Two successive prints :
One long print :
One small print + some idle time 
One week of prints :
One month of prints :
(everything here in PETG + PEI textured plate, european country / 220V)
Conclusions :
- Idle is indeed consuming 10 Wh since one of the past firmware update
- Max consumption is never higher than 70 Wh
- For a very rough calculation with approximation one could consider 1 hour of print = 100 Wh
- For an average usage (which is my case), one can consider a few kWh per month (like 6-10 kWh per month) - for comparison, without 3D printing, my monthly consumptions for the flat (lights, servers, …) is 500 kWh each month