Group of measurements correct value on card, but not showing on chart

So the thing is I have 2 energy measurements solar panels and net usage.
But to see how much i really use, i want to add the 2 together and put all 3 measurements in a chart.

so the 2 direct measurements is fairly straight forward.
Then i created a group and put those 2 measurements as member of the group and i can see the sum of those 2 values on a card, which is correct.

However, i tried to add the group as time series to the chart, but it just doesn’t show.
and when i click through on the card, i just see an empty chart …

So i can see the value is correct, but HOW do i get it to show up on a chart ?


so after i woke up this morning, i saw that the group item now has a correct graph of my total.
In a chart i created myself.
HOWEVER, if i click through on the card, I still see an empty graph…

So my (wrong) assumption was, that when i grouped 2 items with historical data, it would also take the sum of that historical data, but it just populates it from the time of it creation.

So my actually question is, how do i make calculations based on historical data?