Kilowatt Plot / by Michael Johns

Kilowatt hour (kWh) is the standard unit of energy consumption, equivalent to 1000 watts per hour. For example an electric oven that consumed 1000 watts in an hour, or 100 watt heater that ran for 10 hours, both used 1 kWh of energy. On average, according to the US Energy Information Administration, an American household consumes just over 850 kWh per month. Looking at this plot, where each blue dot represents total kWh used each month, even in the dead of winter here in Alaska Casey and I stay well under the national average. Of course we don’t have an kids, don’t have air conditioning, and live in a small 800 square foot cabin heated by burning oil. Still, temperatures regularly dip below -10F in the winter, and we have to do things like plug in our cars to keep the engine oil warm, so I think we’re doing alright. Just for fun, I fit a simple linear model to our monthly energy consumption, which takes into account average monthly low temperature, day length on the 15th of each month, and number of days per billing cycle. The model (yellow line with shaded confidence region) predicts our monthly usage pretty well, tracking lower consumption during the longer warmer days of summer, and higher consumption during longer colder nights of winter. Of course the model isn’t perfect, but something odd did happen during the months leading up to 2017. A mystery that has yet to be solved.