I figure my sump used to account for $20-30 in a typical month. Summer months had A/C, "shoulder months" like October, April, May when I might use an electric space heater in lieu of lighting the wood stove could be high some years, low others.
11/2015 and 2/2016 were low because of the drought hardly ever had my sump running, while cold enough I was burning wood.
Now my electric bills over the years have quite a bit of variability -- 664kWh/month average, but with a standard deviation of +/- 304kWh.
I'm hoping once I'm back to using the wood stove, this month's bill will be my new Fall/Winter/Spring bill. Summer being higher due to A/C usage.