Add a total kWh to the "Monitor individual devices"

[dannytsang]

I would love to see a total kWh for the Monitor individual devices in the energy dashboard.

It would allow me to see how much out of my total household usage is tracked against individual devices.

For example if my home has used 8.6kWh:

and these are my individual devices:

The above total for all the devices equate to 4.75kWh. If the dashboard could show 4.75 then I can see my devices account for 55% of my total household electricity usage.