Electric energy used or produced is the product of the electric power input or output and the time over which this input or output occurs:

Electric energy is what customers purchase from electric utility companies. These companies do not use the joule as an energy unit, but instead use the much larger and more convenient kilowatt hour (kWh) even though it is not an SI unit. The number of kilowatt hours consumed equals the product of the power absorbed in kilowatts and the time in hours over which it is absorbed:

kWh = Power × time

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