Energy
An amount of electricity delivered or used over time.
The shaded area represents 6 kWh: a constant 2 kW over three hours.
Electrical energy is accumulated power over time. Electricity bills commonly measure it in kilowatt-hours, while grid-scale generation and storage often use megawatt-hours.
Adding up power over time
A kilowatt-hour is the energy transferred by a steady kilowatt over one hour. It is not a kilowatt divided by an hour. Electricity meters accumulate energy, which is why a bill normally includes a kWh total.
If demand varies, add up each interval’s power multiplied by its duration. A battery’s MWh rating describes stored energy; the separate MW rating describes its charging or discharging rate.
Why it matters
Energy units let us compare electricity delivered, consumed, or stored over a defined period.