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Power station

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running costs

Using electricity

Energy is usually measured in joules, J. The joule is such a small unit of energy that if electricity was charged for in joules, the electricity meters and measurement systems would count very quickly and most household electricity bills would be for many millions of joules. Therefore, to measure electricity use without using lots of zeros, a unit of energy that is much bigger than a joule is needed – this is called the kilowatt-hour (kWh). One kilowatt-hour is equivalent to 3,600,000 joules.

A device that is rated as using one kilowatt (1kW) of power, such as an iron or a dishwasher, uses one kilowatt-hour of energy if it is on for one hour. Some devices use much more electricity than others e.g. tumble dryers, washing machines and kettles all use a lot of electricity, whereas lights, TVs, stereos and computers use much less in the same operating time.

Depending on the electricity supplier, how much electricity is used and the time of day the electricity is used, the cost of one kilowatt-hour can vary a lot.

Do you know how much a unit (one kilowatt-hour) costs from your electricity supplier?