Why do my calculated energy (kWh) values in Home Assistant differ from the Sigenergy app and my grid provider's meter?

[TypQxQ]

Q: I notice that the energy consumption (kWh) reported by my Home Assistant integration, the Sigenergy app, and my official grid meter never seem to match exactly. Why is this?

A: It's completely normal and expected to see differences between these energy readings. Here's a breakdown of the key reasons:

1. Energy is Calculated, Not Directly Measured:
   None of these systems directly measure energy consumption in kilowatt-hours (kWh) over time. Instead, they measure power in Watts (W) at specific moments. They then calculate the accumulated energy by essentially adding up these power readings over time (approximating the integral of power).

2. Different Measurement Intervals (Sampling Rates):
   Each system measures the power at different frequencies:

   • Sigenergy Gateway: Updates every 2 seconds in the Sigen App.
   • Sigenergy Smart Meter SDM630MCT: Updates every 5 seconds in the Sigen App.
   • Grid Provider's Smart Meter: Samples at its own rate, e.g., perhaps every 3 seconds for internal calculation, though reporting might be less frequent. (Note: Actual rates vary significantly by utility/meter. The key is that it's different from other systems.)
   • Home Assistant Integration: Depends on how often it polls data from Modbus and how long time each poll takes.

3. Timing Differences:
   Because the sampling intervals and exact timings differ, each system captures a different snapshot of your power usage, especially when usage fluctuates.

   Example: Imagine your inductive stove cycles power rapidly. A sensor measuring every 2 seconds might catch more peaks and troughs than one measuring every 5 seconds, leading to different average power calculations over short periods.

4. Impact of Load Variability:
   The more your power consumption fluctuates (like with inductive stoves, air conditioners, motors, or many small devices cycling), the larger the potential discrepancies between the calculated energy values will be. Constant, steady loads result in closer readings.

5. Minor Factors:
   Other factors can also contribute small differences:

   • Sensor Accuracy/Calibration: Each physical sensor has its own accuracy tolerance.
   • Calculation Algorithms: Slight variations in how the energy summation is performed.
   • Measurement Location: Grid meter vs. Sigenergy sensor vs. other sensors might be at slightly different points in your electrical system.

Conclusion:

Because energy (kWh) is calculated based on power (W) measurements taken at different times and different frequencies by each system (Grid Meter, Sigenergy, Home Assistant), it's practically impossible for their accumulated energy values to be exactly the same. Small discrepancies are normal and expected, especially when your home's power usage varies significantly.

[wattmatters]

Thanks for this, I noticed the differences in reported energy after my first full day of data collection. Not a small difference either (HA was 95.7% of Sigen reported PV generation). It's a shame the Sigen modbus registers don't include accumulated energy register values, then the two systems could align perfectly. My old Fronius used to provide the energy registers.

[TypQxQ]

Thank you. Sigenergy is working on it but if you want reliable info I would use a P1 meter and get the dta the grid company uses.

[DeepSpace7]

The Modbus data seem to me much more reliable than the app data. I have all the time much more grid import shown in the app than in reality (or via Modbus)

[AndyFlysJabs]

Also worth pointing out that current transformers are used in the gateway to measure currents in and out and that current is only one factor of power, the others are voltage and relative phase of each. given that all of these 3 measurements are analogue measurements they are only as accurate as the calibration made them. I would think that 5% or less as differences between you sigenergy and you HA calculated values and your retailers "in meter" measurements is totally acceptable and unavoidable. Being analogue in nature calibrations don't last forever, its why test instruments get sent to calibration labs on a regular basis so accuracy is reset back to that, that the OEM intended.