Understanding Overall Efficiency
Many Tesla owners who check their metered electricity usage for charging are surprised that it can be nearly twice what the Model S reports using for driving. There are several factors that contribute to this:
The chart below shows the total meter-to-miles effiency accounting for these losses. As you can see, if you don't drive much, the efficiency goes down since the non-driving losses aren't amortized over a large number of miles driven. You can download the Excel file and put in your own assumptions for your Wh/mi driving, charger efficiency, etc.
Download MS Excel File:
If you don't have Excel, here is a PDF snapshot: