’t always right. The fact that Enphase and Sense have a much smaller margin difference when compared with each other, tells me that may be true!

That’s good news. One thing I’m not clear on for your setup is the data sources.

Utility - Usually, a user with solar, will have a single net meter that only provides net readings, to grid readings and from grid readings - nothing that actually reads the solar production, though I have seen one case where the utility did a double metering. Does your utility provide net usage and solar production separately ?? If so, where does it get the solar production ? Another meter or from Enphase ?

Enphase - usually a solar inverter has no knowledge of the house usage or utility net usage. Where does Enphase get the house usage from ??

I ask these questions because mixing and doing arithmetic on data from difference sources can either exacerbate differences or cancel differences depending on the biases of each source.

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@chrisseivert24 I live in Maine.

@kevin1 My utility (CMP) tracks net usage coming into my house, and they track net power coming from my solar back to the grid. You will see that in their data which I retrieved from my account. In the 5th column you will see either a 10 or a 20. The number 10 represents power coming into my house. The number 20 represents my solar power going out to the grid from my house.

30011986103 2300295521 L112416992 1/3/2021 12:00 10 3.022
30011986103 2300295521 L112416992 1/3/2021 12:00 20 0.158
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OK - then you have a traditional net meter that gives you hourly “Delivered” (from grid) and “Received” (to grid) data. And as you have highlighted, the only way you can compare Sense and utility results is via the net (utility Delivered - Received vs Sense Total Usage - Solar Production). Where does Enphase get it’s net usage data ? Does it communicate with your meter ? Or does it have its own set of CTs for measuring current entering your main panel ?

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Enphase has it’s own set of CT’s, which are considered “Revenue Grade” as that call it in the industry. They are bolted right to the main electrical leads in the panel as opposed to clamps like Sense.

IQ Envoy, Envoy-C, Envoy-S | Options & Resources | Enphase

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