Identifying baseline consumption
I don't think there is need for very complex methods here, I would take a look at several granularity levels and take means for these levels. One important thing is if all the households are in the same area/timezone. After establishing this I would first take the general mean and see per household how they compare to this, then do this for every halfhour segment of the day to get rid of time-of-day seasonality, do this for day of the week, month of the year etc. It really depends on what you want to know what to do with this data.