A watt (W) measures the rate at which energy is produced or consumed. 1000 watts is called a kilowatt (kW). Electrical energy is usually sold by kilo watt hour that is 1 kWh = 3.6 MJ which is the product of the power in kilowatts multiplied by running time in hours. Electric utilities measure energy using an electric watt meter, which keeps a running total of the electric energy delivered to a customer. We usually pay for our electrical energy based on the amount of kilowatt hours (kWh) used - this is the equivalent to 1 kW of power expended over 1 hour of time. Let’s start with the basics- A watt (W) is a unit of Power, and power is the rate at which energy is produced or consumed. A watt measures rates of power over a time period. Electrical energy is energy derived from electrical potential energy or kinetic energy. When used loosely, electric energy refers to energy that has been converted from electric potential energy. This energy is supplied by the combination of electric current and electric potential or voltage that is delivered by an electrical circuit. At the point that this electric potential energy has been converted to another type of energy, it ceases to be electric potential energy. Thus all electrical energy is potential energy before it is delivered to the end-use. Once converted from potential energy, electrical energy can always be called another type of energy that is heat, light, motion, etc.