Last edited 08 Mar 2019

Kilowatt hour

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A watt (W) is a unit of electrical power. One watt represents a current of one ampere with a voltage of one volt.

A kilowatt hour (kWh or kW h) is a unit of energy that is equivalent to 1,000 watts (1 kW) of energy being transmitted or used for one hour. The kilowatt hour is commonly used by utility companies for pricing, calculating and communicating electricity energy bills to consumers.

One kilowatt hour is equal to 3.6 megajoules – the amount of converted energy if work is done at an average rate of 1 kW per hour.

The difference between a kW and a kWh is that a kW is the energy required for an appliance to function, whereas a kWh is the amount of energy that is actually used over a period of time.

For example, a 100 W light bulb would take 10 hours to consume 1 kWh of energy. A 50 W electrical appliance that is used at a constant rate for 20 hours would use 1 kWh of energy. A 2 kW electrical appliance would use 1 kWh in 30 minutes.

To calculate the cost of running an electrical appliance, the power consumption in kWh is multiplied by the price per kWh. The unit price of electricity often varies depending on the rate of consumption, the time of day, and the location.

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