Power Energy
Electrical Energy
Electrical energy is power multiplied by the time over which it is delivered. With power in watts and time in seconds the result is in joules; with power in kilowatts and time in hours the result is in kilowatt-hours, the unit used on electricity bills. One kilowatt-hour equals 3.6 million joules. The formula assumes the power stays constant over the interval.
Electrical Energy
E = P × t
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| E | Energy | J or kWh |
| P | Power | W or kW |
| t | Time | s or h |
Conditions of application
Constant power over the time interval. For varying power, integrate power over time (or sum intervals) instead of multiplying a single value.
Worked example
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