After power off, strange numbers

[mongojarle]

Describe the bug
My grid-owner turned off power during the night for some work on the grid. As the HAN-sensor is powered by the meter, the sensor was also off during these 6 hours. After power came back, the accumulated monthly usage and cost went back to some seemingly arbitrary value. As demonstrated by the Home-Assistant log.
Also, during the power off period, the sensor has back-filled with a consumption of 0.13kWh each hour. Why?

To Reproduce
Power off sensor, them power on again? Have not reproduced this.

Expected behavior
Expected to have the usage and cost resume from last known value.
Expected usage during power off hours to be 0kWh.

Screenshots
HA log: https://imgshare.cc/htxvb00w
Hourly consumption: https://imgshare.cc/yh12adv3

Hardware information:

• Country: Norway
• Meter: Kamstrup
• Encryption enabled: N
• AMS reader: Pow-K

Relevant firmware information:

• Version: 2.5.7
• MQTT: Y
• MQTT payload type: HA
• HAN baud and parity: 2400 8n1
• Temperature sensors: N
• ENTSO-E API enabled: N

[ArnieO]

Also, during the power off period, the sensor has back-filled with a consumption of 0.13kWh each hour. Why?

What you see is normal; let me explain.

• Power meters in Norway transmit Total accumulated energy ("målerstand" / total kWh) only once per hour, at the passing of whole hour.
• The amsreader will during normal make a running estimate of the consumption during current hour, by integrating power * delta_time. But at the passing of whole hour, we get the exact value of latest hour consumption: The difference between two whole-hour kWh reading from the meter.

So what happens during such an outage?

We can see from your graphs that power was gone for a period of 5-6 hours. It started arter 23h and power was back again before 05h. We must the assume there was consumption in these two periods:

• After 23h up to the outage started
• From outage ended until 05h

At 05h the amsreader has two values for total kWh:

• Value read at 23h
• Value read at 05h, which is 0,78 kWh higher

It does not know what happened in-between, so the best it can do is to average the consumption over those hours - and indicate 0,13 kWh each hour-interval.

[mongojarle]

OK, makes sense for the consumption during the outage. But this does not explain the monthly accumulated consumption decreasing after the outage. This number should always increment up to the end of the month?
And as far as I know, this is not something that the meter sends, so it has to be calculated in the HAN sensor?

Edit: I updated the firmware mid-April, and all data on the sensor was reset during this update. I was on a firmware well more than a year old. So the thing only has data from April 11the I think it was. However, the accumulated values has been working fine up to this power outage.
Does it maybe take the last value the previous midnight and start adding from there? And because my power was out at midnight, it took the previous midnight as base?

[ArnieO]

Sorry, I didn't notice that.
And you're right: It does not make sense, this might be some kind of bug.
Here is the image you shared showing the problem: