Why do the historic meter numbers constantly change?

I've written a script that looks at the half-hour energy grid import from givenergy API (same data you see on the energy charts). I'm merging it with Octopus Agile today cost to give me a sense of how much money I've spent today so far.

Works great, the problem is the kWh usage for the half hour slots constantly changes! Example today at approx 8.30am:

2024-01-05 05:00:00 Usage: 0.090kWh
2024-01-05 05:30:00 Usage: 1.510kWh
2024-01-05 06:00:00 Usage: 0.110kWh

and now at 10am:

2024-01-05 05:00:00 Usage: 0.090kWh
2024-01-05 05:30:00 Usage: 1.500kWh
2024-01-05 06:00:00 Usage: 0.110kWh

I know its small discrepancy here, but then multiple slots change randomly over time. Not life or death as I get billed what I get billed, it just doesn't really help put any faith in the data if it changes after the fact.

I could understand if it was the most recent slot, as it takes some time to "process" and appear... it seems really odd to commit to a meter reading value of x, then many hours later change it to y

pacemaker
Had something similar last couple of days, so curious to see what is causing it. I attached the two screenshots that show the discrepancy.


Bear in mind I was away on holiday that day so I find it bizzare that I draw 1.5kwhs from the grid in the afternoon. Inverter data confirms that as well!

dorosde

That's slightly different to my issue, but equally weird! What does the ENERGY grid import chart show for that timeframe? The bar chart you are showing is data from Octopus (and your smart meter), rather than the GE meter data. What's this one show:

pacemaker
Even more weird!

5.99 kWh of import which makes more sense and aligns with the power curves. No import in the afternoon though!

There have been many posts previously highlighting that the GE energy charts are not accurate, more a guide of the trends as they are possibly based on the snapshot readings once every 5 minutes.

A more accurate set of readings can be seen under 'My Inverter' 'Meter Data' in raw data form, but even these are subject to the accuracy of the EM115 meter with it's CT clamped around the house grid incomer cable.

The default sort order of the data is most recent at the top, so request yesterday on the date and you get the last reading of the day showing.

pacemaker This kept bothering me as it was carrying on! Checked the time on my smart meter and it was two hours behind. So If I was charging the battery between 00:00 to 00:30 real time the smart meter was reading it as charging 22:00 to 22:30 instead! Raised it with Octopus that they will investigate, correct the time on Smart meter and correct my bills since joined Agile (since 10/12/23)

Simon_C yeah I am not worried about the total day, I just want the half hour energy report to keep the same value each half hour rather than say its one thing at 1pm-1.30pm, then change it 3 hours later, then change it again 3 hours later. You'd think surely once its processed a 30 min window that value is set in stone.