kWh to mpg.

[Fishettibean]

Someone with solar panels might well use a negative figure I guess.

It will be 0p or very low Xp for solar, and the few that do get FIT payments for solar generation, that will go to paying for the panels.

The only way to get negative electricity is to be on octopus agile tariff and hope to see a negative prices. Which i think last happened last year....