idea based upon the 'aquarium', filling a space idea. Dotted line represents target for the specified time period. 

more abstract idea:

appliances are grouped and size of their bubble indicates the amount of energy they have used in a given time period (e.g. current day). A simple visual way of seeing how much energy has been used.

dotted rings around the circles indicate the maximum usage that has been set by the user in order to meet their daily/weekly/monthly targets. You can quite easily see which appliances have used more or less than expected and adjust settings accordingly, or alter your usage.