Kilowatt - hour is the commercial unit of electrical energy. We have seen that power is the rate of energy consumed or delivered. If 1 joule of energy is used per second, we say that energy is used at the rate of 1 watt. In other words, if energy is used at the rate of 1 watt, the total energy used in 1 second is 1 joule. How much energy is used in one hour if it is used at the rate of 1000 watt?
It is (1000 watt) x (3600 seconds) i.e., 3600000 joules = 3.6x106 J. 3.6 x 106 J is defined as 1 kWh. The electric energy used in houses, factories etc. is measured in kilowatt hour. The cost of electric current is also fixed per one kilowatt hour. One kilowatt hour of electric energy is called one 'unit'.
