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Energy and kilowatt-hours

Power is how fast energy is used, and energy is power times time. The electricity bill is measured in kilowatt-hours. One kilowatt-hour is the energy a 1 kW appliance uses in one hour, which equals 3.6 megajoules.

E = P\cdot t

energy

1\ \text{kWh} = 3.6\cdot 10^6\ \text{J}

conversion

Symbols

$E$	energy	kWh
$P$	power	kW
$t$	time	h

Example

A 1.2 kW panel heater for 5 hours:

$E = 1.2\cdot 5 = 6$ kWh.

Power in kW times time in hours gives kWh directly.

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Part of Electric Power and Machines: The power system and energy.