You pay for energy, not power. The simple formula for energy is power x time. This is what "kWh" means... 1 kilo-Watt used for one hour. When calculating tot

You pay for energy, not power. The simple formula for energy is power x time. This is what "kWh" means... 1 kilo-Watt used for one hour. When calculating total energy utilization for a period of time during which power varies (your TV is turned on and off, air conditioner cycles, etc.) the calculation effectively entails the integral of power plotted against time. Another way to put it is that the energy is the area under that curve.