Electrical Energy is the product of Power and time. If “E” is the Electrical consumed by an appliance having Power rating “P” in time “t’ ,then
E = P x t
The unit of Power “P” is watt and Unit of time “t” is hour, Thus
E = Watt x hour
E = KiloWatt-hour
Commercially One KiloWatt – hour is called the 1 unit of electricity.
Power distribution companies charge the electricity to the consumer on the number of units consumed.
For Example: We have appliance having power rating of 2 kW and we are using the appliance of 2 hours each day. The number of units of electrical energy consumed by the appliance in 30 days
E = 2.5 x 2 x 30 = 150 kWH = 150 Units