Add "Total consumption" as a possible energy source in the Energy dashboard

[pierrepaap]

Background
In some electrical setups (mine for example) it is not easily possible to have a "grisd consumption" source.
My provider cabling allows me to have access to the "solar production" and to the "total (or house) consumption" with the meters installed.
There is no economical or easy way to set up a "grid consumption" source

Request
Could it be possible to have an extra source in the dashboard (where is debatable) to allow to setup a "total consumption source" ?
This would avoid having to manually find solution to calculate a "grid consumption" that could be used as a source and do all these in the background. This would ease the life of some users and therefore UX.