kWh
Kilowatt-hour
A unit of energy equal to using one kilowatt of power for one hour. Electricity bills commonly price energy in kilowatt-hours: a 2 kW heater running for three hours uses 6 kWh, before allowing for controls cycling it off. A kilowatt is a rate of use, while a kilowatt-hour records an amount used.
Using kWh in context
Updated
A distinction worth remembering
A kilowatt-hour is an energy unit, not a power rating. A load's operating time and whether controls cycle it on and off affect its energy use.
Questions to take further
- How can I revise kWh beyond the definition?
- Explain what kWh describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Open University: relationships between electrical quantities — The relationship between voltage, current and resistance and the limits of an ohmic model.
Where kWh fits in the learning path
The Electrical Science section covers these units:
- Circuit Fundamentals
Curriculum mapping: C&G 2365 Units 202/302.
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- Ohm's LawElectrical Science
- Battery Energy Storage SystemsThe Regs and Practice Papers
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- Electrical Science — quiz previewFree · Electrical Science
- 18th Edition Exam — quiz previewPlus · The Regs and Practice Papers
3. Return to the meaning
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Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
Electrical energy is the amount transferred over time, measured in joules (J) or, on electricity bills, kilowatt-hours (kWh). A load drawing a steady 1 kW for two hours uses 2 kWh. Power describes the rate of transfer; energy describes the accumulated amount. A battery capacity quoted in kWh is therefore different from its power rating in kW.
Electrical energy
Read the Electrical energy entryCompare related terms
Open a meaning to compare its role with kWh, or follow its full entry.
Electrical energy
Electrical energy is the amount transferred over time, measured in joules (J) or, on electricity bills, kilowatt-hours (kWh). A load drawing a steady 1 kW for two hours uses 2 kWh. Power describes the rate of transfer; energy describes the accumulated amount. A battery capacity quoted in kWh is therefore different from its power rating in kW.
Read the Electrical energy entryElectrical power
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Read the Electrical power entryEfficiency
The share of input energy or power that becomes the intended useful output, usually written as a percentage. Losses such as heat mean a real transformer or motor delivers less useful power than it takes in. Efficiency compares input with output; it is different from power factor, which compares real and apparent power in an AC circuit.
Read the Efficiency entryA definition is a start. Using it in a real question is where it sticks.